mixes are available, but you can make one from equal parts of peat moss, vermiculite, and perlite. Add two parts of fully finished, good compost to this basic mixture if you want the potting soil to supply nutrients for the first few weeks. Although compost is not sterile, it usually contains enough beneficial microorganisms to combat injurious ones.
PLANTING SEEDS
Most seed packets carry instructions for planting depth and spacing. A general rule of thumb is to plant seeds at a depth that is two to three times their diameter. Tiny seeds (those of begonias or snapdragons, for example) can be mixed with sand to help separate them and make them easier to handle; sprinkle this mixture on top of the potting mix. Most tiny seeds need light to germinate, so it’s important not to cover them after planting. When you mist the soil surface to water them, they’ll work themselves into tiny niches that will keep them moist. Plant larger seeds in individual holes, or make furrows as you do in the outdoor garden.
Some gardeners cover their seeds with a thin layer of fine sphagnum moss to protect the seedlings from damping-off (a lethal fungal disease). Sphagnum moss has fungicidal properties. If you use it in your seed flats, make sure it stays moist at all times. When the moss dries out it becomes hard and stiff, and tender seedlings may have difficulty penetrating it. Although it was used to dress wounds during World War II because of its fungicidal properties, some people experience skin irritations if it gets into cuts or scratches; wear gloves when you work with it.
Temperature. The best temperature for germination varies from plant to plant. Generally speaking, tender (frost-sensitive) plants usually sprout best in warm temperatures of 70° to 75°F. Cool-season flowers germinate better in cooler temperatures around 60° to 65°F. Some plants need a period of freezing or cooling at temperatures of 35° to 40°F before they can germinate. Seed packets often supply this information.
Sow seeds that are large enough to easily handle one or two at a time into flats, cell packs, peat pots, or other containers of moist potting mix.
Carefully cover seeds that don’t need light to germinate by sprinkling fine, loose, moist potting mix over them to the correct depth.
Light. Seedlings need plenty of light as soon as they break through the soil surface. Fluorescent fixtures are the best way to supply light for indoor seedlings. Their light is very even, and the plants don’t need to be turned to grow straight. You can use special “grow light” tubes, full-spectrum daylight lamps, or a combination of warm white and cool white tubes. Set the lights on a timer so they’re on for 16 hours a day. The tops of the seedlings should be no more than 3 or 4 inches below the lights for the first couple of weeks; later you can gradually raise the lights to 5 inches above the leaves. Start out with the seedling flats elevated on some sort of stand that can be gradually lowered as the plants grow taller. (A pile of books works nicely.) Or suspend the light fixture on chains that you can raise or lower as the plants grow.
If you want to try growing seedlings without using artificial lighting, your best bet is a south-facing window covered with sheer curtains (to keep the heat from becoming too intense) or a bright, unshaded east or west window. Turn the flats every day to keep the stems growing straight.
Water. Seeds and young seedlings need to be watered carefully so that the seeds aren’t washed out of the soil and the delicate new roots aren’t disturbed. The best approach is to water from below, setting the flats or pots in lukewarm water in a sink or special watering tray. Watering from below allows you to evenly and thoroughly moisten the soil without dislodging seeds or tiny seedlings, as can happen with a stream of water from overhead. Set flats or pots in a container of water an inch or so deep until the soil surface feels moist, or use a specially made flat and wicking mat. This method gives you the most control over the amount of water your plants receive. Another technique is to mist the soil surface with a plant mister until the soil is thoroughly moistened. If you use this method, be sure to keep an eye on the soil. Make sure your seedlings don’t dry out; water stress can set back young plants permanently, so you will need to be attentive until the plants are well established. But don’t overwater either. Constantly soggy soil encourages root rot and damping-off. Water your seedlings when the soil is somewhat dry—early enough so that leaves can dry by dark.
Fluorescent lights provide a very even light to plants. For best results, use a timer to keep the light on the plants for 16 hours each day.
Feeding seedlings
Because the soilless mixes for seed-starting contain almost no nutrients, you’ll have to supply some as soon as seedlings develop their first true leaves (the second set they form). But don’t go overboard; overfertilizing seedlings can result in weak, floppy plants more prone to problems. Young seedlings can’t handle full-strength fertilizer. Dilute liquid fertilizers to one-quarter the recommended strength (or if you use fish emulsion, half strength). Use the diluted fertilizer once a week for the first three or four weeks. After that, gradually work up to using a normal dilution.
If you’ve added compost to the seed-starting mix, you can probably wait to feed your seedlings until they are four or five weeks old. But check their color every day; at the first sign or yellowing or purpling, begin feeding once a week with a half-strength dilution of liquid fertilizer.
TRANSPLANTING PLANTS IN PEAT POTS
Seedlings in peat pots need special treatment at transplanting time; peat pots can be so rigid that roots have difficulty breaking through them. Set the pots in a water-filled tray for 30 minutes to an hour before transplanting. When you plant, tear through the sides of each pot, and place the seedling so that the pot rim is below the soil surface, left. You may need to tear off the top ½ inch or so; if the rim sticks out of the soil, it can dry and act as a wick, drawing moisture out of the soil and evaporating it into the air. On a sunny, breezy day this wicking action can cause serious water stress for young plants.
Harden off seedlings in a cold frame by opening the lid for a gradually increasing length of time over several days, finally leaving it open all night, middle.
Thin seedlings by snipping them off with sharp scissors instead of pulling them up to avoid disturbing nearby roots, right.
THINNING AND TRANSPLANTING SEEDLINGS
When the seedlings develop their first true leaves—the second set of leaves to grow but the first that have the plant’s characteristic shape—it’s time to thin. You can thin by pulling up unwanted seedlings individually, snipping off the stems at soil level with nail scissors, or carefully lifting and transplanting the young plants to other containers.
Spacing for seedlings in flats or pots depends on the size of their
