Grow Your Best Series: Tomato Pruning

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A common topic among vegetable gardeners is that of vegetable pruning. Should we prune tomatoes? Does it improve yield? Are there other benefits? Is it worth the time?

I used to be an anti-pruner. I had not seen any research to demonstrate yield benefits. And it’s true, the verdict is still out on pruning’s effect on yield. However, in situations where plants may be nutrient-limited or suffering from disease, pruning can reduce the number of fruit but often times improve the “marketable” or “desirable” yield. The fruit may be larger and may have less disease from a pruned plant versus un-pruned. Perhaps the primary reason I now choose to prune is to increase air flow in the plant canopy and remove diseased leaves to prevent its spread.

Through pruning tomatoes, you remove both suckers and leaves that are no longer serving the plants. Lower leaves on the plants are a source of nutrition through which nutrients are pulled into the rest of the plant. They are more susceptible to disease as the plant is no longer allocating nutrition to those leaves, and because of their proximity to the ground. Foliar diseases that transfer through soil splashing onto lower leaves are likely to begin on lower leaves and move up on the plant. Removing these lower leaves will reduce the amount of new spores produced that are able to move up and infect newer growth.

Remove diseased tomato leaves

Removing diseased plant foliage can reduce infection of healthy tissue.

Suckers are really a new plant- they start at the junction of a leaf and main stem, and will produce flower and fruit if left to grow. Removing them will reduce the ultimate number of fruit that the plant will produce. However, by removing them you reduce the number of fruit, which will increase the size and improve quality of those that remain. Our climate is hot and humid in the summer, with cool nights. This combination is a perfect recipe for long nighttime dews, ideal for propagation of foliar and fruit diseases. This effect is made worse when airflow is limited through the plant canopy. Removing suckers will allow more air to move through the plants, encouraging drying and reducing disease development.

Tomato suckers

Suckers are essentially a new plant growing from the junction of a leaf and stem. Remove when they are 2-6″ in length on a dry sunny day.

So, how should you prune? Some assert that it depends on the type of tomato you are growing. Determinate tomatoes produce most of their fruit in a 4-6 week period and typically grow to a height of 5’ or less. Their apical meristem, or growing point, is a flowering bud. Indeterminate tomatoes produce fruit over a longer period of time. When healthy, this will extend until the first killing frost. Indeterminates have a leaf bud as their apical meristem and can reach heights of 10’-12’ if trellised and healthy. Determinate tomatoes are typically pruned by removing the suckers from up to the first flowering cluster. Indeterminates may have all suckers removed below the second flowering cluster.

Remove suckers when they are 2-6” in length. Suckering- or removing suckers- when suckers are larger can lead to a greater risk of damaging the main stem. Remove all tissue to the junction between leaf and main stem. It is best to do this when plants are dry, and on a dry sunny day. This will reduce disease transfer during the pruning process, reduce potential for infection of plant wounds, and hasten the healing process in the wounds created through suckering. Each time I sucker, I remove lower leaves that show any signs of disease. Completing these tasks together saves time and reduces the number of trips through tomato foliage, once again reducing that potential for human-facilitated disease movement.

Fungal, and to a certain extent bacterial, diseases present substantial challenges for local tomato growers. Not only will blighted leaves reduce plant health and yields, but certain diseases such as anthracnose will damage fruit. We have to anticipate and prevent these diseases if we are to stay ahead of them. Pruning out lower leaves and suckering is a fundamental management step tomato growers should consider in this annual battle.