Plant tomato transplants in the garden after the last average frost date in your area. Although seeds can be directly sown in the garden and plants grown to maturity in warm areas, most gardeners buy transplants or start seeds indoors six to eight weeks before their average last frost date.
Plant small bush varieties 24 inches apart and larger varieties, especially sprawling indeterminate plants, 36-48 inches apart in rows 36 inches apart.
Tomato transplants should be planted deeper than other vegetables. While most plants are transplanted so the top of the soil in their container is level with surrounding garden soil, tomatoes, and their relatives tomatillos, are unique. They can form roots along their stems. The extra roots help anchor the plant and provide more opportunity for water and nutrient uptake, which is especially helpful when starting with tall, leggy transplants.
Prune off the transplant's bottom leaves and set the root ball in a planting hole deep enough so that only the top cluster of leaves is showing above ground. If the transplant is exceptionally tall, take a trowel and dig a 4- to 6-inch deep trench in the soil. Lay the plant horizontally in the trench and turn the uppermost portion of the stem vertically so the top cluster of leaves pokes out of the soil.
After planting, stake or cage all tomatoes with the exception of small bush or patio varieties, which can often support themselves. Waiting a few weeks after planting to install stakes or cages can injure the plant's roots. Cages and stakes keep tomatoes off the ground, helping to prevent fruit rot and numerous diseases.
Tomato cages are typically made of heavy-gauge wire and stand 5-6 feet tall. Firmly anchor the cages to the ground with stakes to keep the plants from blowing over and uprooting themselves during storms. They should have openings wide enough for your hand to reach inside to harvest.
Stakes are another way to help tomatoes stand tall. They need to be at least 8 feet high and 1 inch wide. Pound the stake at least 12 inches into the ground and 4 inches from the plant. Attach the stem to the stake with garden twine, self-adhesive fabric, or strips of cloth.
If desired, fertilize plants monthly with a balanced plant food such as 5-5-5 when the first tomatoes are about the size of golf balls.
After the soil has warmed, mulch plants with a 2- to 3-inch-thick layer of organic mulch, such as straw or finely shredded wood chips, to prevent weeds and to maintain soil moisture. Mulch is also valuable for preventing soil and soilborne diseases from splashing onto leaves when it rains. At the end of the season, enrich the soil by tilling in the mulch. It will decompose and add valuable nutrients for next season.
Tomatoes grow best when they have consistent moisture. If it rains less than 1 inch per week, supplement by watering. To prevent diseases, avoid wetting the foliage. Use a watering can or wand to deliver water directly to the root zones, or use a drip irrigation system.
Pick fruits when they are firm, full size, and fully colored. Tomatoes mature and ripen best at temperatures close to 75 degrees F. When the temperature rises about 90 degrees, the fruits soften and develop poor color. Tomatoes will ripen when picked at their green mature size.
Before a hard frost, harvest all but the greenest fruits and bring them indoors to a 60- to 65-degree F room, and wrap them individually in a sheet of newspaper. Check the fruits once a week for ripeness and remove any tomatoes that are decayed or not showing signs of ripening. Also, whole plants can be uprooted and hung in a warm, sheltered location, where the fruits can continue to ripen.
Once picked, ripe fruits can be stored for up to two weeks at 55 degrees F. They can also be stored in the refrigerator but will not taste as good as those stored at cool room temperature.