Lawn Rehab (Practice)
Growing a Lawn
Most things necessary for lawn rehabilitation are also part of seasonal lawn care, except that if you’re rehabilitating a bad lawn you’ll probably need to do more of them more often for a while. A healthy lawn may need aerating only once every two to three years; a badly compacted one probably needs it twice for two years in a row, and at least once the following year.
Most of the heavy rehabilitation work gets done in spring or fall, while during the summer it’s important to keep up a good regime of regular maintenance. Remember that the primary focus of growing a healthy, organic lawn is to establish and encourage healthy grass, not to fight weeds or pests.
The tasks are listed here in the order in which they’d be done, in an ideal world. Since it’s not an ideal world, you’ll probably need to be selective. Say it’s fall and you’ve got an okay lawn without serious bare spots, weed patches, or thatch. Skip de-thatching and weeding, and instead aerate thoroughly (which will help control thatch anyway), and topdress with a mixture of compost and corn gluten meal. The compost, a soil amendment, will help improve soil structure, as does aerating, and the corn gluten will both fertilize the grass and kill new weed seeds.
Thatch is a layer of stems, roots and other dead organic matter that accumulates near the soil surface. A thick layer of thatch suggests overuse of synthetic pesticides or fertilizers, since these tend to kill off the micro-organisms that help organic matter to decompose.
Clippings often get blamed for thatch, and people rake clippings because they don’t want to contribute to thatch build-up, but this is a false problem with a non-solution. Clippings only contribute to thatch if they are excessively long, or if the thatch layer is so deep that it keeps clippings from decomposing.
It’s important to remember that thatch happens. It only becomes a real problem when the layer is thicker than a half inch, at which point it can become a breeding ground for insect pests and for various fungi. If you scroll through a page on fighting lawn insects or diseases, again and again you will see advice to remove excess thatch.
Removing thatch comes first on the lawn’s rehabilitation list because as long as it’s there it blocks water, fertilizers, and amendments from reaching the soil. It’s in the way of most of the other rehab practices one might undertake.
Dealing with Thatch
For everyday thatch of less than half an inch in depth, use a rake or a tool designed for removing the matted material. Top-dressing (adding a thin layer of soil or compost) can also be helpful, as the soil dressing contains microorganisms which will help the thatch to decay. For regular seasonal maintenance, these are all that should be necessary, and on many lawns they may only be necessary once a year or even less. Just check the level each spring and fall (see Thatch Control in Lawns and Turf).
For more serious thatch buildup, you may need to rent a vertical mower, a specialized machine that works vertically to break up and remove buildup.
Unfortunately, a vertical mower can be so hard on the rest of your lawn that you’ll often need to reseed after using one. Anything that hard on the lawn should only be used in spring or fall, when grass recovers more quickly than it can in the heat and stress of summer. Spring and fall are also the best times for overseeding, of course.
An alternative approach is to remove as much thatch as you can manually, then aerate like crazy and top-dress generously with compost. Aerating breaks up some of the thatch, while compost adds micro-organisms that help decompose what’s left. If you do this in spring and fall, you may well be able to bring even a thick layer of thatch under control without resorting to a vertical mower.
For information about specific weeds, go to the Weed Control section of Pets, Pests, and other Lawn Problems on this site.
Mow Long, Mow High
Weeds need light. They also need space. Thick, long grass forces dandelion and plantain leaves upwards, depriving them of both light and space. It also ensures that when you mow, you’ll be cutting their leaves as well as your grass. This won’t kill them, but it will help with managing lawn weeds. A longer lawn will also at least partially shade bindweed, and shade is one of the few things known to slow down that pernicious plant. Enough shade will almost entirely prevent bindweed from flowering and producing seeds. In a short-mown lawn, bindweed flourishes; in a long one, it has to make an effort.
Take Care of Your Grass
It may sound sickeningly simple, but it’s true: making your lawn healthy is not only the best way to ward off weeds, it’s the best way to beat back those you already have. That means having healthy soil with plenty of active microbes and earthworms, so topdress with compost, amend your soil as necessary, and overseed to encourage thick growth.
Skimping on lawn care and mowing closely give weeds the opportunity to move in, and as most of us know, getting rid of weeds is a lot harder than preventing them in the first place, because weeds tend to be hardy souls with huge root systems. I have it on excellent authority that Canadian Thistle, for example, can sprout from under a truck-load of gravel dumped on it.
Even while you’re trying to kill off weeds, therefore, take care of your grass. It may seem that you’re improving soil for the sake of the dandelions, but do it anyway: it’s the only way the grass will be able to compete.
Timing: When to Weed
There’s more on this topic under Seasonal Maintenance. While spring and fall weed control will put the biggest dent in the plant’s ability to recover and to reproduce, ANY TIME IS BETTER THAN NO TIME.
However, the seasonal secret to weed-control is this: hit them hard in spring and fall. In the spring, for instance, don’t let dandelions go to seed! Even if you’ve only got time to snap off the flowers, do that. (They’re edible, and make a lovely garnish in salad.)
The 50% Solution. If your assessment has shown you that your lawn contains more weeds than grass, it’s time to consider starting over. If that’s too expensive or too awful to contemplate, think about redoing the lawn one section at a time. If you can kill off the weeds in the back forty first, you’ll still have a lawn in front, however scrappy. Then, once you’ve got a lawn re-established in back, you can tackle the front portion.
The process requires killing off everything that’s there, then rebuilding a lawn from scratch. Even when a lawn is half-dead already, finishing it off can be difficult. The foliage can be killed with organic herbicides, but it’s hard to be sure that the roots and seeds are dead. This is why many people recommend black plastic, which deprives plants of both water and light, and which subjects them to high heat as well.
Tip: Scythe Herbicide is a non-selective, post-emergence weed control formulated to deliver maximum performance. Provides fast acting results on a long list of weeds and grasses, as well as most mosses and lichens. Very concentrated – 2.5 gallon concentrate covers up to 1 acre.
During summer, black plastic will kill most “ordinary” weeds in a few weeks. Deprived of light, plants cannot produce the foliage that feeds their roots, so they die. The black color also captures the sun’s heat, so that plants are solarized.
Yet some plants can withstand even this treatment. Nutsedge grows straight up through plastic, and must be kept down with a tough landscape cloth. The toughest cloth, though, wouldn’t even slow bamboo, which can grow straight up through concrete. Well-established bindweed grows so deep that even solarization will not affect its deepest roots. The taproots of mature creeping bellflower often start several inches underground, so they too are well protected from the heat of solarization, and like bindweed, they contain plenty of food to withstand a siege lasting a few weeks.
Both bindweed and bellflower can be killed, however, by depriving them of light for three years. For this long-term solution, weed-cloth on top of about 12-15 layers of newsprint works best, because while the plants are deprived of light, the soil underneath continues to receive air and water, so the soil remains active and alive.
Bamboo, which laughs at weed cloth, can be killed by repeated cutting or spraying of new shoots. This treatment is most effective when shoots are about two feet tall. As with any other plant, the food reserves stored in the roots will eventually be used up, and the root will simply be unable to send up any more shoots. At this point, the root itself begins to decay, and the plant dies.
If you’ve got dense patches of weeds in certain areas, use an organic herbicide on them or cover them over and let them die, and then reseed.
If your dense patches consist of weeds with major root systems (bindweed, kudzu, creeping bell-flower, poison ivy, Virginia creeper, nutsedge, even dandelions), then one spraying will not kill them, even if you use chemicals like Roundup®. The roots store enough food to send up new sprouts, sometimes numerous times, which is why we’ve all heard that we should get the WHOLE dandelion root, or the plant will grow back.
The only way to kill these plants is to deprive them of foliage for three years (sometimes more, in the case of kudzu) so that the roots are finally depleted and can’t send up new shoots. Anything that keeps the plants from producing foliage will work: persistent hand-weeding, repeated herbicide spraying, covering over, or digging out. The choice depends on what works for you. If it’s a thick patch, or big, it’s usually easier to dig it out or cover it over than to try to weed or spray it as often as is necessary.
Even Kudzu (Pueraria lobata), a voracious vine that appears to swallow trees whole, will respond to these tactics, though its growth patterns and sheer size are so unusual that tackling it requires different techniques and equipment. (Apparently a skip loader can come in handy.) There’s a short section on kudzu control here.
Weeding or Spraying. These are most effective in spring, when the plant puts a lot of energy into new foliage. It’s fine to wait till the sprouts are big enough to grab easily; at this stage, the plant has a fair amount of energy invested in the shoots, so when you pull them, you give it a significant set-back. It may not be necessary to weed or spray as often in summer, but don’t let shoots get too big, because that greenery is what feeds the roots, and it’s the roots you must kill to kill the plant. Try to make sure that you spray or pull the last foliage in fall before the cold would kill it off, so that the roots can’t be renewed before winter. This means they’ll start the spring at least somewhat diminished.
Digging Out. With perennial weeds that have extensive root systems, this is an effective if time-consuming (not to mention exhausting) control. Be prepared for a mess, for a major investment of energy, and for careful follow-up. The advantage is that, aside from the monitoring, the whole thing can be done in a couple of days.
This may be the best way to tackle a bad patch of dandelions, it works well for bellflower, and it will work for new bindweed. Well-established bindweed has roots too deep to dig.
The only essential equipment (besides strong legs) is a spade, but a tarp gives you a place to pile the dirt without making a mess of your grass. In case you can’t finish the job within a day or so, a tarp can be dragged to another spot (assuming it’s not too heavy), so no one patch of grass gets deprived of sun for more than a day or so.
The process is simple: dig out the dirt, sift it for roots, and return it to the hole. Sifting through a screen laid over a saw-horse or wheelbarrow can make the process easier. The catch is that no one can dig out every scrap of bellflower root or dandelion; the bits that are left will start new plants. This is why it’s essential to monitor the area closely for a year or two afterwards. If all goes well, the only plants you’ll see will be tiny, new ones, easy to dig out. Even if it turns out that you missed a major tuber, digging it out should be easy, as the dirt has been loosened recently.
If the patch included some good grass, try to preserve it as sod, but be sure it doesn’t contain any weed roots!
When you’re done, you’ll need to seed or patch with sod. If you saved some weed-free sod, place it here and there on the surface of the patch, so that it can gradually spread to fill the whole area.
Cover Over. The idea here is to cover the entire patch, depriving the weeds of light for long enough (three years) to kill even major roots. The two materials used most often are black plastic mulch or a weed cloth, but a thick layer of newspaper (12-15 sheets), either on its own or in combination with the weed fabric, is another option.
Plastic has the advantage of heating up the soil underneath, so it works well for short term summer solarizing. However, it prevents air and water from reaching the soil, so if you’re laying down a barrier that will stay in place for several years, weed cloth or newspaper is preferable. As long as you create a complete light barrier, the weeds will die, but if you allow for the passage of water and air, the soil will not.
Weed cloth alone often does not keep out all light, so another layer of something — newspaper underneath, or bark or pebbles on top — is a must. Good weed-cloth is also tough enough to withstand foot traffic and to keep down nut sedges, which will grow straight up through most plastic mulches. On the other hand, in a sunny area where no one walks, black plastic alone will solarize the soil, literally cooking plants as well as depriving them of light and air. Newspaper can create a biodegradable light barrier for use in no- to low-traffic areas, but it is more work to install.
Tip: Weed-Shield Weed Barrier blocks out weeds while allowing water, air and nutrients to pass through to the soil. Easy to use, just place on the soil and cover with a mulch. Professional grade — lasts 20 years!
Whatever you choose for a weed cover, lay the edges flat on top of each other (keep dirt off!) and overlap them at least six inches so that roots can’t just sneak between them. Be sure also that your cover material extends out well beyond the edges of the patch, or the weeds will emerge around the outside of the former patch, giving you a new, larger, donut-shaped weed patch. If extending beyond the weeds makes the covered area unacceptably large, dig out the weeds around the outside of the patch before laying down the weed barrier.
Landscaping. Unless swathes of black plastic in your garden pleases your eye, you’ll probably want to cover them in some way. The simplest option is lay down wood chips, pebbles, or bark, but it’s also possible to plant in the midst of the covered weed patch, or to establish a small garden on top of it.
If your weed patch is under evergreens in an obscure corner of your garden, you have built-in landscaping: pine-needles. Rake away a heavy layer before putting down the newspapers or weed cloth, then rake the needles back without disturbing the weed cover.
For a weed patch in the middle of the lawn, you may want a different look. You could just cover the patch and dump the mulch of your choice on top, but there’s an excellent chance that your chosen mulch will gradually slide off this little mound into the surrounding grass, clogging lawnmowers and — horrors — exposing the weed cover. To avoid this frustration, dig out a couple of inches of dirt or sod over the weed patch before covering it, trying to leave a level surface so the top mulch doesn’t all retreat from the edges or collect at one side. Since the dirt you dug out is probably infested with nasty weeds, be careful where you put it.
Neatly edged borders and a mulch can do much to redeem a weed patch. Bedding plants around its edge and a couple of bushes or perennial flowers in its midst can complete its transformation into an attractive feature, even if it’s smack-dab in the middle of your lawn.
Planting in the middle of a weed patch is chancy; no matter how careful you are, a few weeds will probably emerge near the stem of the plant. Therefore, use the bare minimum number of plants necessary to make the patch look like a garden instead of an eyesore or a curiosity. Since you’ll certainly need to weed near the stems and you won’t be able to use a hoe without disturbing the weed-cloth, choose plants that are neither too prickly nor too low-growing. Crawling under a rose-bush to weed near its stem is not what most consider a pleasant chore.
Finally, only perennials should be planted through weed-cloth, since once the plants are placed, the weed-cloth and soil should not be disturbed for several years.
To prepare for plants, prepare a planting hole before you lay down whatever cover you’re using. Dig out the worst of the weeds around the hole so that you’ve slowed them down if not finished them off. Pile the dirt from the hole in a bucket and keep it handy. When you lay down the weed cloth, it should be easy to locate the places for the plants, since there’s no dirt there. Cut an X in the cloth, making a hole big enough to admit the plant’s root ball, but no bigger. Lower the plant’s roots into the hole through the X, then use a trowel to pour the dirt from the bucket into the hole. Tamp it firm, water it well, then close the X around the plant’s stem, using garden staples to secure the weed cloth closely around the plant. If you want to be doubly careful, lay another, uncut circle of weed-cloth over the first to cover the gaps where the X was cut.
This is not a completely weed-proof system, but it’s close. It leaves so few cracks through which weeds can emerge, that it’s easy to keep them in check with manual weeding. After three years, they should stop showing up entirely, because their roots, consistently deprived of foliage, will die.
Bedding plants should not be planted through weed cloth. This would involve cutting too many holes in the cloth, through each of which weeds can emerge. Instead, finish covering the patch with plastic, newspaper, or weed cloth, and then dig out a foot-wide ring around it in which to place the bedding plants. To protect that ring from invasion by grass, you can edge it with a hard plastic weed barrier, available at most hardware stores. After you’ve amended the soil in the ring with compost and fertilizers, (probably a good idea, since it’s been part of a lawn for years) you can place the bedding plants.
Last, spread your top mulch — pebbles, bark, or wood chips — over the patch, around the perennial plantings (if any), and around the bedding plants. The weed cloth will disappear, and the bedding plants will now edge a continuous, attractively mulched landscape feature.
A weed patch under a tree or on a slope presents a different challenge with different solutions. The pebbles-on-weed-cloth arrangement described above won’t work on a slope because no matter what you do, the top mulch is going to slide around. It may not work well under some trees, either, where roots make a level surface an unobtainable ideal, and just getting weed-cloth to stay down so that it actually suppresses the weeds can be a considerable challenge. Digging weeds such as creeping bellflower out of a lawn is an option, but it can be nearly impossible under a tree.
In situations like these, you might want to think about establishing a garden on top of weed cloth, and what often works best is a rock garden (see Rock Gardens: Alternatives to Turf). If you just lay weed cloth over the ground and pile dirt on top of it, you’ll have an odd-looking hill that will leak dirt with every rain. The rocks help to stabilize the dirt until plantings can take hold, and they can give a dirt-pile the look of intentionality, as if it’s actually serving a purpose in the world.
Begin by digging into the soil for six inches to a foot, (depending on roots, slope, and energy), removing the biggest and worst of the offending weed roots. This will set them back and make it unlikely that they’ll rally enough to sneak round the edges of the weed cloth. Lay down weed cloth or newspaper (12-15 pages thick) — NOT PLASTIC — and if possible secure it with stones or garden staples. Weed fabric is called for because this will be a permanent installation, and cloth will allow microbes, water, and air to travel freely between the different soil levels. Plastic, on the other hand, seals off the upper layer of soil from the lower one, preventing the interchanges that keep soil healthy. Furthermore, in a heavy rain, plastic could act like a bowl, drowning your plants.
Once the weed cloth is in place, pile soil on top. If you’ve managed to get the original top-soil weed free, use that, adding amendments as necessary, and more soil until you have a shape and height that pleases you. Place rocks artfully, and plant shallow-rooted perennials amongst them. Annuals are not a good idea because the less digging and replacing you need to do in early years, the less likely you’ll puncture the weed cloth and release the weeds beneath it.
As long as the lawn has less than 50% weeds, weeding, spot-spraying, and cultivating the grass are still options. The key is to finding a system, and a tool, that you can stick to.
Organic Sprays. One good easily available spot-removal for weeds is vinegar. (It works great against the aforementioned Canadian thistle as well as spotted knapweed, another bane in the West where I live.) Just keep in mind that this is truly spot removal. Spray it only on the weed. The vinegar will kill the foliage of any plant that it meets up with, and in the case of many garden plants (though too few weeds, alas!) that means it will kill the plant. To ensure that it touches only the weed, you can spread newspaper around it, so that any stray droplets will fall on the paper, not the lawn.
Tip: Bradfield Horticultural Vinegar is an inexpensive and environmentally safe weed killer. Contains 20% acetic acid (household vinegars contain 5%) and includes yucca extract — a natural surfactant and penetrating agent — to completely cover weeds and undesirable vegetation. Works fast (within a few hours) and degrades quickly in the environment.
Other organic herbicides available at good gardening stores are usually based on clove oil or on lemon. The principle in all cases is the same, to cause the plant to dehydrate and die. They work well, but they are not carried into the root system, so repeated sprayings may be necessary. (This is true also with conventional herbicides, as you may have noticed. A real problem isn’t solved by a single treatment.)
New and Improved Dandelion Weeders. The old-fashioned dandelion fork certainly has its place and may be all you want or need. If you find it hard on your back or your knees, however, the Yard Butler Rocket Weeder may revolutionize your life — at least, the weeding part of it. The popper is a light-weight metal tool, about two and a half feet long, with a claw at one end and a handle and release at the other. You set it over the offending plant and press it into the ground with your foot. This drives the claw prongs downwards and together, so that when you pull the thing back up again, it bring with it both the dandelion and about two inches of root. Not bad. When you squeeze the release at the handle, the weed with its plug of dirt drops out. Just think — you aerate as you weed.
A second tool requires some bending but little effort. The Dandelion Terminator is a special blade designed to fit into any standard electric or cordless hand drill. Made of steel and a good inch wide, it will pulverize your dandelion roots to a depth of four inches or so. Just walk around your yard and drill those dandelions away. (Unfortunately, the Dandelion Terminator is no longer commercially available.)
The Spade. Take a spade to my lawn? You must be joking! Well, no, but I do recommend one with a small, round-tipped blade. With this implement, you can tackle major dandelions, bell-flower, or bind-weed in the lawn. For individual plants (single offenders), set the blade one to three inches from the base of the plant (distance depends on plant size, soil density and other things — you’ll develop a feel for this if you use this technique often), press it all the way into the earth, and push down the handle. This should raise a cleanly cut semi-circle of earth, with the weed at the center. If there’s plenty of foliage on top, it’s often possible to pull the weed cleanly from the soil. Sometimes, it’s easier to grasp the root itself, and pull it down out of the sod. When you’ve got it free, lower the soil back down and press it into place with your foot.
All signs of this surgical extraction generally disappear within a week, if not sooner, but if the process is too messy for you, save it for fall. When the summer season ends, a few cuts in the sod will probably not seem much of an aesthetic problem. These cuts, incidentally, aerate the soil, as does removing large roots. The rush of spring growth should completely repair any damage done.
If you’re tackling a small patch of weeds (multiple offenders) it sometimes makes most sense to remove the sod first, laying it in the shade on a plastic bag or tarp, so you can really dig into the soil below and get multiple roots without wrecking your lawn. Before you return the sod to its place, turn it upside down, and get all the weed roots, or you’ll just be replanting weeds. It’s okay to loosen and even remove soil from around the grass roots as you do this. Yes, it puts some stress on the grass, but leaving major weeds in place will stress it more. Once the sod and loosened dirt is weed-free, return first the dirt, then the sod to the ground. Keep the area well-watered for a couple of weeks while the roots re-establish themselves.
NOTE: The ground should be damp when you undertake this. Removing sod when the top-soil is dry lets the grass-roots dry out very quickly, and the grass can die. If you get interrupted before you have a chance to return the grass to the ground, you can do several things to keep it alive:
• Make sure it’s in the shade.
• Cover it at night with a sheet, row-cover, or part of the tarp.
• By day, keep it covered with a row-cover or old light-colored sheet — something that lets light through.
• Water it if necessary.
Staying Comfortable: Hat, Mat, Music, Basket — and Shade. Don’t underestimate the importance of comfort. I’m convinced that one of the major reasons people generally hate weeding is that they’re physically uncomfortable while they’re doing it.
So, what makes weeding uncomfortable for you? The hot sun? Bending over? Getting up and down? Boredom? Pinpointing the problem may help solve it.
Having the right tools can make a profound difference. Try to make them easy to get at, especially if you often weed spontaneously for short periods of time. Perhaps put everything into one basket, so you don’t have to hunt around for them. If you don’t have a basket and don’t have time to think about getting one — life can be that busy — use a cardboard box. It won’t be pretty, but it’ll do the job. Or keep your favorite tools — weeder, kneeling pad, and gloves — by the back door, where you can easily snag them on your way out.
Tip: The Yard Butler Garden Kneeler converts from a portable 17-1/2″ tall bench for sitting to a cushioned kneeling pad by simply flipping it over. Folds flat for easy storage.
The three things listed above are only some of the options that make weeding less painful. The padded bench saves your knees, the hat saves your eyes and skin, and the music can make all the difference. Trading weeding days with a friend can mean that the job becomes almost a pleasure, instead of a dreaded chore. Gloves are essential to some, hated by others. If you need sunscreen, which is easier: to put it on first thing in the morning, or to keep it with your gardening basket?
Aerating may be the single best, long-term thing you can do for your lawn, but you should only do it if the season is just beginning or almost over. Aerating your lawn involves using a special tool to dig little plugs of dirt out of your lawn so that air and water can reach roots. (Yes, it does look like hundreds of tiny turds all over the grass.) Do this in early spring or in fall, and the grass will be stimulated. Do it in mid-summer when the grass is in a quiet, retiring mode, and you can damage rather than improve it, because you are cutting roots which the plants need to get water and nutrients.
A number of things can cause or contribute to compaction. Obviously, first among these is heavy use, which is why paths are almost always compacted. But a thin layer of topsoil, for instance, will compact more quickly and completely than a thick one, and clay soils, being composed of such minute mineral pieces, compacts more quickly than do sandy soils or soils containing plenty of organic material. Lawns that have not been recently aerated are likely to be compacted, as are those in recently built subdivisions where building and landscaping were done by machine. Finally, and this one may come as a surprise, walking on the lawn when it is frozen or snowy will lead to compaction.
As is clear from this summary, aerating is only one of several things you can do about a compacted lawn. Topdressing the soil (adding material on top, rather than digging it in) helps as well, especially if the topsoil is thin or heavy with clay. An inch of organic compost or high-quality soil, perhaps mixed with peat moss or coir (coconut fiber) will absorb and hold water and will encourage earthworms, whose tunnels allow water and air to circulate.
Building paths where paths seem to appear can also help relieve compaction, or at least eliminate muddy paths. Pebbles, added in new layers as old ones work down into the soil, will eventually form a solid, well-drained pathway where puddles won’t collect. Paving stones, even it they have spaces between them, take some of the wear off the grass and spread the impact of the foot stepping on them over the whole surface of the stone. Bricks perform similarly. Those designed with holes in them can entirely disappear into the lawn, if the grass is allowed to grow through those holes and between bricks.
Soil that’s badly compacted needs to be aerated twice a year, spring and fall, for several years. After that, if you’ve also been amending it as needed and adding organic matter, it will probably only need aerating every three to five years, depending on your soil type and on how much use the yard gets.
Where fertilizers supply nutrients, amendments adjust soil pH and improve soil texture. The simplest problems (to understand, if not to solve) involve soil with too fine or too coarse a texture, or with poor structure. These soils will present drainage problems, either holding onto water too long and thus depriving plant roots of oxygen, or letting it drain away too quickly, before plants can make use of it.
Less obviously, problems with either pH or with texture and structure can create the seemingly paradoxical situation in which a soil contains plenty of nutrients, but the grass growing in it cannot make use of them. This can happen for a number of reasons. Soil that drains too quickly, for instance, doesn’t merely deprive plants of water; it also deprives them of the nutrients that would dissolve in that water and move into the plant roots via osmosis. A pH imbalance in either direction can slow or prevent the chemical exchanges necessary to free up certain nutrients or to permit them to move into the roots. Soil that’s either too acidic or too alkaline will not support plant life at all.
Appropriate soil amendments can address most of these problems.
To Improve Soil Texture and Structure
Compost. Compost is the only universal, the one thing it’s never a mistake to add. It won’t solve every single problem, but it alleviates most. It improves drainage in both sandy and clayey soils, helping the former hold water and the latter release it. It encourages earthworms, which help aerate soil and provide the richest of nutrients. It helps balance pH, relieving both overly-acidic and overly-alkaline conditions. It helps prevent thatch build-up by adding and encouraging the micro-organisms that break down organic materials.
Peat and Sphagnum Moss, Coconut Fiber. Like compost, all of these products add organic bulk to soil, thus improving drainage in both sandy and clayey soils. Unlike compost, they contain very few nutrients, and unlike compost, which tends to balance pH, these amendments are all somewhat acidic, the mosses more so.
All of them absorb up to twenty times their weight in water, which makes them ideal for sandy soils. Since water retention is already a problem in clay soils, it seems counter-intuitive to use them there, but they also help break up and separate clay particles, relieving the compaction that causes clays to drain so poorly. Furthermore, they absorb water quite readily, which clays do not, so these products do in fact help the drainage problems endemic to heavy, compacted, and clay soils.
Mature Manures. The key word here is mature, meaning well-rotted, since raw, or fresh, manures differ from their grown-up relatives significantly in terms of what nutrients they contain and what chemicals they emit. Where the manure comes from — what animals emitted it — also makes a difference; chicken and other fowl manures are “hot,” or rich in nutrients, and must be composted before use or they may “burn” your lawn or other plants (see Land Application of Animal Manure). Steer manure is even different from cow manure, being higher in salts and often in weed seeds.
Pay attention to where your manure comes from. What the animal eats, it excretes. If it eats grass or grain treated with pesticides, some may end up in your soil. This is of less immediate concern with lawns than with vegetable gardens (you probably don’t eat your grass) but it is still something to be aware of. Some countries still use insecticides containing organo-chlorines, a highly toxic group of chemicals that includes dioxins, the most toxic substances known. (DDT is a dioxin.)
Large-scale manure production, use, and storage, especially the lagoons that hold both liquid and solid animal waste at some hog and dairy farms, can cause serious environmental problems. These include pollution from burst lagoons, health problems from exposure to the ammonia that manure produces, and eutrophication in waterways when the nitrogen in manure overstimulates water-plants, which deprive fish and other organisms of oxygen.
Most of these problems do not directly affect the application of manure to a lawn, as long as you use it responsibly. The ammonia that will volatilize from the manure you spread on your yard is probably not great enough or concentrated enough to do anyone any harm. Avoid letting manure wash into waterways, however. Try to keep all of it on the grass (not the path or the driveway), and don’t apply it when or where it could wash directly into storm drains or streams.
NOT RECOMMENDED: Sawdust and Other Wood Products. All decomposition requires nitrogen, but since sawdust is itself very low in nitrogen, it requires far more than, say, leaves or grass clippings. This means that while it is decaying, it ties up soil nitrogen which is therefore not available to plants. Once it has decayed, the nitrogen is released and once again becomes available, but in the meantime wood products can cause nitrogen deficiencies. This is not what you want from your soil amendment. If your heart is set on sprinkling sawdust on your lawn, add nitrogen (organic cottonseed meal, blood meal) at the same time to offset the possibility of nitrogen deficiency.
Composted sawdust is a whole different story. But again because it is so low in nitrogen, it and other wood products compost quite slowly, unless you add a good deal of green organic matter or some other source of nitrogen such as blood meal to the mix.
Before using sawdust, wood shavings, or other wood products, whether on the lawn, in compost, or as a mulch, be sure that they are not contaminated with any paints, stains, preservatives, or other products, as some of these can contain heavy metals and other toxins.
To Raise pH (make soil more alkaline)
Lime. The standard amendment to raise pH is lime, which you can buy as granules or pellets, or as any of several powders. IT IS IMPORTANT TO KNOW WHAT KIND OF LIME YOU ARE BUYING, because different forms have different properties, and some are dangerous to handle. While some will work just fine on established lawns, others are more likely to damage your grass than improve it. Finally, just to keep you on your toes, most limes have one or more common names, which makes knowing which you’ve got both more difficult and more important.
Limes are basically calcium, one of the three secondary nutrients (after nitrogen, phosphorus and potassium) required by all plants. All lime is mined and crushed, but some forms undergo additional processing as well.
The simplest forms are calcitic lime (calcium carbonate, a.k.a. agricultural lime or aglime), dolomitic lime (calcium magnesium carbonate CaMg(CO3)2), and marl.
Calcitic lime supplies only calcium, while dolomitic lime supplies magnesium, another secondary nutrient, as well. Since magnesium is less available to plants at higher pH levels, its presence in dolomitic lime can protect plants from potential deficiencies in soils low in magnesium.
Marl, a.k.a. bog lime (a calcium carbonate) which is mined from rocks originally formed under lakes or oceans, usually contains high quantities of clay (as much as 35%) and can contain other impurities as well, so it is not generally a good choice for agricultural purposes.
All three of these limes come from rocks that are mined and crushed to a fine powder that can be applied directly to your lawn. Since limes are relatively insoluble, they won’t dissolve and spread out to reach roots where haven’t been applied. It’s important, therefore, to spread lime evenly. The white powders show up nicely on grass, letting you see where they’ve fallen and where not, but they are so fine they can sometimes clog spreaders. If you have this problem, you can try granular or pelletized lime which is made by combining an inert glue-like resin with one of the powdered forms to make a product that is easier to handle than the fine powders.
Burnt (or unslaked) lime and hydrated (slaked, or quick) lime are the more concentrated, more highly refined, and potentially more dangerous forms. BE CAREFUL while handling either hydrated lime or burnt lime, as both are highly concentrated caustic alkaloids that can react violently with water or with acids. They can also burn your grass, so they are not recommended for established lawns but only for amending soil before putting in a new lawn.
If you do use hydrated lime, here is the formula:
- for sandy soils, add 4 ounces per square yard;
- for loamy soils, add 8 ounces per square yard;
- for clay soils, add 12 ounces per square yard;
- for peaty soils, add 25 ounces per square yard.
Lime doesn’t dissolve easily, which has both advantages and disadvantages for gardeners. (Technically, it is immobile.) The disadvantage is that only the lime closest to a plant’s roots is available to it. A nutrient that dissolves easily, like nitrogen, will move through the soil with water, and can reach a plant from some distance away. Not lime.
In practice, this means that it must be spread evenly and thinly. If you miss a small patch of grass when you are spreading, the lime nearby will not dissolve with the next rainfall or watering and travel into adjacent soil. It stays where it is put. (Think of the chalk (a closely related substance) which is used on sports fields: the stuff does not scatter nearly as much as you might expect.) Given this property, it needs to be in direct contact with soil to be effective. It does, however, need water to take effect, so water after applying it. This will also wash it down through thatch to the soil, and will keep it from blowing away.
The advantage to lime’s relative insolubility is this: because it doesn’t dissolve readily, it won’t leach out of the soil quickly. This means that it’s usually necessary to apply lime only every three years.
Unfortunately, this can cause its own problems. If you’ve applied too much, you may not see the results until two or even three years later, and by then you may not connect your yellowed, slow-growing grass to the lime you applied years earlier. So follow the directions. It’s worth making the effort to apply the right amount and to apply it carefully.
Wood Ashes. Because they are rich in micronutrients and because they are easily soluble, ashes are particularly suitable for use on lawns, where it is impractical to dig in amendments and where the long-term growth of a single crop (grass) with a shallow root-structure can exhaust the soil of certain key nutrients. The draw-back is their high potassium content, which dandelions crave and most grasses don’t. Kentucky bluegrass, however, requires about the same amount of potassium as dandelions, so ashes remain an excellent option for these lawns.
Not only will ashes raise the pH of the soil, but they also contain a number of necessary plant nutrients, including boron and other trace elements. Beyond these, they are 15 to 50 percent calcium, a secondary nutrient, and they supply two of the big three primary nutrients, potassium and phosphate. They don’t contain nitrogen, the primary nutrient most needed by grass and other green plants, but this is easily supplied through other products.
Occasionally, usually in a gardening blog or a forum, you may see a warning that wood ashes contain heavy metals, which can be highly toxic. They do — but in trace amounts. A number of recent, long-term studies, (Finnish, Latvian, and American) some of forests in burned-over areas, some of crops where ashes were added as an amendment, have looked at whether crops and trees take up heavy metals from wood ash. None of these studies has found an increase in metals in the berries or mushrooms or pines grown on soil treated with wood ash, and no government or institute or university I know of has warned against using wood ashes. In fact, at least two universities — Georgia and Wisconsin — have released reports supporting the use of ashes as an amendment.
The exact composition of wood ash varies considerably, depending on factors like what kind of tree it comes from and how completely it burnt. Ashes from hardwoods will contain more calcium than those from softwoods, and as noted above, the total calcium content can vary hugely. This is one reason why ashes need to be applied in small amounts: there’s no easy way to know precisely what you’re adding.
Since ashes are so soluble, they can make soil quite alkaline when first applied, so it is best to spread them several weeks before seeding. Once plants are established, ashes can be used as a mulch or a side-dressing. On the soil surface, they may repel slugs and snails.
Ashes are so fine they can be difficult to apply. The problem is magnified when spreading them on a lawn, since they will not be dug into the soil but will just sit on the surface. Wait for a windless hour, and either scatter the ashes with a scoop held only a foot or so above the ground, or pre-mix them with something heavier such as sand, soil, or compost, and use a spreader.
Coconut fiber and peat moss, themselves airy and liable to blow away, seem weighty compared to ashes, so they can also be used to weight and distribute wood ash. Both, however, are acidic, so they will slow the liming effect of ash. Coconut fiber makes the better choice if you are trying to make your soil more alkaline, as it has a slightly higher pH.
Water immediately after applying, to bring the treatment into contact with the soil and to prevent its being blown away by the next breeze. Water is also necessary for the chemical process that creates the alkalinity.
Note: Take care not to breath ashes; they become caustic when wet, and mucus membranes are wet. As long as you don’t breathe them, handling dry ashes does not cause any health problems for most people, but damp ashes can irritate or burn the skin. For these reasons, some sources advise wearing gloves and a mask when handling wood ashes.
To Lower pH (make soil more acid)
Various organic materials such as peat moss, cottonseed meal, and leaf mold, as well as the inorganic (but natural) product elemental sulfur, will all make soils more acidic. Which one you use will depend on the particular properties of your soil together with those of the various amendments, as well as what’s available and what you can afford.
Elemental Sulfur. This is the classic amendment for lowering soil pH, widely used in agriculture, lawn care, and gardening. It does take time to act, so don’t expect instantaneous results. This is also an amendment that needs to be mixed into soil, not just sprinkled on top of it, a somewhat problematic fact if you’re dealing with an established lawn. One way around it is to mix the sulfur with compost or topsoil and spread it as a topdressing.
• On sandy soils, add 1.2 oz of ground rock sulfur per square yard.
• On all other soils, add 3.6 oz per square yard.
Peat Moss. This will lower pH while adding organic matter, but its pH punch is weak compared with that of sulfur. The best peat moss, sphagnum, adds significant organic matter to poor soils, so if your pH problem is minor, this can be a good option.
Leaf mold. Leaf mold also will lower pH somewhat while adding organic matter. Well-decayed leaf mold is a compost, so it will also improve soil structure as well (see Using Autumn’s Bounty). Only well-decayed or thoroughly chopped leaves should be spread on lawns, as otherwise they will block the sun, killing the grass beneath them.
Cottonseed Meal. This is another product that will lower pH, though its primary use is as a nitrogen-rich fertilizer (6-1-1). Since it has only a low-level effect on pH, it should not be used unless adding nitrogen is also called for and the pH imbalance is minor.
Check that any cottonseed meal you buy is organic, as it may otherwise contain significant residue from insecticides that were sprayed on the parent cotton plant.
To Improve Water Retention in Sandy Soils
Compost. As always, compost is the first line of defense, since unlike sand it holds water well. The real surprise may be that you don’t have to stir it into the soil (though doing so gives it a jump-start, of course); worms and micro-organisms nourished by it will carry it downwards, incorporating it gradually and improving the sandy soil’s ability to retain water in the process.
Coconut Fiber (coir) or Peat Moss. Both of these products are extraordinary sponges, and they will retain this quality when added to your soil. They can be mixed into soil before seeding a new lawn or used as a top-dressing over an existing one. Be sure to water immediately after applying either of these, or they will drift away on the next breeze.
Coconut coir is the preferred choice for environmental reasons: it comes from coconut shells, while peat moss grows over thousands of years in bogs with fragile eco-systems.
To Improve Water Drainage in Clay Soils
Compost. Again, compost. Compost not only breaks up clay soils, allowing for the easier movement of water, oxygen, and nutrients, but it also provides food for worms — and worms, in turn, aerate soil as they travel through it.
Coconut Fiber, or Peat Moss. These products lack the nutrients and microorganisms present in compost, but they nevertheless add organic matter and improve heavy soils significantly. Like compost, they are effective on both clayey and sandy soils, for they hold many times their weight in water, (just what the doctor ordered for sandy soils) while in heavy, clayey soils they help break up the solid clay clods, introducing oxygen, allowing for better drainage, and thus easing both the growth and the work of roots.
Sand. There’s quite a difference of opinion about the advisability of adding sand as an amendment to improve clay soils. It seems a straightforward solution to the problem of heavy soils that have an over-abundance of very fine mineral particles and a paucity of larger particles: add the bigger particles. A number of sources, however, warn against it, emphatically. Mary Ann Rose, Commercial Landscape & Nursery Specialist at Ohio State University (no link available at this time), says that the result is usually “a disaster, while the Extension Service at Colorado State University says simply, “Don’t add sand to clay soil — this creates a soil structure similar to concrete.”
Other sources, though, do recommend sand. The Denver Water site, for instance, says that “clay soils… often require sand as well as organic matter for full amendment.”
As this quotation suggests, the cement problem appears to occur when sand is used by itself. Two guidelines emerge: first, don’t depend on sand alone as an amendment in clay soil. Use plenty of compost and other organic matter as well. Second, sources that do recommend sand warn against river sand, whose rounded particles, worn by erosion, allow clay particles to pack closely around it. Builder’s sand, however, or “sharp” sand, has more angular particles, which create a more porous soil with a better soil structure than that you’re likely to get with river sand.
The Special Case of Gypsum
Gypsum has several undisputed uses as an amendment, yet its value, like that of sand, is frequently debated or dismissed, and on-line discussion of its utility is both confusing and confused. This is in part because gypsum gets recommended for a wide variety of soil problems (including both raising and lowering pH) but its effectiveness for each is limited by very specific chemical conditions. It works in some cases, but not in others. Another source of confusion results from the fact that so many pages on it are written by university extension offices which are addressing the conditions of a particular state or region. It is difficult to find an overall discussion that’s accessible to the lay person. One of the best overviews I’ve encountered comes from the University of Minnesota, and is titled The Value of Gypsum. Though this page does address the applicability of gypsum in Minnesota, its authors also have the grace to list the various uses for which gypsum is recommended and to explain, in plain English no less, the action of each.
Agricultural Gypsum is an excellent source of both calcium and sodium sulfate, it reduces or neutralizes aluminum in some soils (mostly in the South-West), and it can, in some cases, loosen or “flocculate” heavy, clayey soils. In addition, it helps restore some sodic, or alkali soils – this is the “lowering pH” part of the legend – and some forms of gypsum can act as liming agents – here’s the “raising pH” part.
At least some of the controversy and confusion arises because there are several types of gypsum (as there are lime), and the exact mineral composition of natural (mined) gypsum varies. Absolutely chemically pure calcitic gypsum (hydrated calcium sulfate (CaSO4•2H2O)) does not raise soil pH. However, a lot of mined gypsum contains dolomite, which does raise soil pH and which supplies magnesium, an important secondary nutrient, as well. This difference mirrors the distinction between calcitic and dolomitic limes, save that both limes will raise pH, while only the gypsum with dolomite will. Some gypsum may contain lime in one of its several forms, and that lime will raise pH.
Since pure gypsum is pH neutral and lime is not, gypsum is a better source of calcium for soils which lack that mineral but which have a balanced pH, as the University of Minnesota site mentioned above points out. However, if you are trying to raise your pH, pure gypsum is a non-starter.
By far the most common lawn and garden use for gypsum is to “loosen” or “lighten” clay soils, and it is here that the controversy rages. Gardening stores across the country sell gypsum, and homeowners and gardeners across the country trustingly purchase it to increase the porosity and improve drainage in their clay soils. Unfortunately, gypsum only works on some clays. The widespread but misguided use of gypsum may explain the terse tone of some sites, which declare categorically the uselessness of the stuff.
Why gypsum works to loosen some clays and not others involves some fairly complex chemistry that touches on clays, pH, soil structure, electrical charges, Van der Waals forces, sodicity (as measured by sodium adsorption ratio (SAR)), salinity (as measured by electrical conductivity (EC)) and probably other stuff I’ve never heard of.
Clay is a problem because it tends not to form the small clumps, or aggregates, that make soil porous, allowing air and water and roots to penetrate them easily. (You may think your clay soil has plenty of clumps, but technically speaking those are clods, much larger and harder than the aggregates considered desirable.) Good soil structure depends on aggregation and on the materials that promote it, called flocculants.
The short story on gypsum is that it flocculates only sodic soils that are not saline, in other words soils high in sodium and low in other salts such as magnesium and calcium. Sodium causes clays to disperse, while these other minerals actually help it aggregate. Gypsum’s high calcium content means that it can flocculate soils that are high in sodium.
Since gypsum can help restore sodic soils, which usually have a high pH, it has gained a more general and undeserved reputation for lowering pH. What actually happens is that the calcium in the gypsum replaces the sodium ions, which can then be washed or leached from the soil. On an agricultural scale, however, this requires hundreds of pounds of gypsum for an acre of land, and then a whole lot of rain or flooding with irrigation water that isn’t high in sodium.
How Gypsum Works: The Chemistry of Clay
This explanation leaves out a lot, but it does cover key aspects of the relevant chemistry.
Clay particles are very small and flat, so they usually lie in closely packed parallel layers that impede the free movement of air and water and the growth of roots. Since clay soils compact easily, it might seem that aggregates, in which the particles are drawn even closer together, would be the last thing one wants in clay.
But at the molecular level, the problem is not that the distance between clay particles is too small for good soil structure, but that it is often too uniform. These particles tend to distribute themselves evenly in space partly because they are negatively charged and therefore repel each other. In contrast, sand and silt are electrically neutral and have no particular tendency to pull together or push apart. Technically speaking, clay tends to disperse rather than to aggregate.
Calcium and magnesium help overcome clay’s dispersion because they are positively charged divalent ions, i.e. atoms missing two electrons. Their positive charge means that they are attracted to negatively charged particles such as clay. And because they have a double charge, these divalent ions can act as “bridges” between clay particles, forming an electrical attachment with two different particles. As a result, they help draw negatively charged clay particles together, aiding in soil aggregation. Since humus particles, like clay, are negatively charged, calcium and magnesium can also bridge the gap between a clay particle and a particle of humus, thus incorporating humus into soil aggregates.
Like magnesium and calcium, sodium is a positively charged ion (a cation), but unlike them it is monovalent, meaning that it has only a single electrical charge. (It is missing one electron.) Because it is monovalent, a sodium ion can only form a bond with one clay or humus particle. It has no second charge with which to bind to another particle. Sodium’s monovalence also means that more sodium cations than calcium or magnesium cations are required to fill the bonding sites on a clay particle. This results in a thicker layer of ions around the particle, “pushing” it further away from other particles.
Unlike magnesium and calcium, therefore, sodium does not aid aggregation, and when it builds up in soils, replacing divalent minerals at clay binding sites, it actually damages soil structure. It causes aggregates to break down and clay particles to disperse, clogging the remaining spaces in the soil. Furthermore, now that the magnesium and calcium cations are no longer bound to clay or humus, they leach from the soil, leaving it less fertile.
Gypsum acts on these soils by adding calcium, which competes with the sodium for binding sites on clay. Calcium, being divalent, draws soil particles together, beginning the process of soil aggregation. Now it is the sodium that leaches from the soil.
Soils in the eastern half of North America are unlikely to be sodic unless they have been heavily treated with synthetic fertilizers heavy in sodium. Western soils usually have higher concentrations of salts, including sodium, so they have a greater tendency to sodicity.
The action of gypsum is so complex and conditional that it makes sense to have your soil tested for salinity and sodicity and to discuss your situation with a county extension agent before using gypsum to flocculate clay soil. Nevertheless, here is a chart outlining various uses for gypsum and when it has what effect.
|Will gypsum —|
|raise pH?||In normal soils, only if it contains magnesium. In some acidic soils of the US southwest, yes, because of complex chemistry of aluminum.|
|reclaim alkali (sodic) soils?||Yes, if those soils are also low in other salts, if sufficient quantity is applied, and if pure (non-saline) water then leaches out the sodium.|
|flocculate (loosen) clay soil?||Yes, if the soil is sodic and all the conditions just above are satisfied. This is equivalent to reclaiming alkali soils.|
Here are some guidelines for using gypsum:
• As with sand, do not rely on gypsum alone as a flocculant. For one thing, gypsum is so fine a powder, it is hard to distribute effectively. Mix it with compost and either apply both as a top-dressing, or dig both in together.
• Check on the source of your gypsum, and in general only use natural gypsum, not recycled or dry-wall gypsums, which can contain various impurities.
• If your soil is low in magnesium, it’s a good idea to add some when you use gypsum, as the calcium in gypsum competes with magnesium and can cause it to leach out of the soil. Gypsum with dolomite in it may solve the problem, unless your pH is already high.
• Do not overuse. Too much calcium can make important trace elements, as well as magnesium and potassium, unavailable to plants.
• To determine whether gypsum will be effective in your soil, you can use the Emerson Dispersion Test, which you will be happy to hear is remarkably simple. Drop a small lump of soil (maybe half an inch or 6 mm in diameter) into a glass of water, and then don’t move it for 24 hours. Check it after one day. If the clay is unchanged, don’t bother with gypsum. If, however, it has begun to dissolve, softening at the edges, or even flattening into a disk, then add gypsum. Since interpretations can vary, it’s still a good idea to talk to a knowledgeable local.
• Above all, before you buy gypsum, check where it comes from, what other chemicals it contains, and what effect they may have on your garden. Remember that only gypsum that contains dolomite or some form of lime will raise pH levels.
To overseed means just what it says, to sow seed directly over other grass. This is a particularly effective method to improve a lawn when grasses are thin or patchy, but it can also be used to gradually replace a poorly suited grass with one better-suited to the region.
While overseeding your lawn can be effective anytime during the growing season, it’s far better to wait, and to do one’s seeding in spring or fall, not the middle of summer. September is ideal in most of North America, as the new grass has a chance to get established before the spring rush. For planting you want weather still warm enough for seeds to germinate (70 degrees F.), but cool enough so that they can’t dry out or get cooked where they lie.
If you’ve got a standard-issue lawn, chances are good that the grass itself is not one best-suited to the region where you live, which makes all lawn care a challenge, organic or not. Overseeding lets you add a better-suited grass to your lawn without requiring that you start over from scratch.
The goal here is to expose as much soil as possible without tearing up the grass you have, so that the new seed will be able to reach the dirt. The basic steps have asterisks. If you add in the others, you get what one pair of experts (Nancy Szerag and Jeff Ball) call the “Cadillac version.”
With that in mind, follow these steps:
Weed thoroughly. Once you’ve seeded, you won’t be able to do this for several weeks, so doing it beforehand is worth the time. Weeding will give the new grasses more space and less competition.
*Mow your grass as short as your mower will allow, even if you hit bottom from time to time, and collect the clippings. (Yes, here you get to do TWO things that are usually forbidden.) Short grass will give seeds better access to the soil below and more light once they sprout. It will also stress the old grass a bit, giving the new type a fighting chance to establish itself.
*Remove thatch; bare the soil. For seeds to take root in soil, they must touch it. A thick layer of thatch can be a major obstacle to successful overseeding, so if your thatch layer is thick, you’re going to need to get rid of it. If it’s light to non-existent, you may only need to rake briskly with a garden rake. Using a slice-seeder can eliminate this step, as the seeder actually cuts through thatch into the soil and deposits seed.
Aerate if you can. Both the loose soil plugs and the holes provide ideal sites for germinating seeds. Furthermore, since aerating helps improve soil, doing it will give grass seed an ideal start. When you’re done, you should have 6 to 12 holes per square foot. The easiest way to get this is by aerating in more than one direction. Move horizontally across your lawn, then vertically, then diagonally. The lawn will be a mess, but it’s all good. Those little plugs will simply disappear in a couple of weeks.
Amend the soil with a mixture of peat moss or coconut fiber and compost. Nancy Szerag and Jeff Ball, at the Yardening and Gardening blog post mentioned just above, suggest 3 bales of moss or fiber and 120 pounds of compost for every 1000 square feet. They also have suggestions about additional amendments.
Seed thickly. A number of different sources recommend seeding much more thickly (up to one and a-half times) than recommended for whatever seed you’re using. This is particularly good advice if you’re trying to replace one type of grass with another. The undesired grass already has a serious head start, and over-seeding (seeding too much) can help to correct that discrepancy. Since most grass seeds will have instructions for both overseeding and for seeding a new lawn, one option is to seed at the new-lawn rate, rather than the recommended over-seeding rate.
Tip: Spreading seed alone can be a tricky proposition. Mix the seed with sphagnum peat moss, coconut fiber, sand, or compost, then seed.
Use a slice-seeder. As mentioned above, a slice seeder cuts through thatch, depositing seed directly into the cut. This mechanism ensures that seed comes into contact with soil and helps ensure that seed gets spread evenly.
Cover the lawn several times. To get an even distribution, divide the seeds into two to four packets and seed each while moving in a different direction or pattern across the lawn. If you’ve only got time or patience for two passes, divide the grass seed in two, and seed once moving back and forth in parallel paths across the lawn, and the rest moving at right angles to the first pass.
If you can, make three passes. Divide the seed in three and seed once vertically, once horizontally, and once diagonally.
For best results, topdress lightly (about a quarter of an inch, not more) by sprinkling compost, topsoil, peat moss or coconut fiber over the newly seeded lawn. (A roller spreader makes this quite easy.) The soil amendments will give the seeds a boost and will help retain water over and around the seeds.
Alternatively, rake lightly to work the seed into the soil.
Roll the lawn if you want a perfectly level surface, but use a roller only half-full of water.
Keep the soil surface damp while seeds are germinating (which may take as much as two weeks) and while seedlings are young and new. Most experts say this means watering twice a day until seeds sprout and once a day for at least a couple of weeks afterwards.
Mow when new grass is 2-3 inches high.
Organic lawn fertilizers are slow release, meaning that they work gradually. Quick-release synthetic fertilizers are chemically simple and become available to a plant easily and all at once, so they don’t last very long.
Think of the difference between popping popcorn and boiling water. When you boil water, unless you have a really weird stove or a very strange pot, all of it is at just about the same temperature, and it all starts to boil at the same time.
Popcorn, however, does not all pop at the same time. Even if you’ve got only one layer of kernels and they’re evenly spread across the pan, some will pop before others. A graph of the popping cycle probably looks like some sort of bell curve: first just one pops, then a couple, then several, and more and more, and suddenly you’ve got a rush, and a lot popping all at once, and then the rate drops off, first pretty steeply and then more gradually. (Which is why some of us consistently burn our popcorn: we’re always waiting for that last kernel to pop.) This is like a slow-release fertilizer, though with a good one the rush and roar are somewhat diminished, and the whole process takes a couple of months, not a couple of minutes.
Quick release may sound like a good thing, but the problem is that it’s over quickly. A second analogy may make this clearer. Think of a light bulb, which releases energy, in the form of light, for quite a long time, at a steady rate. That’s your slow-release fertilizer. Quick release, however, is more like an explosion. There’s a sudden release of energy and light, but then it’s gone. If you’re trying to knit, read a book, or build a cabinet, the light bulb is a lot more useful.
1) Locate a SLOW-RELEASE organic fertilizer that’s easy to use and especially rich in nitrogen (rather than in phosphorus or potassium, the other key chemicals in fertilizer). Blood meal (12% nitrogen), corn gluten meal (9%), and cottonseed meal (6%) are all good choices. Liquid fish emulsion is an excellent plant food, high in nitrogen, but it isn’t slow-release. If you use it for your first stage, you will need to follow-up within a week or two with another dose.
2) Follow the directions for your chosen product to determine the appropriate amount for your lawn. Apply it evenly over the grass in the late afternoon or evening, or in the morning just before you water.
3) Sprinkle a quarter to a half-inch or so of coconut fiber or peat moss over the fertilizer.
4) Water thoroughly, before sunlight reaches the treated areas.
CAUTION: Follow directions and do NOT over-apply nitrogen products, as they can “burn” your plants, leaving them brown and, well, dead.
Do NOT apply nitrogen fertilizers in the middle of the day, especially in the sun, as the sunlight will exacerbate the burn, making your grass, once again, vulnerable to death.
Reasons and Rational:
Why water? Watering will wash the nitrogen off the leaves of the plants and down towards the roots, thus protecting against burn (and death). Getting the stuff off the leaves doesn’t ensure that plants won’t be damaged, but it does help. Watering also keeps the layer on top (the coconut or peat moss) from just drifting away on the next breeze.
Why sprinkle coconut fiber or peat moss over the nitrogen product? You don’t have to. But there are a couple of good reasons for doing so. First, it shades any exposed areas, thus helping to prevent burn. Second, it’s good for your lawn anyway, as it adds organic matter (but not nutrients) and helps to hold water.
Why coconut rather than peat moss? Because peat moss, which comes largely from northern Canada, is harvested in vulnerable wetlands by large-scale machinery. Though not a non-renewable resource, it does take centuries to form, while coconut fiber, or coir, comes from a more renewable resource, the husks of coconuts.