Pruning is usually a term associated with trees or shrubs, but pruning tomato plants can be very important. When pruning a tomato plant you are pruning what are called “suckers.”Suckers are small shoots that grow out of the joint where a branch on a plant meets the stem. The joint will be in the shape of a V and if a sucker is growing it will be more in the shape of a W. You do not want to allow suckers to grow to form the W. These small shoots will eventually grow into a full size branch if left alone, which will result in a bushier, more sprawling tomato plant, but will not harm your plant. Typically, this should from the time the plant is small, but if you are finding yourself with a jungle of tomato plants, it’s not too late to start.
Pruning will promote fruit growth and allow better air circulation throughout the plant. By pinching off the sucker branches, less of the plants energy will be directed toward producing and maintaining foliage and will result in more energy being directed toward producing larger fruit that will ripen sooner. However, some studies do not recommend pruning because sucker branches will actually produce fruit. Your result may be larger amounts of smaller fruits versus larger fruits. So, it really is a personal decision on if you want to prune.
You want to make sure to prune during a dry, sunny day. Anytime you are pruning it causes an opening into the plant that is an area where disease can get in. This is similar to cutting yourself and having an open wound. If you use scissors or pruners instead, be sure to sanitize them before and after use to make sure there is no transfer of disease.