For a gardener weary of winter, the countdown to spring is a tale told on the backs of seed packets. That magical last day of expected frost may be months away, and even a future in which the soil can easily be worked is a distant hope. But meanwhile, the envelopes have arrived, with their soft rattles and swishes, bursting with latent promise. I collect them all into stacks—those to be started 8 to 10 weeks before the last frost, then the 6-week ones, then the tropical 4-weekers—securing each stack with a rubber band. This gives me a program. Next, I start rounding up all my gear.
Seed-starting equipment has come a long way since the days of egg cartons and cutdown milk containers, though there is certainly nothing wrong with either of those methods. As with any aspect of gardening (or life), you can be as homey or as high-tech as you please. Seed and tool companies carry plastic flats in many shapes and sizes, some of them modular systems complete with transparent plastic lids or domes that keep the soil from drying out. (Use these lids with caution, lest you overheat your seedlings.) You can broadcast seeds into a small tray, one variety per tray, or in rows in a larger one. Some come premolded into straight furrows. But essentially, any well-drained container will work, if it holds two and a half inches of planting mix with a bit of space to spare. Use some of that pre-spring energy to clean them thoroughly with a solution of one part bleach to ten parts water, to help prevent damping-off.
You need to have other containers cleaned and ready to receive your seedlings as soon as they can be transplanted. There are many styles of preformed plastic flats, divided into compartments, as well as various individual containers, from plastic pots to eggshells. Peat pots are handy, but they don’t decompose as well as they are supposed to. You can strip off the top edge, rip off the bottom, and score the sides to encourage the roots to come through, but this defeats the purpose of a rather costly product that you must restock every year.
My own favorite method is to use a soil block maker, a system sold by Johnny’s Selected Seeds and Territorial Seed Company. With these beautifully made gadgets, you can form your starting mix into sturdy cubes that produce plants with excellent root systems. You’ll need at least two sizes. One makes 20 miniblocks, each a three-quarter-inch cube with a small indentation on top to receive the seed. The other makes four two-inch cubes for large-seeded plants, or to receive seedlings started in the smaller blocks. Ingenious cube inserts can be put into the larger block to create holes exactly the size of the miniblock. By transferring a newly germinated seedling in its miniblock into the hole in a larger soil block, you avoid transplanting shock altogether.
With either blocker, the cubes are made by plunging the device into a tray of starting mix that is just moist enough to hold together. For germination, I use a soilless, peat-based product such as Pro-Mix BX, because it contains a better quality peat than I can buy myself. Recently, I have avoided formulations that use vermiculite, because of concerns about its asbestos content. For transplanting, I enrich the mix with sifted, mature compost. I sow seeds singly into the miniblocks, even small ones, shaking them carefully out of a creased seed packet. I mark the date and variety on a wood or plastic label with a waterproof pen.
I don’t cover the seeds with soi except for the few that need darkness to germinate, such as delphiniums. I don’t wait for the first true leaves to appear to transplant my seedlings, as most books recommend, but instead as soon as I see a speck of green. This impatient course, which was originally promoted by the great British horticulturalist William J. C. Lawrence in his 1948 book Science and the Glasshouse, produces excellent results.
Potting soils today aren’t made of soil at all. They are in fact soilless mixes. So what exactly do they contain? Here’s a quick rundown of the basic ingredients and their purpose.
Sphagnum peat moss: Decomposed sphagnum moss: retains water extremely well; has a low pH.
Vermiculite: Mica expanded by heating, which allows it to hold largc quantities of water. Comes in varying size grades. No. 2 is the basic horticultural grade, while the finer no. 4 is used in seed germination. Make sure you buy the horticultural grade, not the construction grade used for insulation.
Perlite: Natural volcanic material that has been steam-expanded. Provides excellent drainage and is inexpensive. Particle size of 1/16 to 1/8 inch is usually used.
Wetting agents: Surfactants that prevent water from beading up on the surface and encourage water absorption.
Fertilizers and trace elements: These are often added to soilless mixes; for seed starting, you want a mix labeled “germination mix,” “starter mix,” or “plug mix.”
Lime: Ground dolomitic limestone added to offset the acidity of the peat, producing a near-neutral pH.
To this basic mix, the following are sometimes added:
Bark: Chips from softwoods such as pine or fir bulk up a mix and increase aeration. They are too coarse to use alone in seed starting.
Compost: Inadvisable for seed germination since it isn’t sterile.
Sand: Adds weight, but drains extremely well. Be sure to use sharp builder’s sand, not the kind from the beach.
Bottom heat will speed germination of seedlings, especially for heat-loving plants like melons. I like the safe, even heat provided by a rubber heat mat, one with a thermostat and a sensor that you stick into the soil. The top of the fridge, toward the back, is a nice warm spot, or on top of a cabinet near the ceiling. A temperature of 70 to 75°F is optimal. Be sure to check the flats at least once a day. They must not dry out. Moisten them with a fine spray that won’t dislodge seeds or soil. A spray bottle works fine for small flats, but you’ll need a watering can with a fine rose for larger quantities. In a home greenhouse, use a hose with a Wonder Waterer, a short wand that delivers a lovely soft spray and no heavy drips.
Once seeds have germinated, move the seedlings to a location where they receive bright light, good air circulation, and 60 to 70°F temperatures. If you don’t have a greenhouse or a south-facing sunny window, you may want to rig up a system of fluorescent lights, suspended a few inches above your seedlings. Ample light is important not only to speed growth but also to keep the seedlings from getting leggy, and the gentle warmth the lights give off may be all you need for germination and growth. You can buy a simple tabletop model or an elaborate tiered device, or build your own system. Even the under-cabinet fluorescent lights in your kitchen can be used if you raise your flats on blocks to get them close to the lights. Use a timer to provide your plants with 16 to 18 hours of fluorescent light each day.
The good news is that the best artificial lights for raising seedlings are the least expensive and most available fluorescent tubes. Standard “cool white” fluorescent lamps provide excellent light for foliage growth. These can be mounted in standard four-foot shop-light fixtures available from hardware stores, or ganged at a spacing of three inches between lamps.
When raising seedlings, intensity is more important than the precise wavelength of the light. Bulbs should be positioned no more than a few inches above the plants. For blooming plants, switch to the more expensive full-spectrum fluorescent lamps, such as Agrosun, Gro-Lux, or Vita-Lite Power Twist. Many commercially available lighting units, such as Hydrofarm’s Green Thumb system (above), are adjustable, so that as your plants grow, you can raise the lights.
Finally, keep a journal. A record of seed-starting adventures from years past will remind you of successes and failures, improve your timing, and help you choose which varieties to grow.