Why and When to Prune Tomato Plants
Pruning tomato plants removes unnecessary growth so the plant puts energy into fruit instead of leaves and branches. A pruned plant also gets better air circulation, which reduces disease and makes harvesting easier. You start pruning once the plant is about 12 inches tall and has its first true leaves—usually 3 to 4 weeks after planting.
The timing depends on your tomato type. Determinate (bush) varieties grow to a set size and produce most fruit at once, so they need light pruning or none at all. Indeterminate (vining) varieties grow all season and benefit from regular pruning every 1 to 2 weeks. Check your seed packet or plant label to know which type you have.
Key Takeaways
- Indeterminate tomatoes need regular pruning to focus growth on fruit; determinate varieties need little to no pruning.
- Remove suckers (shoots between the main stem and branches) when they are small, before they steal energy from fruit-bearing branches.
- Prune in the morning when the plant is dry, and use clean, sharp pruners to avoid spreading disease between cuts.
- Stop heavy pruning 4 to 6 weeks before your first expected frost so the plant can ripen remaining fruit.
- Remove lower leaves once fruit sets to improve air flow and reduce fungal disease on the soil.
Removing Suckers from Indeterminate Tomatoes
A sucker is a small shoot that grows in the angle (called the crotch) between the main stem and a branch. On indeterminate plants, suckers grow constantly and waste energy that could go to flowers and fruit. Pinch or cut them off when they are 2 to 4 inches long—they come off easily at this size and cause less damage to the plant.
Look at the plant from the side and trace the main stem upward. Where each branch meets the stem, you will see a small shoot growing at an angle. That is the sucker. Use your thumb and forefinger to pinch it off, or use pruning shears if it is woody. Do this every 1 to 2 weeks during the growing season. On determinate plants, skip this step—the plant is designed to grow bushy, and removing suckers will reduce your harvest.
Pruning Lower Leaves and Improving Air Flow
Once your tomato plant has set fruit (small green tomatoes are visible), remove the lowest 6 to 8 inches of leaves. These lower leaves touch soil and splash, which spreads fungal diseases like early blight and septoria leaf spot. Removing them also lets air move under the canopy, drying the remaining leaves faster after rain or watering.
Work your way up the plant, removing any leaves that are yellowing, spotted, or touching the ground. Leave the upper leaves and the leaves closest to developing fruit—those feed the plant and the tomatoes. Make cuts close to the stem so you do not leave a stub. Do this pruning in the morning when the plant is dry, and wash your hands and pruners between plants to avoid spreading disease.
Thinning Branches on Overgrown Plants
If your indeterminate tomato becomes very dense with branches and leaves, thin out some of the older, less productive branches to let light and air reach the fruit. Look for branches that are shaded by others or that have few flowers or small fruit. Cut these branches back to the main stem using clean pruning shears.
Do not remove more than one-third of the plant's foliage at once—the leaves are what feed the fruit. Spread thinning over several weeks if the plant is very overgrown. Thinning is less critical than removing suckers and lower leaves, but it helps in humid climates where disease pressure is high.
Stopping Pruning Before Frost
Stop heavy pruning 4 to 6 weeks before your first expected frost date. At this point, the plant needs all its leaves to ripen the fruit already on the vine. Pruning late in the season removes the energy source the tomato needs to mature and sweeten.
You can still remove diseased or dead leaves right up to frost, but do not cut back branches or remove healthy foliage. If you live in a warm climate with a long season, you may prune lightly all the way through summer, but always ease off as temperatures cool in fall.
Tools and Technique to Prevent Disease
Use sharp pruning shears or your fingers for small suckers. Dull blades crush the stem, creating wounds that invite disease. Bypass pruners (the kind with two blades that pass each other) work better than anvil pruners (one blade pressing onto a flat surface) because they make a cleaner cut.
Prune in the morning when the plant is dry. Wet foliage spreads disease spores easily, and wet wounds heal slower. After each cut on a different plant, wipe your blade with a cloth dampened in rubbing alcohol or a 10 percent bleach solution (one part bleach to nine parts water). This takes 30 seconds and stops you from moving disease from a sick plant to a healthy one.
Common Mistakes to Avoid
Do not prune determinate (bush) tomatoes heavily. These varieties are bred to grow bushy and produce most of their fruit in a short window. Heavy pruning removes branches that will bear fruit and lowers your total harvest.
Do not prune too late in the season. Pruning in late summer or early fall removes leaves the plant needs to ripen remaining fruit. The tomatoes will stay green longer and may not ripen before frost arrives.
Do not remove all the leaves at once, even on an overgrown plant. The leaves feed the fruit. Removing more than one-third of the foliage in a single session stresses the plant and can sunscald the fruit (white or yellow patches where the sun burns exposed skin).
Do not leave stubs. Cut branches and suckers as close to the main stem as possible. A stub left behind is a wound that does not heal well and invites disease.
Frequently Asked Questions
Do I have to prune my tomato plants?
Determinate (bush) varieties do not need pruning and will produce fine without it. Indeterminate (vining) varieties produce more fruit and stay healthier with regular sucker removal and lower leaf pruning, but they will still produce if you do not prune. Pruning is most important in humid climates where disease pressure is high.
What is the difference between a sucker and a branch?
A branch grows from the main stem and has flowers and fruit on it. A sucker is a small shoot that grows in the angle between the main stem and a branch and does not produce fruit. Suckers steal energy from the branches that do bear fruit.
Can I prune my tomato plant in the afternoon or evening?
Morning is best because the plant is dry and wounds heal faster. Pruning wet plants spreads disease spores and creates wounds that stay wet longer. If you must prune in the afternoon, wait until the foliage is completely dry.
Will pruning my tomato plant delay the harvest?
No. Pruning indeterminate tomatoes actually speeds up ripening because the plant puts energy into fruit instead of excess foliage. You may see fewer total tomatoes on a heavily pruned plant, but the ones that grow will be larger and ripen faster.
What should I do with the leaves and branches I remove?
Do not compost diseased leaves or branches—throw them in the trash. Healthy prunings can go in a compost pile if your pile reaches 140°F (60°C), which kills most disease spores. If you are unsure, trash them to be safe.