Tomato Plants Can Be Pruned or Not, Your Choice

Q. You mentioned it is possible to cut back tomatoes for a fall harvest in hot climates. How far back do you trim them?

A. No cutting back of tomato is necessary but sometimes it can help invigorate a plant which has become too large and stimulate more production. Tomato is a perennial plant that can continue to grow larger and larger if there are no freezing temperatures.

Tomato sucker coming from a larger stem

            Tomatoes are annuals in temperate climates that have freezing weather because of the killing low temperatures. However, cutting or trimming back tomatoes to side shoots can control the size of the plant, keep it more compact, and encourage new growth that will flower and produce fruit.

Tomato smaller size after summer pruning

            The two key questions are when to cut them back and how. Cut them back at a time when new growth is produced during cooler temperatures that allow for fruit to set from the flowers. The magic temperature that allows fruit to set is between 90 and 95F and lower. 

Tomato fruits with sunburn because of intense sunlight after pruning

            These temperatures appear in the Fall, usually toward mid to late September. Therefore, cutting them back around the end of August to the first week in September should provide some new growth over 2 to 3 weeks as temperatures cool.

            Timing is always a bit of a gamble because we don't know what the temperatures will be. We can only predict them from historical fall temperatures and experience.

Summer pruning tomato for size control

            How to cut them back is more difficult to explain. It might be easier to tell you what you shouldn't do. Don't cut tomatoes back to a single stem with no side growth immediately below the cut.

            Reduce the size by cutting 1/4 inch above side growth. New growth will come from leaf axles, i.e. where a side shoot is attached to a main stem.

Tomato growing new side shoots or suckers lower on the stem after pruning

            When you are finished cutting back a tomato plant it should look like a smaller version of the original plant with lots of side shoots still remaining. If you cut back a plant dramatically you may need to throw some shade cloth or a light colored and lightweight breathable fabric to provide to some shade and prevent sunburn to the main stems.

            After cutting back a plant, lightly fertilize the soil or give it a liquid fertilizer applied to the leaves. Liquid fertilizers applied to the leaves should be done early in the morning or late in the day this time of year. It would be ideal to apply a surface mulch to the top of the soil such as straw, animal bedding, shredded newspaper or grass clippings to preserve soil moisture.