Pruning is the removal of suckers. Suckers are small stems that grow between the main stem and the leaf axil.
Benefits of Pruning Suckers
Suckers are primarily vegetative (and do not produce much, if any, fruit). Leaving them on means the plant devotes a lot of energy to growing suckers instead of producing more fruit. Removing suckers can also open up the canopy to allow for better air circulation, helping to reduce the potential for foliar diseases.
How to Remove Suckers
To remove suckers, identify the main stem. Follow it up from the base of the plant. At each junction (node) grows a compound leaf. In between those two structures you can find a new stem developing. That stem is the sucker. Simply snap off with your fingers or prune out with sharp pruners the sucker when it is small (less than a few inches long).
For determinate tomatoes, remove suckers up to the first cluster of flowers. There is no need to remove suckers above that point on the main stem. Yields do not increase by removing suckers beyond the first flower cluster on determinate tomatoes. For indeterminate tomatoes, continue to remove suckers as they form all along the main stem throughout the growing season.
Tips
It is not necessary to remove every sucker on the main stem, especially if it leaves the leaf canopy very open. When there is not enough foliage, it can cause tomatoes to be exposed to bright sunlight and develop sunburn or sunscald, which will damage the fruit.
Disinfect your hands and pruning equipment, especially if you smoke or use tobacco. Clean your hands or tools in between plants or every few plants to help prevent the accidental spread of diseases.
Snap or cut the sucker cleanly from the plant. Do not leave behind a jagged wound.
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