Choosing healthy, robust tomato seedlings form the nursery is a big step toward raising vigorous plants brimming with fresh fruit, but it is only the first step. Before you consider transplanting them to the garden, get a soil test done to determine the needs of your specific soil. Follow the recommendations for amending the soil to balance nutrients, improve texture and drainage, and adjust the pH to between 6.2 and 6.8.
Prepare seedlings for transplanting by hardening them off. Hardening off is the process of slowly acclimating the tomato plants to outside conditions. Begin by placing the plants outside in sheltered location during the day and bringing them inside at night; along the side of a building or a fence is ideal. Gradually increase exposure to both sun and wind over the next week.
Dig a hole 18 inches in diameter and 8 inches deep. Add a quart of well-rotted manure to the hole and mix in well with the existing soil. Pour 2 to 3 gallons of water in the hole to saturate the soil at the bottom of the hole. Water should drain slowly into the surrounding soil.
Remove the tomato plant from the plant cell and lay the plant down in the hole. Gently bend the stem to bring the tip of the plant upward so the top of the plant is 4 to 5 inches above the soil line. Use care not to snap the stem. Roots form along the stem, creating a vigorous root system to support the growing plant. Fill in around the stem with soil and firm down gently to remove air pockets and secure the plant.
Water thoroughly to saturate the soil to the root level. Keep the soil moist until new growth appears on the seedlings. Water deeply once a week and apply water-soluble fertilizer designed for tomatoes on a 10- to 14-day schedule throughout the summer.