4. Keep the lights bright.
Check your trays daily. As soon as you see sprouts, remove the plastic covers and immediately pop the trays beneath lights. You can invest in grow lights (which provide both “warm” and “cool” light), but many gardeners have good results with standard 4-foot-long fluorescent shop lights. Set your seedlings as close to the light as possible—2 or 3 inches away is about right. When seedlings don’t get enough light, they grow long, weak stems. As the seedlings grow, raise the lights to maintain the proper distance.
And don’t worry about turning off the lights at night. Contrary to popular belief, seedlings don’t require a period of darkness. Fluorescent lights are only one-tenth as bright as sunlight, so your seedlings will actually grow better if you leave them on continuously.
5. Feed and water.
Your seedlings will need a steady supply of water, but the soil shouldn’t be constantly wet. The best method is to keep the containers inside a tray, water from the bottom, and allow the soil inside the containers to “wick up” the water.
If your growing medium contains only vermiculite and peat (as many seed-starting mixes do), you’ll also need to feed your seedlings. When the seedlings get their first “true” leaves (not the tiny ones that first appear, but the two that follow), mix up a fish emulsion solution one-quarter to one-half the recommended strength and add it to the seedlings’ water every other week. As the plants grow bigger, gradually increase the strength of the mixture.
6. Keep the air moving.
Your seedlings need to be big and strong by the time you move them from their cushy indoor surroundings to the harsh realities of the outside world. You can help them grow sturdy, stocky stems with a small fan. As soon as you see those first true leaves, set the fan to blow lightly but steadily on the seedlings, all day long. The air circulation also will minimize their chance of fungal disease while they’re crowded together indoors.