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Tip of the Week: Tomato Maintenance

Follow these tips to ensure a great tomato harvest this summer. Included: the difference between determinate and indeterminate tomatoes, and what it means to you.

Follow these tips to ensure a great tomato harvest this summer.

Determinate tomato plants stop growing at a certain height, while indeterminate tomato plants keep growing over the whole season. Determinate varieties flower and set their fruit within a certain time frame. Indeterminates flower and fruit throughout the season.

What does this mean to you? If you plan to harvest and can your tomatoes, determinate plants may be the better choice. You can harvest them all at once and do a big batch of canning. If you'd rather eat your tomatoes fresh over a long period of time, indeterminate varieties make better sense. Determinate tomatoes should not be pruned. Indeterminates can be pruned.


Tomatoes are particularly sensitive to low nighttime temperatures. In spring or early summer, if night temps are below 55°F, tomatoes that have set flowers may drop them, resulting in fewer fruits. In later summer if the days are above 90°F but nights are below 76°F, the same thing may occur. In these scenarios you should protect your plants at night by placing a lightweight fabric cover over them. In cool climates, black plastic mulch can help keep the soil warm, which tomatoes appreciate.


Tomatoes require ample but careful watering. If the soil dries out, they may suffer blossom-end rot. If you water too much after the fruit has set, the tomato skins may split. In general, soak the soil six to eight inches deep twice a week. Mulch around the plants to help the soil retain moisture. Keep the area free of weeds so the plants won't have to compete with them for water.


Tomatoes are known as "heavy feeders"—plants that thrive on fertilizer. When choosing a fertilizer, do not choose one that is high in nitrogen—the first umber in a fertilizer formula such as 10-10-10—because this will produce lush foliage instead of flowers and fruit. Phosphorus, the second number, supports flower and fruit set.

Pruning and Supports

If you don't plan to support your tomato plants with stakes or cages, mulch around them with clean straw or black plastic so that if fruit contacts the ground, it won't rot. If you use supports, place the stakes or cages near/around the plants early in the season; placing them later might disturb the roots.

Plants grown with no support are usually not pruned but instead left to branch and grow naturally. They will sprawl across the ground. The fruit may become susceptible to slugs and certain diseases.

Plants grown with cages for support may be pruned to leave four or five main stems. As the plant grows, turn its stems into the cage. Plants the grow larger than the cage and droop down over the sides often still produce well. Alternatively you can add taller stakes to the cage and tie the stems to these.

Plants grown with stakes or on trellises are usually pruned so they have one or two main stems. Tie these to the stakes with soft twine or strips of fabric. As the plant grows taller, add more ties. Keep pruning over the season by removing all or nearly all branches that start to grow from the leaf axils (where the leaf stem meets the main stem). These branches are known as suckers. Tomato plants that are pruned produce fewer tomatoes, but the will be larger tomatoes. Reminder: Do not prune determinate varieties.

Pests & Diseases

For help with tomato pests and diseases, we recommend the Tomato Problem Solver web pages at Texas A&M.

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