Tomato suckers and pruning tomatoes

Most of us have our tomato plants in the ground by now and are anxiously awaiting that very first ripe tomato. For now, however, there is a particular issue which needs to be addressed. This issue is pruning-shaping the plant so that it will grow and produce the number and size fruit which we desire. This article is my annual advice regarding this important topic.

Tomatoes are generally classified as either determinate or indeterminate. Determinate tomato plants have a genetically predetermined number of stems, leaves, and flowers (and thus fruit). Their growth follows a pattern of vigorous vegetative growth followed by a flush of flowers and fruit, after which there is a period of final leaf expansion and an end to further vegetative growth. Commercial growers like this type of tomato because most of the fruit can be harvested all at once. A few examples of popular garden determinate varieties are Amelia, Roma, Better Bush, Celebrity, Carolina Gold, Rutgers, and Marglobe. Most commercial varieties are determinate. Determinate varieties grow shorter and produce fewer fruit than their indeterminate counterparts.

Indeterminate tomato plants continue to grow and produce leaves, stems, and fruit throughout the season as long as growing conditions are favorable. Popular indeterminate varieties include Beefsteak, Beefmaster, Better Boy, Big Beef, Big Boy, Park’s Whopper, Goliath, Super Sweet 100, and many others. Indeterminates can have one main stem or several stems, depending on how they are pruned. The fewer the number of stems, the larger but fewer the fruits will be. 

Tomato pruning involves retaining or removing parts of the tomato plant known as suckers. Suckers are side shoots which appear in the axils, or crotches, between the leaf petioles and the main stem. If allowed to remain, suckers will grow to be just like the main stem-that is, complete with flowers, fruit, and additional suckers.

Why are tomato suckers often removed? Pruning is done because, if not removed, the suckers compete with the main stem and its fruit for nutrients. While it is true that more fruit will result from leaving the suckers to grow, the resulting fruit will be somewhat smaller and the plant will become more cumbersome and thus harder to support. Pruning, therefore, is much like trimming a shrub in order to control its size and shape. 

Pruning also affects the health of the tomato plant. Pruned plants, with more leaves being exposed to the sun, tend to dry faster after rains and stay drier, so harmful bacteria and fungi have less opportunity to spread and cause disease problems. A more compact and well-trained plant, directed upward rather than outward, will tend to have fewer problems with leaf spots and fruit rots because its leaves stay drier and free of soil residue, which often harbors disease-causing organisms, resulting in blights.

On the other hand, not pruning suckers will cause the tomato plant to develop more leaf cover and thus more shade for ripening fruit, which can minimize sunburn and scalding. This can be a distinct advantage for varieties that naturally form less leaf cover and thus are more vulnerable to the rays of the harsh afternoon sun. 

Is pruning necessary? No. Pruning suckers is not a requirement and many gardeners do not even bother with it at all. However, if you are one of those who do, you will appreciate knowing that whether or not to do so depends on the type of tomato you are growing. 

Determinate tomatoes need no pruning other than the removal of all suckers below the first set of flowers. Additional pruning will not affect fruit size or plant vigor. However, if pruning is done anywhere above the first flower cluster, the tomato harvest will be reduced. 

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 may become top heavy and out of control if not well supported. On the other hand, removing all the suckers will result in a more compact and manageable plant but, as previously stated, it will also lessen your tomato yield. 

As long as your tomatoes have strong main stems, it’s fine to leave a few suckers on the plant. The general recommendation is to leave two or three suckers to improve yield, but not to let every sucker grow. 

If you are concerned about your indeterminate tomato growing tall and cumbersome, you might try this: once the plant has reached an ideal height (such as the top of your support cage or stake), simply pinch out the main terminal (top) bud on each main branch. This will help keep the plant at that height. Of course, your harvest will be reduced accordingly. 

Tomato pruning is more trial and error than precision, so look at it as an experiment. When you first start pruning, do less rather than more. If you grow the same varieties year after year, you’ll get a feel for how they respond to pruning. 

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, and former Perry High School horticulture instructor. He can be reached at (478)954-1507 or timlewis1@windstream.net.