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Pruning Your Tomatoes

University of Minnesota Extension, Stearns County News
July 12, 2017        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns, Benton, & Morrison Counties


Pruning Your Tomatoes
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (07/12/17) — Pruning your tomato plants may sound crazy, but it is something every gardener should do.  There are numerous disease issues related to growing tomatoes, and one very simple thing all gardeners can do to help reduce the chances of getting and the spread of disease is pruning your plants.

Pruning tomato plants should begin early on in the season and continue throughout, especially with indeterminate plants.  Indeterminate plants are those that continue to produce fruit on new growth throughout the entire growing season until they are killed by frost as opposed to determinate which have a set size and season that they will flower, set fruit, and produce. Pruning is essential to keep good air flow throughout the plant.  Poor air flow can contribute to moist conditions that are more ideal for disease, such as leaf spot.

Leaf spot diseases are primarily caused by fungi and occasionally bacteria. The fungi or bacteria will remain in the area from one season to the next by surviving on infected plant debris or even in the soil.  Unfortunately the spores will then infect new plant material when water splashes the spores upward onto the new plant’s lower leaves. If conditions are right, both wet and warm, the spores will multiply and can eventually infect the whole plant and possibly fruit.

To help prevent leaf spot here are some tips: 1) Inspect plants frequently, and remove any branches that show signs of leaf spot 2) Pinch off lower branches to help reduce any spores existing on plant debris or in the soil from reaching lower leaves 3) Pinch off any suckers that begin growing at the crotch of a leaf and the main stem 4) Use mulch under the plants to help prevent soil and spores from splashing onto the new plant 5) Stake or cage plants to keep all leaves off the ground 6) Weed! Removing weeds in the area will help with air flow and also eliminate possible sources that harbor disease.

In addition to pruning out the suckers and lower stems, it may also be beneficial to prune out stems in the middle part of the plant to also increase air flow. One suggestion would be to prune out any foliage below the first flower cluster that form on the plant.  Keep in mind if you are using a tool to prune, clean the tool between plants; you could be transporting disease from one plant to another. Not only does pruning out additional foliage help with air flow but it also helps the plant focus on putting energy into fruit production rather than foliage.

For more information on tomato disease issues visit

PHOTO: Emerging Tomato Sucker. Photo Credit: North Carolina Cooperative Extension
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Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
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