Pruning and trimming tomato plants is an excellent way to keep them healthy and pest free. Removing excess plant material allows increased air circulation around and into the center of the tomato plant. It also encourages the tomato to focus on producing fruit, which leads to earlier (by 2 to 3 weeks) and larger fruit. Tomato plants come in two varieties: indeterminant and determinant. Indeterminant tomato plants grow and set fruit until killed by disease or frost. Determinant tomato plants reach a set height (usually before producing fruit), and their fruit is set and ripens over a 2-to-3-week period. Indeterminant tomato plants need more pruning and trimming than determinant varieties.
Wait to prune your tomato plants (both determinant and indeterminant varieties) until the plant begins to produce flower clusters.
Remove all the leaves and stems below the lowest flower cluster. Make pruning cuts as close to the main stem as possible. This is the only pruning you need to do to determinant tomato plants.
Keep the suckers (small shoots) that are growing from the first, second and third nodes (the y-shaped space between side stems or leaves and the main stem) above the lowest flower cluster intact. These suckers will grow into fruit bearing stems. The goal is to produce a tomato plant with three to four sturdy stems.
Prune off all other suckers. Continue doing this throughout the growing season.
Trim off dead, discolored or yellowing leaves and wilting or yellowing side shoots. This is done to both determinant and indeterminant varieties.
Prune off the top of indeterminant tomato varieties four weeks before the first predicted frost date. Make the pruning cut 2 to 3 inches above the highest fruit cluster. This is called topping the tomato plant and allows the plant to focus on ripening set tomatoes rather than continued production.