Pruning tomato plants will speed up your harvest but will also reduce your yield per plant. Pruning, or "pinching back," involves removing suckers, also known as sideshoots. These are the new growths that grow in the V-shape (axil) where a leaf branch and the main stem come together.
Pruning tomatoes isn't necessary for healthy productive plants. You shouldn't need to prune determinate varieties at all. However, you may want to prune your indeterminate tomato plants if your goal is to harvest fruit earlier.
Tomato pruning makes your tomato plants easier to stake and helps produce larger fruits, but it will also reduce the overall season's yield of the plant. Pruning tomato plants to a single main stem is said to be common practice in England.
Pruning encourages earlier fruit production by a week or two.
Pruning encourages larger fruit.
In a high humidity environment or during rainy periods dense foliage can prevent vines and soil from drying which can lead to fruit rot. Pruning excess foliage can help with this.
Pruning a tall indeterminate-type tomato plant to one or two main stems will make it easier to stake.
By training the tomato plant to grow vertically, it takes up less horizontal garden space, making room for more plants.
Some experienced gardeners say pruning doesn't make much of a difference.
Overall tomato yield per plant is reduced.
Pruning indiscriminately can expose stems and leaves to sunscald, particularly if you are in Zone 6 or warmer.
Severe pruning can increase the incidence of blossom end rot.
If you've decided to prune or are unsure how, check out my video demonstration in the article How to prune tomato plants.