We’ve been browsing through the seed catalogs that are trickling in, not all of them in the mail, and scribbling down names of some new choices we might try. Our big annual order, full of old favorites, will get sent in a couple weeks. But seeds aren’t the only thing we’ll need.
While we consider which seeds to order, we also take stock of what we’ll need to get them growing fast. We’ve talked a lot in the past about ways to keep your starts healthy and from getting too leggy. And those things are important.
But the most important components of growing seeds indoors are the containers and the planting mix that will go into them. We’ve often found ourselves short of both when starting seeds indoors during the last weeks of winter and the first days of spring. List the things you need, whether potting mix or specialized flats and containers, then make sure you’ll have them on hand when it’s time to get those tomatoes started ahead of the last frost.
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Start with containers. Most of us are able to save many of them from year to year. But don’t use any that are dirty. Even the smallest bit of last year’s growing medium could harbor pathogens that might cause damping off, a common problem for the unlucky or careless gardener.
Any flats or containers you want to use should be rinsed completely clean. Some gardeners will soak the pots briefly in a five-gallon bucket of water to which a tablespoon or two of bleach is added. We’re aware of the personal and environmental risks of bleach and instead just leave our freshly scrubbed containers out in the sun. (Bleach is a severe irritant, both internally and externally, and can be deadly if ingested. If you choose to use it, be aware of splashing and other exposure and never let children handle it.)
We all know the “one pot, one plant” rule. While you may be tempted to scatter several seeds over the surface in a larger container, don’t do it if you intend to transplant. The roots will tangle when growing and you’ll most likely damage the starts when you try to separate them for planting outdoors. Having one plant in a container — it’s common to place three or so seeds in a pot before thinning all but the strongest after germination — allows you to take that plant’s root ball, soil and all, and stick it in the ground.
Those half-gallon milk container bottoms poked with holes (for drainage) will suffice again for tomato starts. We’ve learned over the years to cut them down a bit so as not to use so much starting mix. We also save the containers from flower and vegetable starts we buy at the nursery and we’ll recycle many of them by starting broccoli and other vegetables in them.
But, for efficiency and best growth, some starts require specialized containers. Going to start scores of onion seed indoors during February so you’ll have a lot of onion sets to put out in April, or maybe scads of geranium seed for a big floral display? Rather than start them together in long or big containers, start them in a seed plug tray that centralizes care and makes transplanting easy. If you’re starting plants like summer squash that don’t take well to having their roots disturbed during outdoor transplanting, try bio-degradable pots that are planted pot and all into the garden.
Whether you’re using milk cartons or commercial pots, consider the size of the pot before planting. Give them the room an depth to develop significant root structure. Will your be transplanting your starts, say tomatoes, from a smaller germination flat to a larger container before they go outside? When calculating the number of pots you’ll need be sure to make sure you have enough of each appropriate size.
Soft-sided, fabric “bag” pots that keep roots cool while inhibiting the roots’ tendency to circle are becoming popular with some gardeners. They, too, come in several sizes.
What you fill your pots with may be less important than you think. A North Carolina State University study found that seeds covered with vermiculite, peat or coir resulted in best germination rates and strongest growth (PDF). As long as what’s under the surface layer isn’t compacted, drains well, and contains no pathogens or non-organic materials, seeds will germinate and begin to grow true leaves without much in the way of nutrients in the soil.
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If you’re using a soilless potting mix that’s been sterilized, especially one made with lots of peat, make sure you give it a good soaking so it will absorb water. Wring it out well before using. It will stay just enough damp for planting.
When using vermiculite, be sure its certified for organic use. Some commercial vermiculite mines yield a product that contains asbestos. Make certain yours doesn’t.
Here, courtesy of Garden Betty, is a recipe for making your own starting mix. We like the way she keeps it simple.
If you’re going to keep those plants in the containers for a while, as you might with tomato starts, then make sure the starter mix will support the plants with the nutrients they need. If you’re using homemade compost in your starting mix, make sure its well finished. Unfinished compost might contain the pathogens that cause damping off. Sterilizing your homemade soil mix or compost in the oven to a temperature of over 160 degrees will kill the pathogens but all the beneficial organisms as well. And, baking compost in your oven makes your house smell like dirt.
Here’s some good, general advice (PDF) from Purdue University about what you’ll need to start seeds indoors. When to start your transplants? The University of Minnesota has a nifty chart (scroll down) for both vegetables and flower.
We’ve said elsewhere that a sunny windowsill isn’t enough for the kind of strong growth you want for your starts. And yes, a heat mat will give you faster and more consistent germination. But don’t forget the basics.
Eric is now retired, but is still a renowned gardener known for his expertise in composting, organic gardening and pest control, utilizing pesticide-free options, such as beneficial insects.
Eric believes when you do something good for the environment, the effects will benefit generations to come.
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