Tomato suckers are extra branches that grow from the leaf nodes on the main stem of a tomato plant. Suckers steal nutrients and energy from the plant. Some gardeners remove all suckers from their tomatoes, and some leave two or three and allow them to develop into fruiting branches. Indeterminate tomatoes are the types that produce suckers that must be removed. These are the types of tomatoes that must be staked or trellised.
Determinate tomatoes have a more bushy habit; they have only a certain number of blooms and fruits each season, and should not be pruned. If you remove branches from determinate tomatoes, you will be removing potential fruits, and the plants will not grow replacements.
Locate and Remove Tomato Suckers
Examine the main stem of each indeterminate tomato plant, and find the lower leaf nodes. These are the points where the leaf stems are joined to the main stem. When your tomato plants are about 18 inches tall, remove the lower two or three leaves entirely at the nodes. This causes the main stem to grow larger and stronger, making it capable of better water and nutrient transport.
Find the first blossoming branch. If you want to allow side branches to fruit, allow the suckers on the two leaf nodes above the first set of blossoms to grow as side branches. The lower on the plant the branches are, the more sugars they will produce. It also shortens the length that the main stem has to carry water and nutrients to supply the branch.
Allowing side branches to grow will give you more fruit, but they will be slightly smaller than if you remove all suckers. For the largest tomatoes, remove all suckers on indeterminate plants. For more, but medium-sized, fruits, allow controlled side branches to grow from a couple of selected suckers.
Locate suckers on the leaf nodes above the two you have selected to keep, and remove them. Pinch them out, or snip them if necessary to get a clean break. As the main stem continues to grow, suckers will develop at each leaf node all the way up the stem. Remove them as they appear. The larger you let suckers grow before removing them, the more energy they take from the fruiting portions of your plant.
Select only lower suckers as side branches. The farther up the main stem the suckers are, the weaker they are, because they produce less sugar.