Why and when to trim tomato plants

Trimming tomato plants removes leaves, branches, and shoots that don't produce fruit, which lets the plant put energy into the tomatoes that do. A trimmed plant also gets better air circulation around the leaves, which reduces disease and pest problems. Most tomato plants benefit from trimming once they reach about 12 inches tall and have several sets of leaves.

The timing matters. Start trimming in early summer when the plant is actively growing but before the heat of mid-summer stresses it. Stop trimming about four to six weeks before your first expected frost, because new growth that appears late in the season won't have time to mature into fruit.

Key Takeaways

  • Remove suckers (shoots that grow between the main stem and branches) on indeterminate varieties to focus growth on fruit-bearing branches.
  • Prune lower leaves once the plant is established to improve air flow and reduce fungal disease on the soil-facing parts of the plant.
  • Use clean, sharp pruning shears or scissors and wipe the blade with rubbing alcohol between cuts to avoid spreading disease.
  • Determinate (bush) tomatoes need less trimming than indeterminate (vining) types, which can grow several feet tall without pruning.

Removing suckers from indeterminate tomatoes

Suckers are small shoots that sprout in the angle where a branch meets the main stem. On indeterminate tomatoes (the tall, vining types that grow all season), suckers create extra foliage but rarely produce fruit. Removing them channels the plant's energy into the main branches and the tomatoes on them.

Pinch off suckers when they are small—about 2 to 4 inches long—by holding the stem just below the sucker and snapping it off with your thumb and forefinger. If a sucker has grown larger, use clean pruning shears to cut it as close to the main stem as you can. Do this every week or two during the growing season, because suckers grow back quickly.

Determinate (bush) tomatoes produce most of their fruit early and don't grow as tall, so they need little or no sucker removal. If you are unsure which type you have, check the seed packet or plant label—it will say "determinate" or "indeterminate."

Pruning lower leaves to reduce disease

Once your tomato plant is 2 to 3 feet tall and has several sets of leaves, remove the lowest 6 to 12 inches of foliage. These lower leaves are closest to the soil, where fungal spores live and splash up during watering. Removing them stops diseases like early blight and septoria leaf spot from taking hold.

Work your way up the plant over several weeks rather than stripping it bare at once. Remove leaves that show yellow spots, brown patches, or any sign of disease when ready, even if they are higher up. Always cut or pinch the leaf stem where it meets the main branch, leaving no stub behind.

Stop removing leaves once the plant starts flowering heavily. At that point, the leaves feed the developing fruit, and removing too many will reduce your harvest.

Topping the plant to speed ripening

Topping means cutting off the very top of the main stem, which stops the plant from growing taller and tells it to focus on ripening the fruit already on it. This is useful in short-season areas or if frost is coming early. Pinch or cut off the top 4 to 6 inches of the main stem about four to six weeks before your expected first frost date.

Topping works best on indeterminate varieties, which would otherwise keep growing new flowers right up until frost. Determinate plants naturally stop growing and set most of their fruit at once, so topping them is usually unnecessary.

After you top a plant, it may send out new shoots from below the cut. Pinch these off if they appear, because they will not have time to produce ripe fruit before cold weather arrives.

Tools and sanitation

Use sharp pruning shears or clean scissors to make cuts, because dull blades crush the stem and invite disease. For small suckers, your fingers work fine. For anything thicker than a pencil, use shears.

Wipe the blade with rubbing alcohol or a 10 percent bleach solution (one part bleach to nine parts water) between plants or between cuts if you are moving between a diseased plant and a healthy one. Tomato diseases like early blight and fusarium wilt spread on dirty tools, so this step is worth the 30 seconds it takes.

Wash your hands after trimming, and do not touch other plants until you have done so. If you have been handling a diseased plant, change your clothes before working with healthy ones.

What not to trim

Do not remove flower clusters or the branches that bear them. Flowers become fruit, so cutting them off reduces your harvest. If a branch is crowded or shaded by another branch above it, you can remove the entire branch at its base, but leave the flowers on it alone.

Do not strip the plant down to a bare stem. Leaves feed the plant and the developing fruit. A healthy tomato plant should always have plenty of green foliage, even after trimming.

Do not trim during the hottest part of the day or right after rain, when the plant is stressed or wet. Trim in the early morning or late afternoon on a dry day, so the cuts can heal before nightfall.

Frequently Asked Questions

Can I trim tomato plants in the middle of summer?

Yes, but be cautious. Trimming in peak heat stresses the plant. Remove only diseased or damaged leaves and the lowest foliage for disease control. Save heavy sucker removal and topping for early summer or late summer when temperatures are milder.

What should I do with the leaves and branches I remove?

Do not compost diseased leaves or branches—throw them in the trash. Healthy trimmings can go in a compost pile if it reaches 140°F, but most home piles do not get hot enough to kill tomato diseases. When in doubt, discard them.

Will trimming hurt my tomato harvest?

Proper trimming increases your harvest by directing energy to fruit and reducing disease. Removing too many leaves at once or trimming too late in the season can reduce yield, but moderate trimming done early and mid-season improves it.

Do I need to trim cherry tomatoes?

Cherry tomatoes are often indeterminate and grow very tall, so sucker removal helps. Lower leaf removal for disease control is still useful. However, cherry tomatoes are vigorous and forgiving—they will produce well even with minimal trimming.