Why and when to prune tomato plants

Pruning tomato plants removes unnecessary growth so the plant puts energy into producing fruit instead of leaves and branches. A pruned plant also gets better air circulation, which reduces disease and makes harvesting easier. Most tomato plants benefit from pruning, though the timing and method depend on whether you are growing a determinate variety (bush type that grows to a set size and produces most fruit at once) or an indeterminate variety (vine type that keeps growing and producing fruit all season).

Start pruning indeterminate tomatoes when they are about 12 inches tall and the first flower clusters are visible. Determinate varieties need less pruning—usually just removing the lowest leaves once the plant is established. Prune on a dry day, ideally in the morning, so cuts dry quickly and are less likely to invite disease.

Key Takeaways

  • Indeterminate tomatoes need regular pruning to remove suckers (shoots between the main stem and branches), while determinate varieties need minimal pruning.
  • Remove the lowest leaves once the plant is 12 to 18 inches tall to improve air circulation and reduce soil-borne disease.
  • Prune on a dry day using clean, sharp pruners or scissors, and sterilize your tools between cuts to prevent spreading disease.
  • Stop pruning indeterminate varieties about four weeks before your first expected frost so the plant can focus on ripening existing fruit.

Removing suckers from indeterminate tomatoes

A sucker is a shoot that grows in the angle between the main stem and a branch. Indeterminate tomatoes produce many suckers, and removing them directs the plant's energy toward fruit rather than foliage. Suckers are easiest to remove when they are small—less than 2 inches long—because you can pinch them off by hand without tools.

To remove a sucker by hand, hold the main stem steady with one hand and pinch the sucker at its base with your thumb and forefinger, bending it back and forth until it snaps off. If the sucker is larger than 2 inches or too woody to pinch, use a clean, sharp pruner to cut it as close to the stem as possible. Check your plants every 7 to 10 days during the growing season, because new suckers appear constantly on indeterminate varieties.

Do not remove all the leaves and branches—leave the main stem and the primary branches intact. The goal is to thin the plant, not strip it bare. A plant with no leaves cannot photosynthesize and will stop producing fruit.

Removing lower leaves to prevent disease

Once your tomato plant is 12 to 18 inches tall, remove the lowest 6 to 8 inches of leaves from the main stem. These lower leaves are closest to the soil, where fungal spores and bacteria live. Removing them improves air circulation around the base of the plant and reduces the chance of early blight, septoria leaf spot, and other soil-borne diseases that spread upward.

Use clean pruners to cut the leaf stems (petioles) where they meet the main stem. Make a clean cut—do not leave a stub. Remove leaves gradually over a week or two rather than all at once, so the plant does not lose too much photosynthetic capacity at one time. As the plant grows taller, continue removing the lowest leaves so there is always at least 6 inches of bare stem between the soil and the lowest leaf.

Pruning the top of the plant before frost

About four weeks before your first expected frost date, stop removing suckers and instead pinch off the top of the main stem and all the branches. This is called topping, and it tells the plant to stop growing taller and focus on ripening the fruit already on the vine. Fruit that has not set by this point will not have time to mature before cold weather arrives.

To top the plant, pinch or cut off the growing tip of the main stem and each primary branch, removing about 1 inch of new growth. The plant will not produce new flowers after topping, but the existing fruit will ripen faster because the plant is no longer dividing its resources between growth and fruit production. This step is especially important in areas with short growing seasons.

Tools and sanitation

Use sharp pruning shears or pruning scissors for cuts larger than what you can pinch by hand. Dull tools crush the stem instead of cutting cleanly, which invites disease and slows healing. Bypass pruners (the kind with one sharp blade that cuts against a flat surface) work better than anvil pruners (which have two blades that meet) because they make cleaner cuts.

Sterilize your tools before you start pruning and between plants if you are working in a garden with multiple tomato plants. Wipe the blades with a cloth soaked in rubbing alcohol, or dip them in a 10 percent bleach solution (1 part bleach to 9 parts water) for 30 seconds, then rinse with clean water and dry. This prevents spreading disease from one plant to another.

Pruning determinate (bush) tomatoes

Determinate tomatoes grow to a fixed height and produce most of their fruit in a short window, so they need much less pruning than indeterminate varieties. In fact, heavy pruning can reduce your harvest because you are removing branches that would have produced fruit. Limit pruning to removing the lowest leaves once the plant is established, and remove any diseased or damaged branches.

You can also remove a few suckers if the plant becomes very dense and air circulation is poor, but do not make it a routine practice. The plant's natural bushy shape is part of its design. If you want to grow a determinate tomato with minimal maintenance, straightforward let it grow and harvest when the fruit ripens.

Common pruning mistakes to avoid

Removing too many leaves at once starves the plant of the energy it needs to produce and ripen fruit. If you strip a plant down to bare branches, it will stop growing and may drop its flowers. Remove leaves and suckers gradually, and never remove more than one-third of the plant's foliage in a single week.

Pruning on a wet day or when the plant is wet spreads fungal spores and bacteria from one cut to the next. Wait for a dry day, and make sure the foliage has dried after rain or watering before you start. Leaving stubs when you cut also invites disease—always cut as close to the stem as possible so the plant can heal quickly.

Pruning too late in the season wastes the plant's energy on growth that will not mature before frost. Stop pruning indeterminate varieties four weeks before your first expected frost, and do not prune determinate varieties at all once they start flowering heavily.

Frequently Asked Questions

Can I prune tomato plants in the afternoon?

Morning is better because the plant has all day to dry and heal before nightfall, which reduces disease risk. If you must prune in the afternoon, do it early enough that the cuts have several hours of daylight left to dry before evening.

What do I do with the leaves and suckers I remove?

Do not compost diseased leaves or suckers—throw them in the trash. Healthy prunings can go in a compost pile if your compost reaches 140°F or higher, which kills most pathogens. If you are unsure whether your compost gets hot enough, discard the material instead.

Will pruning hurt my tomato plant?

No, pruning actually helps the plant by directing energy toward fruit and improving air circulation. Tomato plants are tough and recover quickly from pruning. The key is to prune gradually and avoid removing so much foliage that the plant cannot photosynthesize.

Do I need to seal the cuts with wound dressing?

No. Tomato plants heal best when cuts are left open to air. Wound dressing can trap moisture and actually increase the risk of disease. A clean cut on a dry day is all the plant needs.

When should I stop pruning for the season?

Stop pruning indeterminate tomatoes about four weeks before your first expected frost date. For determinate varieties, stop pruning once heavy flowering begins. After that point, the plant needs all its energy to ripen fruit, not heal from pruning wounds.