Tomato suckers or side shoots are the growths that appear in the junction between the stem and a branch of a tomato plant. 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.
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.
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 all at once. 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.
As long as you have a strong main stem, it’s fine to leave a few suckers on the plant. The general consensus is to leave two or three suckers to improve yield, but not to let every sucker grow.
Some gardeners like to prune out everything below the first flower cluster to develop a strong central stem. Others prefer to leave a couple of suckers on the lower portion of the plant because these can be easily supported by staking. Then they prune the suckers from the remaining top growth of the plant to prevent it from becoming too top-heavy and falling or splitting.
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.