How to Prune Tomato Plants

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Vine-ripened tomatoes are a summer treat. But should you prune your tomato plants? Read on to learn when it's best and how to do it.

For home gardeners who like to grow fruit and vegetables, few things herald the arrival of summer quite like vine-fresh tomatoes. (OK, maybe strawberries. But you know what we mean.)

Tomatoes are rich in vitamins and cancer-fighting antioxidants. Homegrown tomatoes are even healthier than those from the store because they can be grown without pesticides or chemical-loaded fertilizers. Plus, they taste a lot better!

When allowed to ripen in the sun and picked just before eating, homegrown tomatoes have a completely different flavor than the mass-produced ones that ripen in warehouses. (If you can get your hands on some heirloom tomato seeds, even better.)

Tomatoes don’t require pruning to grow and bear fruit, but some gardeners prefer to prune. We checked in with the experts at the National Garden Bureau (NGB) for tips on how and when to prune tomato plants.

tomato vineCosmin Sava/Shutterstock

Why Prune Tomato Plants?

NGB says pruning tomatoes creates an optimal balance of vegetative growth and fruit production. Pruning can result in larger fruit and an earlier harvest. It reduces the amount of foliage and allows more light and air to reach the fruit. Less foliage also increases light penetration and air circulation in the lower canopy, which the NGB says reduces disease susceptibility and severity.

Note that tomatoes are determinate or indeterminate, and that determines (sorry, we couldn’t resist) whether you need to prune.

Determinate Varieties

Determinate varieties such as grape and Roma, are smaller plants with smaller fruit. They produce a lot of fruit over a short period of time, but only once in the season. They do not need to be pruned. (The NGB says some gardeners find that pruning determinates makes the plants easier to work with and produces larger fruit, but that is an individual choice.)

Indeterminate Varieties

Indeterminate varieties include beefsteak, cherry and heirloom tomatoes. These plants grow much larger than determinate varieties and produce fruit all season. They typically need to be staked or strung. And they need to be pruned.

When to Prune Tomatoes

Per the NGB, pruning of indeterminate tomatoes is typically done four to five weeks after transplanting, which means late spring for most growers.

If you started with plants instead of seeds, wait until the plants are one to two feet tall before pruning. NGB also recommends pruning prior to stringing or staking the plants, as this simplifies the process of accessing and removing suckers (the new shoots that pop up at the junction of a stem and branch).

Remove suckers when they’re two to four inches long, the NGB says. Once they grow larger than that, pruning might result in large wounds that are slow to heal, stressing the plant and exposing sites for infection.

It’s also best to prune on a dry day, about mid-morning after the dew on the plants has evaporated. Then the plant has the rest of the day to soak up the sunshine and recover.

Tools Needed to Prune Tomatoes

You don’t need a lot of equipment to prune tomato plants. The most basic tool is a good pair of pruning shears, sharp ones. While most pruners will do the trick, a pair of bypass pruners are ideal. These steel shears from Fiskars are a solid set for less than $15. For an upgrade pick, the F2 from Felco is the gold standard in the industry.

A set of tomato stakes or even a wire cage for the remaining vine to grow on is good to have handy as well. You’ll also want a disinfectant to spray on the plants where you’ve made a cut. There are a number of household materials you can use for that, just make sure to check that it’s safe for plants. It helps prevent disease.

How to Prune Tomatoes

It’s a pretty simple process, but you don’t want to start pruning tomatoes until their 1-2 feet tall to help prevent a shock to the plant.

  1. First, find the suckers that you’re going to trim from the plant.
  2. From there, prune your tomato plants to create one, two or three main branches by removing of all but one or two suckers.
  3. Train the remaining vines to grow on stakes, strings or a cage structure. As the vines continue to grow, prune additional suckers that pop up. This is especially important as vines get bigger and heavier with tomatoes growing on them.
  4. Prune your plants early in the day, before it gets hot outside. That helps the plant heal.

The NGB notes that if your tomatoes are potted versus in-ground, there’s little difference in pruning methodology. Determinate plants probably won’t need to be pruned, and indeterminate plants can be pruned per the guidelines offered above.

Tomato Pruning Tips

  • Smaller suckers can be easily removed by pinching them with your fingers, using a sideways, snapping motion.
  • Larger suckers should be removed with a sharp knife or clean pruning shears to prevent tearing the plant’s tissues.
  • As the season goes on, remove all leafy suckers beneath the first fruit cluster. This prevents disease from splashing up on the lower leaves.
  • Later in the season, it’s a good idea to prune or “top” the growing tip of each main stem about four weeks before the first frost. This way the plant puts its energy into ripening all remaining fruit rather than producing new fruit.