Garden Variety: Prune tomato plants to maximize garden production

Tomatoes are a favorite in Kansas gardens, and gardeners are always looking for ways to get the earliest, largest and best-tasting fruit while fighting the weather and at least a dozen common pests. One beneficial practice with which some tomato gardeners may be unfamiliar is pruning. Although pruning is popular in ornamental gardens, it is rarely performed (or needed) in the vegetable/food garden. Tomatoes are one of the rare food garden plants that benefit from removal of some tissue through the season.

What is meant by pruning? Simply put, pruning is the selective removal of stems, branches, etc. with a specific purpose in mind. Pinching is another name that gardeners might use to describe the act of pruning, especially when pruning soft tissues that can be removed with the pinch of a hand.

Pruned tomato plants produce earlier and larger fruit than unpruned plants. Pruning also creates a less favorable environment for pests like Septoria leaf spot. The practice is an art, though, and gardeners must take care to find a balance, pruning enough to benefit the plant without adding extra stress.

Before you begin, find out if the plants are determinate or indeterminate varieties. Determinate tomato plants are more upright and uniform, but they stop growing once fruit sets on the top bud of the plant. Their fruit tends to ripen over a month or two. They are also sometimes described as “bush-type.” Roma, Celebrity, and Patio are common determinate varieties.

Indeterminate tomato plants are more vining and sprawling. They produce tomatoes all over the plant and for as long through the season as they are healthy enough to do so. Many cherry tomatoes are indeterminate as well as the varieties Jet Star, Brandywine and Cherokee Purple.

Some resources suggest leaving determinate plants to grow and only pruning indeterminate varieties. However, more evidence suggests that all tomatoes can benefit from some level of pruning. The most important thing is to keep pruning at a minimum, concentrating on removing tissue that can take energy away from fruit production and opening the center of the plant.

The most basic level of pruning involves removing suckers. Suckers are shoots that grow from the leaf axil — the point where the leaf stem meets the main stem of the plant. If you think of the tomato plant as a small tree and a leaf stem like a branch on that tree, the leaf axil would be where the branch meets the main trunk of the tree. The sucker grows out between the two.

To remove suckers, pinch them between two fingers until they pop loose from the plant. If the sucker fails to break cleanly away from the plant, use pruners or a knife to smooth torn tissue. If using tools, sterilize before moving on to the next plant.

Removing suckers on the lower portions of the plant is the most important. Experts generally recommend removing all suckers up to the fork where the first flower cluster grows on determinate varieties, and all suckers up the second flower cluster for indeterminate varieties.

Suckers should be pruned from tomato plants while they are still small and tender if possible. If suckers get too large, leave them on the plant as removal may cause undue stress.

Additional pruning may benefit some indeterminate varieties. Especially in cases where indeterminate varieties are staked, caged or trellised, gardeners may wish to prune or pinch out all the growing tips once the plants have reached the height of the stake, cage or trellis. This encourages the plant to produce lateral shoots and prevents the top from breaking over for lack of support. To perform this pruning, simply pinch and remove the tips as needed.

Again, while light pruning benefits plants, gardeners should focus on removing as little as possible. Overpruning of tomato plants may increase the amount of sunburn, cracking and blossom end rot on tomato fruit.

• Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.

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