What are the different methods and impacts of pruning tomato plants?
Side shoots, or “suckers,” are additional fruiting stems that emerge on tomato plants at the junctions of the main stems and leaf stems. Some folks recommend that gardeners prune tomato plants by removing all tomato suckers; I disagree. Contrary to what many think, suckers don’t sap energy from the main tomato plant, and allowing them to develop will not delay fruiting or ripening of any tomatoes from the main stem. Judicious removal of some suckers, however, will lead to more controlled growth and make supporting the plant easier, especially with an indeterminate variety.
Essentially, suckers are the tomato plant’s way of passing on its genetic heritage by producing as many seeds as possible: More branching leads to more flowers, which lead to more tomatoes, which lead to more seeds, which, to a plant, mean survival.
Removal of suckers could have implications for overall yields. Each sucker allowed to grow will provide additional flower clusters, and hence create additional chances for fruit set. Sometimes during the season, the majority of the flower clusters on a tomato plant’s main stem will open when the temperature or humidity isn’t suitable for pollination, which can result in blossom drop. If you’ve pruned tomato plants by removing all suckers, then the plant will bear only a handful of fruit, with no method available for the plant to produce additional flowers after the hot weather has passed. If suckers would’ve been maintained, the number of flower clusters would’ve increased, and flowers on those additional growing shoots likely would’ve opened later under more suitable conditions, thus increasing the yield of the plant.
Tomato suckers that are allowed to grow will also furnish additional foliage cover. In climates where searing sun regularly beats down on exposed, developing tomatoes, sunscald poses a definite concern. Because direct sun isn’t needed to promote ripening, the shade cover provided by the suckers’ foliage is beneficial.
Ideal management of suckers is somewhat dependent on the type of tomato. Determinate tomato varieties grow to a genetically predetermined height and width, and then produce flowers at the ends of their branches. In a sense, they are “self-pruning,” and any removal of suckers would reduce the potential yield of the plant. An indeterminate tomato plant, however, extends its main growing stem indefinitely and will generate suckers at each point of a leaf stem attachment. Indeterminate tomato plants can quickly grow out of control because the suckers themselves go on to produce suckers, so a plant can become dense and complex by midseason.
Skillful “topping” of fruiting tomato branches and stems at particular heights is a way of controlling growth. Because more flowers form than will pollinate and ripen before the end of the season, topping will also ensure that a plant doesn’t put energy into developing tomatoes that will never get a chance to ripen properly. Removing the top of the plant is also an excellent way to prevent plants from becoming so top-heavy that they topple in storms or develop kinks in their branches.
An easy way for gardeners with long seasons to extend the harvest even further and put removed suckers to good use is to cut and root some of the suckers. Suckers root easily and can be planted in early summer. They will yield tomatoes that are clones of those of the plants they were taken from.
To do this, cut a 6-inch-long sucker from one of your healthy plants and put it in a glass of water. After it has a nice set of new roots, pot it up in fresh potting mix and allow it to adjust in a shaded location for a few weeks before setting it into its final digs. Some gardeners have found that suckers will root directly in the garden if placed in a shaded area. Keeping the rooting suckers out of direct sun is important. Typically, a tomato sucker will root and begin to show renewed growth in a few weeks at most. Often, a sucker planted in damp soil will wilt just a bit until new roots begin to grow.
Adapted from Epic Tomatoes, Storey Publishing, 2014.
(Top) Photo by Stephen L. Garrett: Put tomato shoots to good use by growing them into more plants.
(Bottom) Photo by Stephen L. Garrett: Suckers left alone won’t sap life from tomato plants, so you don't have to remove them all.