Lights or No Lights
Seedlings grown indoors often get spindly because they don't get enough light. You can start seedlings on a windowsill of a south-facing window or in a greenhouse, but in late winter, the days are still relatively short, so there is not really enough light to produce compact, healthy transplants. Seedlings raised on the windowsill will always be spindly compared to those grown in the South someplace and shipped north for sale in a garden center.
The best seedlings are grown under fluorescent lights. They give enough light to produce healthy strong stalky seedlings with very little trouble. For most people, just one shop light fixture with two 48-inch fluorescent tubes is sufficient to get started raising seedlings. Be sure the fluorescent light fixture is adjustable so that you can move it either up or down, or you have to figure out ways to move the plants up and down. You'll need to maintain the proper distance between plants and light as the plants grow. Standard bulbs will do an acceptable job, however, you can buy special fluorescent bulbs designed expressly for growing plants indoors. These bulbs will be a bit more expensive, but the results are obvious in terms of healthy seedlings. For lots of options for getting started see the Seed Starting Equipment section of Yardener’s Tool Shed.
The basement is an ideal location for setting up a fluorescent light for starting seedlings. The temperatures are usually more constant in a basement, keeping between 60°F and 75°F throughout the whole year. Most basements have water available, which makes caring for the seedlings convenient. Folks without basements might consider building a seedling bench that harmonizes comfortably with the other houseplants in the living room. You can buy very attractive plant stands that work great with seed starting. See Seed Starting Systems in Yardener’s Tool Shed.
The keys to successfully growing seedlings under lights are the duration of light and the distance the light sits from the top leaf of the plant. Have your lights on for 14 to 16 hours a day, every day. Anything less will not produce the best growth. Use an automatic timer to turn the lights on and off. When seedlings are just little sprouts, hang the lights no more than 3 inches above. As the plants get their first true leaves, move the lights up to about 4 inches above those leaves. You can set the lights at 6 inches when the seedlings are several inches tall so that the light shines evenly on all the plants, even those on the edge of the shelf.
Heat for Seedlings
There are on the market special heating pads for helping seedlings get a better start. Run by electricity, these pads are set under the seedling tray or container and set to produce a level of bottom heat that keeps the temperature of the seedling planting mix at the proper temperature for maximum success. We consider these devices optional for the beginner or someone starting just a few seedlings each year. For the serious gardener, starting lots of seedlings all year long, these devices are very valuable and worth the investment.
Prepare Potting Mix
Loosen and dampen the potting mix before you put it into your seed starting containers. It is easier to get a uniform level of moisture if you do it this way.
Dampen the mix to the consistency of a rung-out sponge. It should be wet, but not dripping, with no dry lumps.
Also, since new seedlings don't require fertilizer until they sprout their first true leaves, you don't really need a mix with fertilizer already in it.