Seed-starting Basics

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Like many gardeners, I used a motley collection of wooden flats, purchased trays and household discards when I had a home greenhouse with plenty of space. Now, my plant-starting space is more limited, so my system consists of one or two 10-row, commercially made plastic flats — rather flimsy things with narrow, three-fourths-inch-wide rows. Each flat is set into a 12-by-22-inch plastic tray; the 10-row flats are perforated but the trays are not. Soon after the seeds germinate, I transplant the seedlings into individual cells in four-, six- or eight-cell market packs saved from nursery purchases and donated by friends.

With this system, I can plant 20 kinds of tomatoes by putting a cardboard separator in the center of each row, and because the sections are small, I waste less seed as I’m not tempted to overplant.

Homemade scrap wood flats can be any size that fits your available space, with two exceptions: Not too large or they’ll be too heavy to lift when full of soil, and no more than 2 to 3 inches deep. Deeper flats waste potting soil, and too-shallow ones limit root development and dry out prematurely. Leave one-eighth-inch spaces between the slats on the bottom of a homemade flat to allow for drainage. I usually line mine with several sheets of newspaper to keep soil from washing through the bottom wood strips.

PLANTING MEDIA

Now, fill those containers with growing media that will encourage germination and root growth. Because seeds need only moisture, warmth and air to germinate, they can be started in nutrient-free materials such as vermiculite, shredded moss (not peat moss, which is hard to moisten and tends to crust when dry, but moss collected from the woods) or a mixture of equal parts vermiculite, moss and perlite. Vermiculite is mica that has been superheated to the point of expanding into flaky granules; sometimes, it contains small amounts of naturally occurring asbestos, so keep it damp and use it outdoors. Perlite is heat-expanded volcanic rock.

Today, the easiest plan for me is just to plant seeds in purchased potting soil. In the past, I’ve used a wide variety of homemade media. Here are three recipes that work well, especially for use as growing media for transplanted seedlings:

• A mixture of equal parts screened finished compost and vermiculite.
• A mixture of equal parts finished compost; commercial potting soil; and perlite, vermiculite or sharp sand, or a mixture of all three. Use coarse builder’s sand; avoid seashore sand, which usually is too fine and packs too densely, consequently offering less room for air.
• For a completely homegrown mixture, I’ve used equal parts compost, good garden soil (both screened) and torn moss gathered in our woods.

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