Pruning Tomato Plants: 6 Mistakes Most First-Time Growers Make

Pruning tomatoes correctly will yield larger, healthier plants that produce more fruit and an earlier harvest. Just be sure to avoid these all-too-common pitfalls.

By Lori Lovely | Updated Apr 6, 2022 12:24 AM

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Tomatoes are America’s favorite garden “vegetable” to grow. Botanically a fruit, the tomato was classified as a vegetable by the U.S. tariff law of 1887 because it’s served with dinner, not as dessert.

Today, there are more than 10,000 varieties in many shapes, sizes, and colors. Given the right conditions—full sun, good soil, adequate water, drainage, and some support, tomato growing is pretty easy.

Plant care includes proper tomato pruning to increase airflow, thereby reducing fungal problems, and to encourage efficient photosynthesis for better growth and bigger yields. But novice gardeners are sometimes guilty of harmful pruning mistakes that can damage the plants and reduce the yield.

The Correct Way to Prune a Tomato Plant

It might seem like a fine line between a perfectly pruned tomato plant and an over pruned tomato plant, but improper tomato pruning can result in problems. If you’re not sure how to prune tomato plants or have had mixed results with tomato pruning in the past, read on for tips.

Simple Pruning

Suckers, which grow in the “V” between the main stem and the branches, need to be pruned to save energy for main branches (and the fruit they produce). It also can prevent the plant from crowding itself and the space around it. Suckers grow quickly, but if left to grow into side stems, they tend to be spindly and produce inferior fruit. When they’re small (under 2 inches), they can be pinched off, but if they’re bigger, pruners are necessary.

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Missouri Pruning

In Missouri pruning, a gardener pinches off or snips only the tip of the sucker, leaving a couple of leaves behind to help protect developing fruit from sunburn. This method is used when things have “gotten out of hand” and a tomato plant has grown large suckers. In this situation, removing just the tip is less of a shock to the plant than removing large side stems, particularly when the weather is hot. The downside is that the remaining portions of the suckers will grow new suckers, requiring ongoing pruning.

Related: This Is the Best Time to Plant Tomatoes

Tomato Pruning Mistakes to Avoid

Pruning is necessary for optimal tomato plant health and yield, so don’t be afraid to prune! Just know the proper way and time to prune a tomato plant to avoid damaging the plant and jeopardizing your harvest. Here are some common tomato-pruning mistakes to avoid.

1. Pruning determinate tomato plants.

Determinate tomato plants don’t need pruning, other than removal of suckers below the first flower cluster. Pruning above the first flower cluster results in loss of potential fruit because determinate tomato plants have a predetermined number of stems, leaves, and flowers hardwired into their genetic structure.

During its initial phase, all stems and most of the leaves form, creating a defined pattern. After the plant flowers and sets final leaf expansion, there’s no additional vegetative growth. Thus, there’s no need for additional pruning. Fewer tomatoes are determinate types, but most are more compact and require less staking. If you are unsure, just search the tomato variety name on a reputable site.

Related: The Best Fertilizers for Tomatoes

2. Pruning when the plants are wet.

Pruning tomato plants when it’s raining or when they’re wet promotes the spread of disease—specifically, bacterial and fungal pathogens. One purpose of pruning tomatoes is to improve air circulation to thwart fungus. To further reduce chances of moisture causing disease (such as tomato blight, a soilborne disease that causes rot), prune the lower leaves of the plant if they are touching the ground, particularly in wet climates where heavy rain saturates the soil.

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3. Pruning with dull or dirty tools.

A pruner, or garden clipper, is the best tool to use on tomato plants. These spring-loaded hand tools can cut stems up to 1 inch in diameter. With use, they can collect dirt, moisture, sap, and debris, which causes them to become dull or rusty. They also can spread disease from one plant to another. Applying a lubricant to the blades helps prevent rust and can make them easier to use.

Re-sharpening the blade with a knife sharpener (or replacing the blades) ensures they’ll give a clean cut. Dull blades will crush the stem rather than cut it, damaging the stem tissue.

4. Waiting too long to prune tomato plants.

If you put off pruning too long, those little suckers will grow into large, heavy branches that can weigh down the plant and prevent sunlight and air from getting to the center of the plant.

When you prune the bigger branches, garden clippers may no longer provide sufficient force; you might need loppers to get the job done. Pruning early when suckers are small is easier. Keep in mind that you’ll have to check and prune repeatedly as new suckers grow.

In addition, those suckers-turned-branches used up a lot of the plant’s energy that could have been diverted to producing more and bigger fruit.

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5. Over pruning.

Over pruning tomato plants removes too many shade-producing leaves, resulting in the fruit being exposed to the hot sun, causing sun scald. Removing more than one-third of the foliage at a time can do more than burn the fruit; it can result in the plant dying. Instead, prune them lightly after they finish setting fruit to keep the plants smaller and encourage new growth, which leads to more flowering and fruiting.

Hint: Tomatoes don’t set fruit in extremely hot temperatures, so the shade from those branches (and maybe some shade cloth) can cool down the tomato plant.

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6. Not topping the main stems at the end of the growing season.

When time is running out at the end of the growing season, topping the growing tips will redirect the sugar the plant is producing to the setting fruit. It should be done about 30 days before the first frost for best results.

Called “topping the plant,” it involves pruning the terminal shoot just above the last blossom, and will help achieve a bigger harvest of red tomatoes, as opposed to mostly green tomatoes as the season winds down. Your pruning will help developing fruit get the nutrients that would have gone into new growth, which is unnecessary this late in the growing season.

Related: When to Pick Tomatoes for the Best-Tasting Homegrown Produce