Know Your Lawn
“Dirt: The Ecstatic Skin of the Earth” – William Bryant Logan
Soil consists of rock particles (sand, silt, or clay, in descending order of size) plus organic matter, as well as the air and water that move in the pores between these solids, and perhaps most important, the animals, microbes, and fungi that live in the mixture. Most of us do not think of the dirt beneath our feet as living, yet it supports an extraordinary array of living creatures. It is these living creatures within the earth, from earthworms to micro-organisms, that help to decompose organic matter and thus make soil capable of supporting life above the earth (see Healthy Soil, Healthy Lawn).
A full description of the topsoil in a particular location would include soil texture (what size are the rock particles?) its structure (how do those particles clump or aggregate?), its density (how compacted is it?), its pH (how alkaline or acidic is it?), its mineral content (what nutrients does it contain? what toxic minerals, if any?), its organic content (how much organic matter does it contain?) and its depth. And that is just the topsoil.
Texture, structure, and density together determine how porous a soil is and thus how easily water and air move through it. pH and mineral content influence fertility, or how many nutrients are present in the soil and how easily plant roots can absorb them. The first three topics, in other words, deal with the physics of soil, while the next two have to do with its chemistry. The sixth topic, organic content, influences both physics and chemistry of the soil, while the last attribute, soil depth, is in many senses the simplest of these concepts, dealing not with soil quality, but with quantity.
Texture in the soil refers to the size of the mineral particles in soil — the relative amounts of sand (coarsely ground rock), silt (medium-fine rock particles) and clay (finely ground rock). The pores in very sandy soil can be so large that water quickly drains through it, falling beneath the reach of plant roots. On the other hand, fine clay particles tend to form a dense, non-porous soil that is poor in oxygen, absorbs water only reluctantly, and then holds onto it tenaciously. The following table indicates what percentage of each is present in different types of soil. Loam, at 20% clay, 40% silt, and 40% sand, is generally considered ideal for growing.
Soil structure deals with how the particles in soil clump, or aggregate. Structure can be described as platy, prismatic, columnar, blocky, granular, or, get this, structureless, but despite the undeniable appeal of these terms, they are not central to our purpose here, as we are concerned not with the exact form that soil structure takes but with what it is and what influences it.
The various solid components that make up soil — the rock particles and organic matter — tend to aggregate, or come together, in irregular bundles, called peds. Many factors, including soil texture (the average size of the rock particles in the soil), type and amount of organic matter, pH, and salinity, influence how these components aggregate. In turn, the resulting structure helps determine many other factors, including drainage, density, and aeration, which in their turn influence how deeply roots grow and how easily they take up nutrients. Soils with good structure are described as being “in good tilth,” a term related to “till” and “tillage,” and used to indicate soils that are ready for crops or other plantings.
The purpose of soil amendments (as opposed to fertilizers) is to improve soil structure. Fertilizers add nutrients to soil; amendments balance the pH and improve the circulation of air and water. These things determine how easily plants can make use of whatever nutrients are present.
Ideal soils have the following characteristics, all of them dependent on structure:
• They are highly porous, so that they contain large amounts of air (up to 25%) and are easily permeated by water; yet they are also absorbent, so they retain water when wet. (Sandy soils are porous but not absorbent; clay soils are not porous, but they are highly absorbent, in this specialized sense.)
• They are friable — easily crumbled by hand into smaller particles. Sand is not friable because it has no structure to crumble; neither are clays, which resist crumbling, being hard when dry and sticky when wet.
Neither clay nor sand tends to aggregate easily, which is one reason why neither is satisfactory as a garden or lawn soil. Pure clay and pure sand are the structureless soils. In both cases, the addition of organic matter (compost!) helps enormously.
Compost improves soil structure not only physically, by adding absorbent material to sand and porous material to clay, but chemically as well. In clays, organic matter contains long molecules that help bind clay particles together into peds. In sandy soils, negatively charged particles of humus provide binding sites for positively charged ions of magnesium and calcium, thus preventing those nutrients from leaching away; the ions, in turn, bind humus particles together, aiding in aggregation. Compost also contributes microbes and other organisms, which have their own role to play.
Living creatures help to maintain and improve soil structure in ways too numerous to count, both chemical and physical. Here are just a few of those ways: Microbes decompose organic matter, producing compost; worms feed on that compost and produce, with their castings, the richest compost of all; worms and others move in the soil, mixing different levels and aerating as they go; all, in the end, contribute their bodies to the organic matter in soil. Healthy soil is impossible without these beings, most of them too small to see without a microscope.
Yet another key factor in soil structure is the chemistry of salts. Some of this is described in the discussion of gypsum. (See The Special Case of Gypsum). Loosely (very loosely) put, a number of key nutrients (primarily ions of magnesium and calcium) can bind to more than one particle of clay or humus, so they can actually pull particles together, helping aggregates form and thus improving soil structure. Other ions, and the key culprit here is sodium, can only bind to one particle, so they inhibit aggregation. When sodium levels rise too high, sodium ions displace magnesium and calcium, damaging soil structure and creating what are known as sodic soils, which have very poor structure.
Each of these factors — compost, living organisms, salts — plays a more involved role in soil structure than that described here. This overview, however, gives some idea of how complex soil structure is, and how central it is to plant health.
Healthy earth is porous; compacted earth is not. Neither air nor water move easily through compacted earth, and even earthworms can find it tough going. Roots themselves have a harder time moving through tightly packed dirt, and the lack of oxygen and water make nutrients harder for roots to access.
Compacted earth is therefore a serious problem for lawns and one that needs to be corrected if the grass is to be truly healthy. The single most important treatment is aerating, but best results are achieved through a combination of approaches. Aerating, amending, and topdressing all help.
pH is a measure of how acidic or alkaline soil is, conditions which help determine plant health and happiness. It’s measured on a scale of 0 to 14, though if your results are anywhere near either of those numbers, you probably can’t grow anything at all — but you might be able to sell tickets to soil scientists, curious to see this phenomenon.
Tip: The Rapitest pH Soil Tester is designed for simplicity of use with accurate results. For those of you new to soil testing, you’ll appreciate this easy, fast and fun way to achieve better growing results from your lawn and gardening efforts!
Chemically, pH is a measure of the presence of free hydrogen ions in a solution. ‘Free’ here means “free to bond with other ions,” while the solution, in the case of soil, is always a water solution. The hydrogen atoms in water are in constant motion, leaving water molecules and then recombining with them hundreds of times a second. When a hydrogen atom breaks its bond with a water molecule, it leaves its electron behind, becoming a positively charged ion. The water molecule it left, now known as a hydroxide ion, has an extra electron, so it is negatively charged. In a pH-neutral solution, the concentration of hydrogen ions (H+) is equal to that of hydroxide ions (OH-). A greater concentration of hydrogen ions yields an acidic solution; a greater concentration of hydroxide ions yields a basic solution. (Basic and alkaline are not synonymous, but the distinction isn’t important here.)
On the 0-to-14 pH scale, the middle number, 7, is neutral. Lower numbers indicate acids and higher ones basics. It’s important to know that this is not a linear scale, but a logarithmic one, which means that each number on the scale indicates a ten-fold increase in the concentration of hydrogen ions over the number above it. A solution with a pH of 6 has ten times as many free ions as one with a pH of 7; a solution with pH 5 has a hundred times as many.
Soil pH frequently affects how minerals behave or what form they’re in, and thus how easily plants can absorb them. There are no simple summaries of these effects, as change in pH often initiates not one chemical process but several, even for a single nutrient. Just as an example, five of the seven micronutrients — manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), and boron (B) — become increasingly unavailable as pH rises. This results not from a single process, but from several, which include the formation of less soluble compounds, conversion to ionic forms not usable by plants, and an increase in bonds to negative soil particles (clay and humus). Zinc and copper are both affected by all three.
As a result of such chemical processes, nutrients can be present but unavailable to plants; they are said to be tied up. Other minerals (including a number of nutrients) become increasingly tied up as pH falls. Neutral or slightly acidic pH generally allows an optimal range of nutrients to be available to plants.
All plants need varying amounts of the three primary nutrients in most plant foods, nitrogen (N), phosphorus (P), and potassium (K), and smaller amounts of the secondary nutrients calcium (Ca), magnesium, (Mg), and sulfur, (S). Beyond that, they need trace amounts of seven micronutrients boron, chlorine, manganese, iron, zinc, copper, and molybdenum.
Both excesses and deficiencies of nutrients can cause problems. It’s axiomatic that deficiencies of necessary nutrients would cause problems, but not obvious that excesses would. If two chemicals behave the same way chemically — binding to the same sites on the same molecules under similar conditions — an excess of one can mean that it beats out the other in the chemical bonding game. The excess of one nutrient, then, can cause a deficiency of another. In other cases, excesses themselves can be toxic, for several of these minerals, such as chlorine and copper, to name two obvious examples, are poisonous to both plants and humans in sufficient quantities, though they’re essential in small quantities.
Different soils supply different amounts of these nutrients, so if problems appear it helps to get your soil tested.
Nothing, but nothing, can substitute for organic matter in soil. That matter can be present as living, dead, or decomposing organisms, or as humus, the final, most stable stage of decomposition. According to William Bryant Logan, author of Dirt: The Ecstatic Skin of the Earth, no one quite knows what humus is, a curious statement on the face of it. Apparently humus molecules, while sharing certain properties, differ slightly each to each. Logan quotes two soil scientists, one of whom sighs, “Humus is imperfectly understood,” while the other states that “It is very possible that no two humus molecules are or have ever been alike.”
In his book Life in the Soil, James B. Nardi takes up Logan’s implicit challenge, defining humus as such “hard-to-digest plant materials” as “oils, resins, lignins, and waxes” that have already passed largely unchanged through at least one decomposer, an animal or organism that feeds on dead organic matter. These organic materials can take hundreds of years to break down into their constituent elements, and in the meantime, they play essential roles in building soil aggregates and in the complex chemistry that makes elements available to plants.
Compost contains decaying matter at a number of stages, and even when it is mature, it consists of a huge spectrum of organic constituents, humus being only one. The chemical diversity of organic compost makes it profoundly different from any other soil amendment. So does the rich array of living organisms within it. These two things in part explain why compost is so adaptable, so widely useful. No matter what soil problem you’re facing — pH imbalance, too much sand, too much clay, compaction, nutrient poverty, thin topsoil, poor structure — compost will help. It may not solve the problem, but it will always help.
Compost contains millions of micro-organisms, the microscopic beasties that do the work of breaking down dead organic matter into humus. When you add compost to your soil, then, you are also adding the micro-organisms that produced it. These micro-organisms can then go to work in your lawn, turning grass clippings and thatch to soil, making nutrients available to your grass, and in the end adding their bodies to the compost in which they lived. Compost also provides the food for earthworms, whose castings are the best compost of all, whose tunnels aerate soils, and whose presence alone provides a good index of the health of a soil.
Depth brings us back to earth: it’s all very well to go on about lovely humus-rich dirt, but if there’s not enough of it, you’ll have problems. It’s rare, though, that you’ll have a thin layer of rich earth. So if your top-soil is thin, take hope; as you improve it, it will get thicker. This is one case in which it’s possible to kill two birds with one stone.
If you’re starting a new lawn, depth is something you can test and correct before planting seed or laying sod. If you’re improving an established lawn, you can add an inch or so of soil as an amendment each spring and fall, until your soil reaches the desired depth. Eight inches is generally considered adequate; twelve is good; twenty-four is a rare treasure.
The Way of Water
How It’s Lost
Starting with the obvious, let’s state that you put water on grass to water the grass, not to raise the water table, rinse your driveway, or augment the neighborhood stream. Lawn sprinkling water which does not end up in the grass has been wasted (see Water Saving Tips For Lawns).
In the grandest scheme of things, of course, nothing is wasted; the principle of the conservation of energy sees to that. On a slightly more local, planet-wide level, the water that evaporates in Texas does fall as rain somewhere else on earth. But most of us live on a more human, less metaphysical scale; as the Ogallala aquifer under Texas (and New Mexico, and Oklahoma, and Nebraska, Kansas, Colorado, Wyoming, and South Dakota) falls, the fact that its water reaches earth again as rain in the Atlantic ocean, or as snow in Iceland, offers little comfort.
Water can be lost through four routes:
1.) percolation, when it sinks through the earth below a level to which plant roots can reach;
2.) transpiration, the “breathing” of a plant’s leaves;
3.) evaporation from the surface of the soil itself, and finally
4.) run-off, where it moves across the surface of the earth, often to a body of water, instead of sinking into the soil.
Using Less on Your Lawn
The first, the most fundamental way to reduce the amount of water your lawn needs (beyond shrinking the size of the lawn) is to have the right grass, because one of the things that makes a grass appropriate is that it doesn’t need much more water than whatever falls as rain. Native grasses, while not the only option, are usually strong candidates, because they’re adapted to the normal rainfall of the region. Most natives, though, do yellow in August, so even they will need supplemental watering if they’re to stay green through the end of summer. However, Kentucky bluegrass can use twice as much water as some fescue mixtures, so the water difference is not trivial. (See The Special Case of Kentucky Bluegrass, at the end of this page.)
Beyond lawn size and grass selection, several watering techniques can cut the amount of water required to keep a lawn green. These include equipment, timing, frequency, and duration.
Equipment: Drip systems, which deposit the water almost directly into the earth, will almost always use water more efficiently than sprinklers, which spray water into the air. However, drip systems don’t generally work out too well for lawns where mowers are used, so the goal must be to find as efficient a sprinkling system as possible.
Consider droplet size. The finer the spray, the more water is lost to wind and evaporation. However, watering equipment that create big rather than fine drops tend to lose more water to percolation and run-off, because they dump too much water on the ground for it to absorb at one time. They also tend to leave gaps between soaked areas, with two possible results, neither of them good: either people leave them on for a longer time, so that the under-watered areas finally absorb moisture from the over-watered areas around them, or some parts of the lawn remain under-watered. Clearly, it’s important to find a sprinkler that gives a middle ground between a fine spray and large drops.
Other factors influence sprinkler evaporation as well. Both speed and distance play a role. The further the drops travel, the longer they are in contact with the air, and the more evaporation can take place. As a general rule, then, sprinklers that send the water out horizontally will lose less to evaporation than those that reach a similar area but which spray to a greater height.
The weather, especially temperature, humidity, and wind, all affect evaporation rates. Using the system on a hot, dry, windy day obviously maximizes evaporation, while watering instead in the cool of the day (early morning or early evening) when there isn’t much wind minimizes it.
The timing, frequency, and duration of home lawn watering will also influence water use. Watering in mid-day is most wasteful, of course, since this is when temperatures and evaporation are highest, and plants’ ability to absorb and retain water is lowest. Frequent, brief waterings will require more water in the long run, because they prevent grass roots from growing deep and thus becoming drought-resistant. Therefore, though deep, infrequent watering uses more water at any one time, it uses less over a season because it trains grass to dig deep for moisture. This method also cuts back on evaporation, since the surface of the soil and of the grass blades themselves will be wet for less time than if the grass is watered frequently.
Tip: The Galcon 9001 (shown at left) is a state of the art automatic irrigation controller designed for residential use. The easy to use six button programming system enables you to set each day individually or program the week as a whole. Easy to use — no plumbing required!
But deep watering on dry earth has its own drawbacks, as it can lead to loss through percolation or run-off. Think of dry dirt as a dry sponge: water rolls right off it. If you want to mop up a spill, you need a damp sponge. Dampen the earth before watering deeply, and it will absorb more water and hold it longer. Do this by watering twice, with a pause between rounds to let the earth truly absorb the first round, so it can better absorb the second.
Here, then, is the ideal watering regime: Water for half an hour early in the morning, until about half an inch of water has reached the ground. Wait an hour. Then water again until a full inch has fallen. Of course, you’ll need to adjust these numbers to fit your grass and soil type. Fescues, especially in the shade, will need less; Kentucky bluegrass, especially in the sun, will need the full treatment.
Less Lawn, More Garden: Breaking the Grass Habit
The ideal front yard of the fifties presented an uninterrupted sweep of grass from curb to front steps. Far more variety in landscaping is now tolerated and even encouraged. Creative landscapers sometimes maintain only enough lawn to provide views and walkways between garden plantings, and some walks may be planted in groundcovers other than grass. A shady walkway that doesn’t get heavy use can have a groundcover of moss or of creeping thyme, for instance.
A number of such Lawn Alternatives are listed in their own section; many more are available on the Web or at most libraries.
Going All Out: Xeriscaping
Myths and misconceptions abound about xeriscaping, starting with its spelling. You may sometimes see “zeroscape,” a misspelling that probably arises from “zero watering.” But “zero” is another myth. Developed in the eighties in Colorado, the xeriscape approach is frequently taken to mean a garden that requires no watering whatsoever. However, according to Judy Sedbrook, Colorado State University Master Gardener, of Denver County, “xeriscape means ‘water conservation through creative landscaping.’”
A xeriscape garden then, requires little or no water beyond rainfall, and it does not depend on a traditional mown lawn as a centerpiece. “Creative landscaping” invites us to think outside that box. The xeriscaped garden is designed and built to save water.
But xeriscaping does not require replacing your entire lawn with cactus and other desert plants, unless you live in the Southwest. It doesn’t necessarily mean going native, though frequently it works best with native plants, simply because they are adapted to the amount and timing of the region’s rainfall, and to each other.
It does mean having grass where grass makes sense and putting something else in areas where grass won’t thrive. For example, plants that require a lot of water do best in low-lying drainage sites or next to downspouts. Plants that crave coolness — sweet woodruff and coral bells — do best with an eastern or northern exposure or in shaded areas. When it comes to southern or western exposures, plants that love the sun, including Ice Plant, Snow-in Summer and Yarrow, would be good choices.
Another principle of xeriscape gardening states that grasses or plants that need similar amounts of moisture should be grouped together. This is one of the simplest ways to conserve water, because instead of watering heavily everywhere to satisfy the needs of a few water-mongers scattered throughout your garden, you only water heavily the few areas that need it.
Xeriscape principles can be applied throughout a garden, but they can also help solve problems peculiar to odd corners or niches. Here are some common problem areas for lawns, with common-sense Xeriscape solutions.
High Traffic Areas: Nothing looks worse than part of a lawn that’s been trampled down by repeated foot traffic. Instead of trying to revive the grass in those areas (probably a doomed proposition), consider putting in a walkway or patio. Another option is flagstone or open-work brick with a ground cover that will grow up and through the spaces in and between the bricks or stones (see Build a Perfect Path). Creeping thyme would work well in sun, moss in shade. After a season or two the ground cover will almost completely obscure the stones or bricks, which take most of the impact of traffic, thus preserving the “steppable” ground coves, as they’re called.
Heavily Shaded Areas: Grass craves sun, so why plant it where the sun won’t shine? Shade-loving groundcovers like vinca or sweet woodruff thrive under trees and on the north sides of structures. If you find out what natives grow in shade in your area and plant those, chances are you’ll have a very low-maintenance garden, instead of a struggling lawn.
Narrow Strips: Think about those islands of grass between the sidewalk and the curb, the driveway and the side of the house, a walkway and a fence. When you water these areas you end up watering the sidewalk, or the fence, or the side of the house. Remove the grass and replace it with drought-hardy plants and with drip irrigation, if necessary. This arrangement eliminates water waste and puts plants where they will thrive, not struggle.
Hard to Mow Areas: If you have a steep hill or an area with a lot of trees, it makes sense to plant something other than grass. Replace grass with ground covers (plant or gravel) or with low-water perennials.
Alternative Water Sources
Rain barrels can capture an extraordinary amount of water that otherwise goes to waste. Innovative folks have also trailed hoses from their bathtubs to the lawn outside, or even set up complex systems whereby household wastewater is filtered through a series of tubs and plant boxes before being collected in a tub for use on vegetables or grass.
All of these systems except the first, the rain barrel, are illegal in most places, since they circumvent plumbing designed in part to protect the public from water-borne pathogens and pollutants. One wonders, though, if legal versions of such arrangements will become available in the near, water-hungry future.
How Green Grows Your Grass?
For more details on specific grasses, see one of the websites listed in Sources and Resources under Identifying and Choosing Grass Types.
Grass is categorized in several different ways, two of which are summarized below. Knowing at least this much about grasses can help homeowners make intelligent decisions about what they want in their yards.
Creeping vs. Bunch Grasses
Creeping or running grasses spread a little as ivies do, sending out runners either above or below the surface of the ground. Nodes form along these runners where both roots and leaves can grow, forming a new plant. For a while the runner functions sort of like an umbilical cord, funneling nutrients to the “child,” but eventually the young plant takes root, becoming independent, and the runner dries up. Runners that move through the earth are called rhizomes; those that lie above it (like the runners of strawberries) are stolons. Both rhizomes and stolons, but especially the latter, can contribute significantly to the development of thatch.
Bunch or clump grasses have no such runners, but spread either through seeds or through what are called tillers, new shoots around the periphery of established plants that gradually increase their size. Since lawn grasses, being mown, rarely go to seed, bunch grasses used in turf tend to spread more slowly than do creeping grasses. Overseeding can help to develop the thick, lush grass that most people want in their lawns.
Warm Season, Cold Season & Transitional Grasses
Grasses are also categorized by whether they are warm season, cold season or “transitional.” Warm season grasses grow most vigorously in the hot months, going dormant (and brown) in cooler weather, while cold season grasses put on their growth spurts in spring and fall and go dormant during hot weather.
Transition Zone grasses are a mixture of warm season and cool season grasses that are designed for the states that lie between the south and the north extremes (i.e. Missouri, Kansas, Kentucky, etc.) Warm season grasses that do well in this zone include Bermuda and Buffalograss. Cool season grasses that are often used in this zone are Fescues, Ryegrasses and Bluegrasses. Most people tend to use more cool season than warm season grasses for transition zones.
Warm season grasses do well in the South, generally as far north as Tennessee and North Carolina. The most common warm season grasses in the U.S. include varieties of Bermudagrass and St. Augustine grass. Centipedegrass, Zoysiagrass, Bahaigrass, Carpetgrass, and Buffalograss are also frequently seen varieties.
Cool season grasses are planted throughout Canada and in the northern half of the United States, from Northern California and British Columbia east to Pennsylvania and Nova Scotia. Fescues and ryegrasses are gaining more and more popularity, especially as the disadvantages of traditional sod grasses become apparent. At least two companies (Bluestem Nursery Enviroturf in British Columbia, and Wildflower Farm EcoTurf in Ontario) have developed fescue mixtures specifically for northern climates. They do well in shade, remain green even when they go dormant during the hot summer months, and put down deep, drought-resistant roots.
The Special Case of Kentucky Bluegrass
“Kentucky Bluegrass is King,” announces Warren Schultz in his book The Chemical-Free Lawn. Such a statement shows how much has changed since the book was published in 1989, for now practically every organic book, pamphlet, or website preaches against the excessive maintenance costs of that King. Of course, kings are traditionally high-maintenance creatures, but twenty years ago a little extra water and a little more fertilizer did not seem outrageous. Even in western cities such as Calgary, bluegrass was the most prevalent lawn grass for decades, and it is still the only grass available there as sod (see Kentucky Bluegrass Lawn is not Environmentally Sustainable).
Why did it become so popular, so prevalent? It is almost infinitely adaptable, it roots and spreads quickly, and it works well as sod, whereas more deeply-rooted, water-saving fescues, for instance, don’t. (Such, at least, has been the received wisdom.) One has to wonder though, whether its prevalence became a function as much of inertia as of preference. Once the dark color of Kentucky bluegrass came to define what a lawn “ought” to look like, many people opted for it because it was familiar and easily available. Marketing thus played a major role, making bluegrass the only game in many a town.
Kentucky bluegrass is still one of the most widely available grasses in the U.S. and Canada, but standards have begun to change. It’s long been known that KB requires more water than most turfgrasses (if you want it to stay green through the summer, and most people do), but hard numbers comparing it to other grasses are only just becoming available. Tracy Dougher, a turfgrass and native plant specialist at Montana State University in Bozeman, has conducted experiments documenting the water needs of various northern turfgrasses. Her results, which will probably be published sometime in 2008 or 2009, show that in drier northern climates, one can cut water use in half by replacing Kentucky bluegrass with other grasses such as sheep’s fescue. (Conversation with the author, 4/21/08.)
Even the long-standing belief that more drought-resistant fescues can’t be grown as sods is being challenged these days. Dougher’s next project is a multi-year attempt to grow fescues as sod grass. Seeding will take place this spring, and the first sod will be ready to cut in the fall of 2010. If this is successful, homeowners in northern communities should eventually have a sod alternative to Kentucky bluegrass.
Once seen as a grass for all regions, Kentucky bluegrass may be on its way to being deposed, except in those high-rainfall areas where its rule is legitimate.