Tomato suckers or side shoots are the growths that appear in the junction between the stem and a branch of a tomato plant call the "axil". When left to grow, tomato plant suckers will become another main stem with branches, flowers, fruit, and even more suckers of their own.
Why Pruning Is Recommended
Pruning tomato suckers is often recommended because the resulting new stem is competing for nutrients with the original plant. Your plant may have more fruit if you let the suckers grow, but the tomatoes will be smaller and the plant will be more cumbersome, requiring a lot of effort to stake as the summer progresses. Pruning tomato suckers makes your plants more manageable and more robust at the same time. Pruning indeterminate tomato plants improves air flow and helps reduce disease, as leaves dry faster after rain, making them less susceptible to diseases that thrive in prolonged moisture. Pruning also makes it easier to spot pests that are easily camouflaged in a thick canopy of leaves. Pruning also speeds fruit ripening.
Types of Tomatoes That Need Pruning
Pruning tomato suckers is not a must and many gardeners don’t bother with tomato pruning at all. Some varieties of tomatoes do better when pruned, while it matters less with others.
Tomatoes are categorized as either determinate or indeterminate, depending on their growth habit. Since indeterminate tomato plants can get extremely large and will keep producing tomatoes all season, they can handle some pruning. If you leave all the suckers to grow, your plants will become heavy and out-of-control. Keep in mind, though, that if you remove all of the suckers, the plant will be more compact and yield fewer tomatoes throughout the season, but they'll typically be bigger fruits. Pruning indeterminate tomatoes also allows more space for extra plants in the garden.
In contrast, determinate varieties of tomatoes don’t require any pruning at all. These tomato plants are naturally more compact; they're genetically programmed to reach a certain height and stop growing. They don’t usually set their fruit until the branches are fully grown, and then they set their fruit within a pretty short window. Since no new fruit will develop after pruning, nothing is gained by trimming off the tomato suckers on these types of plants.
How and When to Prune Tomato Suckers
The earlier you prune the tomato suckers, the easier it is. Small leaves and two-to-four-inch stems can be snapped off with your bare hands. Stems thicker than a pencil should be cut out with sharp pruning shears to avoid damaging the plant. Make sure to clean your pruners with an alcohol wipe between plants to avoid spreading any disease among plants.
As long as you have a strong main stem, it’s fine to leave a few suckers on the plant.
Pruning can take place throughout the growing season. At planting time, remove the lower leaves and bury the stem deeply in the soil. Roots will grow along the stem, helping to add stability to the plant.
As the plant grows throughout the season, remove leafy suckers beneath the first fruit cluster so they won't slow the development of the fruit. Pruning leaves near the base of the plant also helps prevent soil-borne diseases that can splash onto leaves. Be careful not to over-prune--some leaves are needed to protect the fruit from sunscald, particularly in the hot south.
Pruning late in the season is a race to ripen fruit before the first frost. About 4 weeks prior to your area's expected first frost, remove the growing tip of each main stem. Called "topping," this pruning causes plants to stop flowering and directs all sugars into fruits to speed ripening.
Tomato pruning is more trial and error than precision, so look at it as a learning experience. When you first start pruning, do less rather than more. If you grow the same varieties year after year, you’ll get a good feel for how they respond to pruning.
Pruning Tomato Suckers. University of New Hampshire Extension