How to Care for Tomato Plants

The tomato (Solanum lycopersicum) is a summer vegetable in the nightshade family. All tomatoes fall into one of two categories: determinate or indeterminate. Determinate tomatoes only grow to a certain size and produce a certain number of fruits, depending on the variety. Indeterminate tomatoes continue to grow vines and produce fruit for as long as conditions are favorable. Regardless of the difference in growth patterns, all tomatoes must be fertilized and are susceptible to the same pests, disease and frost damage.

Man picking tomatoes from plant in garden
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Add a tablespoon of Epsom salts to each tomato plant once a month to prevent blossom end rot.

Tomato Characteristics

Tomatoes come in many shapes, sizes and colors. Tomato sizes are characterized by weight and fall into three categories: beefsteak, cherry and grape. Beefsteak tomatoes can grow quite large at over 16 ounces, while small grape tomatoes mature to as little as 2 ounces. Some tomatoes are perfectly round while others, like roma varieties, are long and narrow, similar to a pepper. Oxheart varieties are heart-shaped with a pointed blossom end. Tomato colors include a wide range from white to black. Red and pink are the most common options, but purple and black varieties have gained popularity, particularly in specialty markets. Other colors include yellow, orange, green and various colors of stripes.

All tomato plants have green leaves and stems. Some small determinate patio varieties reach a maximum of 1- to 2-feet tall, while some indeterminate varieties can grow vines over 12-feet long in one growing season. Always read the plant description carefully before making a decision on variety.

Watch for Spring Frosts

Frost will kill a tomato plant, so have a plan in place in case there is a chance of a late spring frost after seedlings have been planted. Cut the bottom off milk jugs to create a mini-greenhouse to provide frost protection on a chilly late-spring night.

Because tomatoes are generally grown as annuals throughout the U.S. -- though they can be grown as tender perennials in -- all fruits should be harvested before the first expected frost in the fall.

Fertilization and Water Needs

Tomatoes are heavy feeders. After transplanting young seedlings, apply 1 tablespoon of 10-10-10 granular fertilizer per plant. With a rake, work it into the top few inches of soil in a circle all the way around the plant, out to 1 foot from the stem. Do not go deep enough to damage plant roots.

When the first tomatoes have reached the size of golf-balls, or reach half their mature size for smaller varieties, add 1 tablespoon of 10-10-10 fertilizer per plant again. Reapply fertilizer three weeks later, and again after another three weeks.

Always water thoroughly after fertilizing and make sure fertilizer does not touch leaves or stems. Do not apply fertilizer to plants that are stressed due to drought or heat.

Water plants any time the soil is dry 1-inch below the soil surface. Infrequent, thorough watering is better than frequent light watering because this allows water to reach plant roots more effectively.

Support and Pruning

Small, determinate tomato varieties can be sufficiently supported by tying the main stem to a stake or using a standard three-ring tomato cage. Larger indeterminate varieties require more significant support. Make a sturdy, long-lasting tomato cage out of concrete remesh, available in sheets from many home improvement stores.

Determinate varieties should not be pruned unless they have damaged branches, which should be removed 1/4-inch from the main stem with sharp, sterilized pruning shears -- sterilize tools with an alcohol wipe between cuts to prevent the spread of disease. Indeterminate varieties benefit from some pruning, especially if they outgrow their supports. Remove overgrown branches as needed to prevent broken stems due to fruit that is too heavy to support.

Managing Pests

Aphids are tiny white or green insects that cover leaves, stems and blooms. Knock aphids off of tomato plants with a shot of water from a hose. If a severe infestation occurs, spray ready-to-use insecticidal soap once per day as needed, thoroughly covering all leaves and stems.

Hornworms are thick caterpillars that grow to about 4 inches long. These pests can eat all the leaves off tomato plants overnight. Remove hornworms by picking them off plants as soon as they are seen. For a severe infestation of hornworms, apply a solution of Bacillis thuringiensis to the leaves of tomato plants in the evening; mix about 1 tablespoon Bt per gallon of water, but always follow your brand's label instructions. Reapply each night as long as hornworms are present. Store Bt out of reach of children and pets.

Banishing Blight

Tomatoes are not particularly prone to disease, but yellow and brown leaves close to the ground may indicate blight. The only way to control blight is to remove damaged leaves as soon as they are visible. Burn leaves or put them in the garbage. Never compost diseased leaves. To prevent blight, select a blight-resistant variety and practice crop rotation by planting tomatoes in a different spot each year.