The Importance of Pruning Your Tomato Plants

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Introduction | Determinate or Indeterminate?

Tomato plants are broken down into two categories, determinate and indeterminate. Determinate tomatoes bloom all at once and usually do not continue to fruit after the bloom. These types of tomatoes require no pruning above the first set of clusters, so any of the information in this post is generally not adequate for determinate tomatoes. Sources suggest to not prune determinate tomatoes, as pruning will stop potential fruit from blooming. 

Indeterminate tomato plants are plants that grow many vines and bloom pretty consistently until frost. I have found in my experience that these are the best kind of tomatoes for what I am looking to plant, and so I predominantly use indeterminate tomato seeds. If you prefer determinate, go for it, no one is stopping you! I have also read, and I am not sure if this goes for determinate or not, but it is possible to keep indeterminate plants indoors during the cold season in a planter and keep them outside during the warm months for continuous fruiting. I have successfully kept cherry tomato plants in our hydroponics garden this way for about 1 year now and it is still fruiting. 

Why Prune Indeterminates?

Since last year was my first year with a garden, and since certain social media sites were not as established as they are today, I had a hard time finding adequate information on how to care for a garden. One of the things I learned very, very late in the season was about pruning tomato plants. I had one plant in the garden that was about 10 feet tall and 4 feet wide; it was bushy and monstrous. The vines were so long and wild that it was useless to have the cage around it, and the tomatoes that were coming off this supposedly large tomato plant were far from large. What should have been a 1lb fruit was no more than a large cherry tomato, and there were about 50-85 of them on the plant at any given time.

The remedy for this is something called pruning; a technique of trimming unnecessary stalks from the plant in order for it to produce more energy into the fruits than into growing the plant. One of the most beneficial points of the pruning is to allow all of the leaves of the plant to gain sun exposure and to prevent disease that is rampant in damp, dark spaces.

Since a plant that isn't pruned gets to be wild and huge, pruning also gives the plant good shape to well support itself during the growing season, and wont be destroyed by bending stems and by caving in on itself due to its massive size.

Sucker Plants

When pruning a plant, the first stems to go are any that are touching or very close to the soil, as well as something called a sucker plant. Sucker plants are the stems that grow in between the main stem and the first off-shoot of the main stem. A good way to remember this is to hold up your thumb, index, and middle finger. The thumb is the off-shoot, the middle finger is the main cane, and the index finger is the stem you would chop.

Sucker plants often do provide some buds for fruit, however the energy used to create the cane saps the energy necessary to produce large fruits. Overall, it is not worth the effort to keep them on the plant.

How And What To Prune

As mentioned before, any leaves close to the base of the stalk that are touching the soil need to be pruned. Sucker plants can be picked off when they are small, and do not necessarily need pruning shears unless they are larger than 3" to avoid splitting down the spine. Some sources suggest pruning any leaves below the lowest cluster or tomatoes, and always prune any yellow leaves.

I have also read in some sources that suggest keeping 4-6 stems of fruit, which allows a small number to grow, but larger fruits. Nearly all sources suggest keeping stems closest to the fruits to prevent burning while capturing energy from the sun to grow the plant.

Pruning stems require the use of shears and should be on a slant to avoid disease. Always prune dry plants, never prune when the plant is wet or right after a rainstorm. Also, pruning should be done before the plant gets overrun and wild; last year I pruned late in the season and over-pruned my wild plant. It withered and died shortly after due to the shock from pruning so much so quickly.

Conclusion

Pruning is beneficial for indeterminate tomatoes to keep fruits large and the plant healthy. Use shears to cut large suckers off and any branches below the first cluster of fruit, but make sure it's done while the plant is dry and do it early.