Select several varieties that mature at different times to extend your harvest.
If you don't purchase plants, start seeds indoors in flats or pots 6 to 7 weeks before the average last frost date, and set out transplants when the soil is warm and all danger of frost is past.
Select a site in full sun (except in very hot climates, where some shading will be desirable to prevent blossom drop).
A week or so before planting, fertilize with 1 to 1 3/4 pounds of 5-10-10 or its equivalent per 100 square feet. Increase the amounts for sandy soils.
Set up trellises, cages, or stakes at planting time.
Dig planting holes 18 to 24 inches apart if you plan to stake or trellis the crops, 36 to 48 inches apart if the plants aren't trained.
Mix a teaspoon of 5-10-10 fertilizer or its equivalent and 1 tablespoon ground limestone with soil at the bottom of the planting hole (except in high pH soils). Pinch off two or three of the lower branches on the transplant and set the root ball of the plant well into the hole until the remaining lowest leaves are just above the soil surface.
Water generously and keep the plants well watered for a few days.
Provide an even supply of water all season.
If staking or trellising, prune suckers to allow one or two central stems to grow on staked plants, two or three central stems for trellis systems.
Apply a thick layer of organic mulch 4 or 5 weeks after transplanting.
Side-dress tomato plants initially when the first clusters of fruit have formed and every 3 weeks thereafter. Two cupfuls of 5-10-10 or its equivalent are generally adequate for 20 plants.
See our article Summer's Bad Guys by Charlie Nardozzi for controls of common tomato insect pests such as tomato hornworms and whiteflies. See our article Tomato Diseases by Carolyn Male for controls of common tomato diseases such as early blight and verticillium wilt.
For best flavor, harvest tomatoes when firm and fully colored. Fruits will continue to ripened if picked half ripe and brought indoors.