Seedlings need more intense light than full-grown plants. If they don’t get 14 to 16 hours of strong light a day, most become spindly and weak. Although many gardeners start their seeds on windowsills, the light from a window during the short days of winter often isn’t enough to grow strong, sturdy seedlings.
A grow-light system will provide seedlings started indoors with enough light to produce healthy, compact transplants for the garden. Here’s how to get the most from your lights:
Shopping for a Seed-Starting Mix
When shopping for a seed-starting mix, be sure the product is specifically labeled for seed starting and not as “potting soil.” Good-quality mixes contain some vermiculite, a form of the mineral mica, to promote drainage. Recently, it has been discovered that vermiculite can contain trace amounts of asbestos, a mineral that can cause lung disease. The EPA recommends working with this material in a well-ventilated area (preferably outdoors) and dampening the mix as soon as you open it to keep any particles from becoming airborne.
When you’re ready to transfer seedlings to larger pots, you can use potting soil. Look for products that contain composted fir or pine bark (don’t settle for plain “bark” or “processed bark”). Research has shown that properly made bark compost helps prevent diseases, such as damping-off, a fungal disease that can quickly kill newly sprouted seedlings.
Most seedlings will do better if you grow them beneath fluorescent lights. You can buy expensive grow lights, but the 4-foot-long shop lights sold at hardware stores work just as well and cost much less. Start with new tubes—fluorescent tubes become dimmer over time. Don’t bother with incandescent bulbs. Their light does not stimulate growth well.
Suspend your light fixture from the ceiling over a table or bench. To protect the table or bench from water, cover it with a plastic sheet.
Heating Mats and Cables
Most seeds—including tomatoes and peppers—germinate much faster in warm soil (about 70° to 75°F). To provide those toasty temps, heating mats and cables come in handy. You just plug them in and set your containers on top of them.
Some of these devices connect to a control unit that allows you to set the temperature at the exact level needed for germination. Others have thermostats, switching on and off automatically to keep the soil temperature in the mid 70s or so.
Keep in mind that most sprouted seedlings grow better in slightly cooler temps (upper 50s to lower 60s), so remove the heating mat or cables after the seeds have sprouted.
For peat pots, paper pots, and soil blocks, a capillary mat can be a big help. Capillary mats allow the seed-starting medium to draw water from a reservoir as needed, so you don’t have to monitor moisture levels as often. Simply set your containers on top of the mat and keep the reservoir filled (usually one filling every 4 or 5 days is all that’s needed). The mats are made of a fiber that “wicks” water, spreading the moisture evenly from the reservoir to all corners of the mat. You can even put liquid fertilizer in the reservoir to feed larger seedlings. One drawback is that, as the seedlings grow, their roots may attach to the mat; if that happens, just peel off the mat at transplant time.
Seedlings growing in a soil-free or lean potting mix will need small doses of plant food, starting at the time the first true leaves develop. For the first 3 weeks, water them once a week with a half-strength solution of fish or seaweed fertilizer, compost tea, or one of the liquid organic fertilizers specially formulated for seedlings. After that, feed the seedlings with a normal-strength solution every 10 to 14 days. If you’re growing your seedlings in a potting mix that contains compost or other nutrients, you may not need to feed them as often.