As the seedlings grow, move the lights up, keeping them just a few inches above the tops of the plants. If you do use a sunny windowsill to grow your seedlings, rotate the plants every few days so they don’t have to reach for the light. Seedlings that are stringy looking, weak or pale are not getting enough light. There should be no more than an inch of stem between the surface of the soil and the first little leaf. I generally leave artificial lights on for 12 to 16 hours a day; I’ve also left them on 24 hours a day with equally good results. With warm conditions and enough light, seedlings will grow rapidly. Their first two oval leaves will soon be succeeded by sets of true leaves. At this point, its okay to let the top 1/2 inch of soil dry out between watering. Check soil moisture by putting your index finger into the soil – if its dry below your first joint, its time to water carefully with a gentle trickle from faucet or watering can.
Pricking out and potting up
. When seedlings are 2 to 3 inches tall and have several sets of true leaves, its time to move them to deeper containers or individual pots so they have room to grow. Fill the new containers with pre-moistened mix. With the help of a fork thrust to the bottom, lift the seedlings gently from your germinating container. Try to get all the roots and disturb them as little as possible. Make a planting hole in the new container and nestle the seedling into its new home a little deeper than it was originally. If your tomato plants are spindly with long stems, you can actually bury the stems right up to the topmost cluster of leaves and new roots will grow along the buried stems.
Gently press the mix around the transplanted seedlings and water them gently to settle the soil. Now is the time to begin feeding your plants once a week because starting mixes contain little if any plant food and the seedlings will have used up the entire stored food source available in its mother seed. Use a good liquid fertilizer or fish emulsion diluted to half normal recommended strength. Continue to give your rapidly growing seedlings as much light as possible and rotate them regularly so they grow evenly and don’t lean in one direction.
Planting seedlings in the garden
. In 3 or 4 weeks, or when the weather outdoors has warmed into the 50 degree range at night, its time to harden off or gradually acclimate your seedlings to outdoor conditions. Put them outside in a protected shady spot for a half day at first, then 2 or 3 full days, then gradually move them into full sun, starting with mornings then all day long. Plan to transplant into the garden in the late afternoon or on a hazy or cloudy day to minimize stress. Firm the soil around the plants and water well. Keep your young plants moist but not soggy. Mulch them with a good thick layer of compost, well-aged manure, straw or other organic material. This will provide the even moisture balance needed for healthy, disease-free growth and early big fruit sets, and will also discourage weeds.