Select a spot to plant your tomato plants that receives full sun. Plant tomato seedlings when daytime temperatures are above 65 degrees F and nighttime temperatures do not fall below 50 degrees F.
Prepare your garden soil 4 to 6 weeks before planting tomatoes plants. Spread 3 to 4 inches of compost on the soil. Use your shovel or a garden fork to mix the compost into the top 6 inches of soil.
Use a soil pH test to test your garden soil. Do this after mixing in the compost, as compost can change your soil's pH. Ideal soil pH for tomatoes is between 6.5 and 7.0. If necessary, you can adjust the pH by adding lime (calcium carbonate) if your soil is too acid or adding sulfur (calcium sulfate or iron sulfate) if it's too alkaline.
Select tomato seedlings that are 8 to 10 inches tall. Healthy tomato seedlings are dark green, with stems slightly larger in diameter than a #2 pencil.
Remove all leaves and stems below the top grouping of leaves.
Use one of two methods for planting your tomato seedlings. In early to mid spring plant your seedlings in trenches. Dig a trench that is 4 to 5 inches deep and long enough to encompass the stem of the tomato but short enough to place the top set of leaves 3 to 4 inches above the soil's surface. Alternatively, in late spring or early summer plant your seedlings in holes. Dig a hole that is deep enough to place the top set of leaves 2 to 3 inches above the soil's surface.
Mix 1 cup of commercial or organic 15-30-15 liquid fertilizer in 1 gallon of water. Add 2 tbsp. of the mix to the roots of each tomato plant before backfilling the hole or trench with soil.
Mulch your tomato plants with black plastic or an organic mulch. Use 2 to 3 inches of organic mulch around each plant. Mulch stabilizes the soil's temperature, retains moisture and reduces weeding.
Prune off flower clusters from tomato seedlings less than 12 inches tall. After the tomato plant has reached 12 inches, allow it to produce flower clusters. Once the tomato plant is tall enough to produce flower clusters, prune off all leaves and stems below the lowest flower cluster.
Use tomato supports like cages, stakes or a trellis system to keep foliage and fruit off the ground. Supported tomato plants have fewer problems with disease and insect pests.
Fertilize your tomato plants when the fruit is one-third of its full size with a balanced 10-10-10 organic or commercial fertilizer. Apply according to package directions. Fertilize your tomato plants again with the 10-10-10 fertilizer two weeks after the first fruits ripen. Fertilize again with the 10-10-10 fertilizer four weeks after the second application of fertilizer. Work each application into the top 2 to 3 inches of soil around the base of the tomato plant.
Water your tomato plants regularly. Give actively growing tomato plants 2 quarts of water a day. Increase the water to 3 to 4 quarts a day for tomato plants that are setting and ripening fruit.
Promptly pick ripe tomatoes. If you allow tomatoes to stay on the plant too long, they will begin to rot and attract insect pests. Pick up fallen tomatoes around the base of the plant.
Prune off yellowing, discolored or dead leaves and stems as soon as you see them. This prevents disease (bacterial and fungal) and insect pests from gaining a foothold on your tomato plant.