Why and when to trim tomato plants
Trimming tomato plants removes growth that steals energy from fruit production and improves air flow around the plant, which reduces disease. The two main reasons to trim are to remove suckers (shoots that grow between the main stem and branches) and to thin out dense foliage so sunlight reaches the fruit and lower leaves dry quickly after rain.
Start trimming once the plant is about 12 inches tall and has its first true leaves. Continue trimming throughout the growing season, but stop about four weeks before your first expected frost—late trimming removes leaves the plant needs to ripen remaining fruit. Determinate varieties (bush types that grow to a set size) need less trimming than indeterminate varieties (vining types that grow all season).
Key Takeaways
- Remove suckers—the shoots growing between the main stem and side branches—by pinching them off by hand when they are small, before they waste plant energy.
- Trim lower leaves once the plant is established to improve air circulation and prevent soil-borne diseases from splashing onto foliage during watering.
- Thin out dense foliage in the upper canopy so sunlight reaches developing fruit and leaves dry quickly after rain.
- Stop trimming four weeks before your first frost date so the plant can focus energy on ripening the fruit already on the vine.
- Use clean pruning shears or pinch suckers by hand; wash your hands between plants to avoid spreading disease.
How to identify and remove suckers
A sucker is a small shoot that grows in the crotch where a branch meets the main stem. It looks like a miniature version of the main stem and will grow into a full branch if left alone. Removing suckers early—when they are 2 to 4 inches long—takes seconds and prevents them from becoming thick woody growth that shades fruit.
Pinch suckers off by hand between your thumb and forefinger, or use clean pruning shears if they have hardened. The best time is early morning when the plant is firm and the sucker snaps cleanly. If you miss a sucker and it grows thick, cut it as close to the main stem as you can. Do not leave a stub, because it will regrow.
Indeterminate varieties produce suckers constantly all season, so check your plants every few days during peak growing months. Determinate varieties produce fewer suckers and stop growing after reaching their set height, so they need less frequent attention.
Removing lower leaves to prevent disease
Once your plant is 18 to 24 inches tall and has set its first fruit, remove the lowest 6 to 8 inches of leaves. These leaves are closest to the soil, where fungal spores and bacteria live. When you water, soil splashes onto these lower leaves and introduces disease. Removing them stops the cycle before it starts.
Work your way up the plant over several weeks rather than stripping all lower leaves at once. Remove one or two leaf sets every few days. This gives the plant time to adjust and keeps enough foliage to feed the fruit. Stop removing lower leaves once the plant is about 3 feet tall—below that point, the risk of disease is highest.
Make your cuts close to the stem so no leaf stub remains. Wash your hands or dip your pruning shears in a 10 percent bleach solution (one part bleach to nine parts water) between plants to avoid spreading fungal disease from one plant to another.
Thinning the upper canopy for sunlight and air flow
Dense foliage in the upper part of the plant shades developing fruit and traps moisture, creating conditions where fungal diseases thrive. Once the plant has several branches with fruit forming, thin out some of the leafy growth so you can see through the canopy to the fruit inside.
Remove entire leaf sets rather than cutting leaves in half. Start with leaves that are yellowing, diseased, or damaged—these are not feeding the plant anyway. Then remove leaves that shade fruit clusters, working from the outside of the plant inward. Aim to remove no more than 10 to 15 percent of the foliage at one time.
The goal is dappled light reaching the fruit, not bare branches. Tomato fruit can sunscald if exposed to intense afternoon sun without any leaf protection, especially in hot climates. If you live in a region with very hot summers, be conservative with upper canopy trimming.
Tools and sanitation
Use bypass pruning shears (the kind with two blades that pass each other, like scissors) for clean cuts. Anvil shears (one blade pressing down onto a flat surface) crush stems and leave ragged edges where disease can enter. Keep shears sharp so they cut cleanly rather than tearing.
Wash your hands or dip your shears in a 10 percent bleach solution between plants. Tomato diseases like early blight and septoria leaf spot spread on tools and hands, so sanitation is the cheapest disease prevention you have. If a plant shows signs of disease (brown spots, yellowing, wilting), trim it last so you do not carry the problem to healthy plants.
Pinching suckers by hand is also fine—many gardeners do this and never use shears. Wash your hands before moving to the next plant if you are pinching off diseased growth.
What not to trim
Do not remove the main growing tip at the top of the plant unless it is diseased or damaged. That tip is where the plant produces new flowers and fruit. Cutting it off stops vertical growth and can reduce your total harvest.
Do not strip all the leaves off a branch to expose fruit. Leaves feed the fruit and protect it from sunburn. Thin foliage, do not remove it entirely. If a branch has no leaves left, it cannot ripen the fruit on it, so that fruit will stay green.
Do not trim heavily in late summer. Four weeks before your first frost date, stop removing foliage so the plant can direct all its energy into ripening the fruit already on the vine. Trimming late in the season removes the leaves the plant needs to finish that job.
Trimming determinate versus indeterminate varieties
Determinate (bush) tomatoes grow to a set height—usually 3 to 4 feet—and stop. They produce most of their fruit in a short window, then decline. These plants need minimal trimming: remove suckers if they appear, and thin lower leaves for disease prevention. Do not aggressively thin the canopy, because the plant does not have all season to regrow foliage.
Indeterminate (vining) tomatoes grow all season until frost kills them. They can reach 6 feet or taller and produce fruit continuously. These plants benefit from regular sucker removal and more aggressive canopy thinning because they have time to regrow foliage and will produce more fruit if light and air flow are good. Many gardeners trim indeterminate plants more heavily than determinate ones.
Check the seed packet or plant label to know which type you have. If you are unsure, indeterminate varieties usually have a longer harvest window listed, while determinate varieties say "determinate" or "bush" on the label.
Frequently Asked Questions
Can I trim tomato plants in the heat of the day?
Early morning is best because the plant is firm and cuts heal faster. Trimming in intense afternoon heat stresses the plant. If you must trim during the day, water the plant well beforehand so it is not already stressed.
What should I do with the leaves and stems I remove?
Do not compost diseased leaves or stems—throw them in the trash. Healthy trimmings can go in a compost pile if it reaches 140°F or higher, which kills most disease spores. If you are unsure whether your pile gets hot enough, trash is the safer choice.
Will trimming reduce my tomato harvest?
Proper trimming increases harvest by improving air flow and directing energy to fruit production. Removing suckers and lower leaves does not reduce the number of fruit—it improves the health of the plant so it produces more ripe, disease-free tomatoes.
How much foliage can I safely remove at once?
Remove no more than 10 to 15 percent of the plant's foliage in a single session. The plant needs leaves to feed itself and the fruit. Removing too much at once stresses the plant and can slow growth and ripening.
Do I need to seal the cuts with wound dressing?
No. Tomato plants heal cuts on their own, and wound dressing can trap moisture and invite disease. Make clean cuts and leave them alone—the plant will seal them naturally.