As we reach the peak of summer, your tomato plants are flourishing and may need some attention to help ensure a bountiful harvest. Pruning tomato plants can help them put more energy into producing fruit instead of growing more leaves. It can also increase the health of the plant by removing interior leaves that aren’t getting much sunlight anyway (therefore not contributing much to photosynthesis) and increasing the airflow through the plant, helping to prevent disease.

How, and even if, you prune your tomatoes will be affected by whether the tomato is an indeterminate or determinate variety.

Pruning Determinate Tomatoes

A determinate tomato is a variety that grows to a predetermined height and stops growing when fruit sets on the top bud. All the fruit ripens near the same time, then the plant stops producing fruit and dies. Most determinate varieties grow in a bush-like profile and reach somewhere between 3 and 4 feet tall. Many sauce tomatoes, like Roma, are determinate varieties. Because of their restricted growth, determinate tomatoes are better adapted to growing in containers.

Pruning is generally unnecessary for determinate tomatoes because they will stop growing on their own. You should prune off any leaves at the bottom of the plant that are close to or directly contacting the soil as these could be vectors for disease.

Because determinate varieties produce all of their fruit at the same time, the plant can be under a heavy load while the fruit ripens. It can be helpful to stake the main stems of your tomato to prevent it from breaking.

Pruning Indeterminate Tomatoes

Indeterminate tomatoes are vines that will grow continuously and produce fruit throughout the season. They generally only stop growing when killed by frost. Some of these plants can reach 10 to 12 feet in length. Because of how large they grow, it is best to provide some sort of trellis to keep the vines off the ground to prevent disease.

Due to the vigorous growth of indeterminate tomato plants, you can improve the harvest from the plant by removing leaves that can block the sun from ripening fruit and take energy from the developing plant.

There are many methods for pruning tomatoes, and no one way is the right way, but there are some things you should consider. As with determinate varieties, it is a good idea to prune off any leaves at the soil level to help prevent disease. You can also remove interior leaves that are not getting much sun. Primarily you should remove what are called “suckers” that appear between the main stem and horizontal leaf branches. Suckers have the potential to become additional branches and will just take resources from the main stem. You can simply pinch suckers off if they are small; otherwise, use sterile shears to trim them. However, you shouldn’t remove suckers right below a blossom, as this can result in uneven growth.

Don’t throw away those larger suckers that you’ve trimmed off. You can plant those in soil up to the first leaf on the stem. The cutting will produce roots and become another tomato plant. This can be useful in case your original plants fail due to pests or diseases.

Because indeterminate varieties don’t stop growing, you should pay attention to the weather. You should “top” your tomato plants as the end of the season nears to encourage the plant to put energy into the fruit already on the vine rather than producing more foliage. Topping means removing the terminal shoot just above the last blossom. Be sure to harvest any fruit before frost – even still-green tomatoes should be harvested to prevent loss. You can leave them to ripen on a sunny windowsill or in a paper bag.

Some Other Things to Consider

• Avoid pruning when plants are wet or it is raining, as this can promote the spread of bacterial or fungal diseases.
• Use sharp, clean tools when pruning to prevent damage and disease. Clean tools with rubbing alcohol or bleach after each plant.
• Don’t wait too long to prune. Waiting too long to remove suckers means the plant has wasted energy on unnecessary leaves instead of fruit.
• Don’t over-prune. Tomato fruit still needs some shade for protection from sun scald while ripening. Never remove more than one-third of the foliage at a time, or you may kill the plant.

You’ve watered, fertilized, and lovingly tended your tomatoes all season. Help ensure the best possible harvest with careful pruning.