Stop Ruining Your Tomato Plants with This Common Pruning Mistake!

My first garden in my early 20s proved that I could grow big bountiful tomato plants rife with thick foliage, tons of branches, and promising flowers. They were so big and so beautiful with lush green leaves I couldn’t bring myself to prune them.

One day I came home from work to find my mother had stopped by and pruned them for me. She didn’t just gently sucker back the unnecessary shoots like you’re supposed to do when you prune your tomatoes. She went after them like a slasher film, hacking up my tomato plants like a masked villain with a machete chopping up a recently deflowered camp counselor.

Many of the main branches were broken, and some branches weren’t cut clean, causing the plant to weep fluid. Many plants became vulnerable to fungal diseases before their fruit ripened. It ended up devastating my harvest.

Setting aside the terse conversation I had with my mother, there were some lessons to be learned here. There is a correct time and technique for pruning tomatoes. If you aren’t careful, pruning your tomatoes wrong can destroy your harvest.

What Is Tomato Pruning?

In the parlance of tomatoes pruning, or suckering, is the process of selectively removing excess branches before they flower and set fruit. It’s intended toencourage the tomato plant to keep its energy focused on developing its existing fruit without diverting resources to developing new clusters of unripe tomatoes.

With certain types of tomatoes, this pruning technique gives you larger fruits that ripen slightly faster. You also tend to have less wasted unripe fruit at the end of the season.

However, there are benefits to pruning that go far beyond actual tomato production.

Why Prune Tomato Plants?

The biggest benefit of pruning tomato plants isn’t to boost the size of the fruit. It’s actually to keep the plant strong and supported enough to keep providing healthy fruit.

Maintaining Control & Support

Tomatoes are technically a type of vine, that evolved to sprawl across the jungle floor. Many indeterminate tomatoes will outgrow their cages and other support structures. The same cage that once held the tender seedling upright can later become the hard point that bends and breaks an untamed main branch.

Reducing the Risk of Fungal Problems

An overly bushy tomato plant can harbor excess moisture and humidity that mold, blight, and airborne fungal spores can exploit. This is a common problem with apple trees and one of the reasons why you prune them to have an open center.

You can use a modified version of this to let in a little lighter in the center and lower branches of the tomato plant and improve airflow. Both of which will reduce the risk of fungal diseases attacking the plant.

You just have to make sure you’re not pruning the tomato plant so much that the fruits are at risk of severe sunscald and cracking from excess sunlight exposure.

Improve Size & Ripening Time

Some tomatoes will give you larger fruit that ripens a little faster when properly pruned. This tends to be globe-style tomato varieties like beefsteak, mortgage lifter, and Brandywine.

Drought Resistance and Less Cracking

Inconsistent soil moisture, watering problems, and dry soil can lead to cracking in large tomatoes. By strategically pruning the tomato plant to optimize the shade exposure of the soil, while minimizing lingering moisture on the upper branches can help reduce dry soil problems.

Larger Fruits

Pruning helps indeterminate tomato plants develop larger fruits. Reducing the number of fruits that are receiving water and nutrients, the plant is encouraged to put those resources into the globes.

Earlier Ripening Fruit

When you prune tomato plants correctly, the plant is also encouraged to put more resources into ripening the fruits. As the season goes on, the growing fruits of a short-day indeterminate tomato plant will accelerate the process of converting starch to sugars when the plant is properly pruned.

Less End-of-Season Waste

When you correctly prune a tomato plant to optimize its fruit production and ripening, you end up with less wasted unripe “Green” tomatoes at the end of the season. Especially if you’re diligent about “Topping” your tomato plants in the last 4 to 6 weeks of the summer growing season.

It’s especially helpful in northern growing zones where a freak frost in early fall can bring an abrupt end to your growing season.

What Tomatoes Need Pruning

Tomatoes that benefit from pruning the most tend to be indeterminate globe varieties. This includes things like beefsteak, early girl, mortgage lifter, and Brandywine.

Plum-style tomatoes like Roma, San Marzano, Amish Paste, and Polish linguicadon’t necessarily need to be pruned. Unless they’re sprawling out so much that you can’t support them properly.

In northern growing zones from 5A and colder, you might want to prune or “Top” your tomatoes in mid-August. This will encourage the plant to develop and ripen the existing fruits before a snap frost ends the growing season.

Cherry tomatoeswon’t develop larger fruit or ripen any earlier when pruned. The only time pruning matters to them is if they’re sprawling out of control. The last thing you want is a kink in a main vine killing dozens of green cherry tomatoes before they have a chance to ripen.

Determinate tomatoes don’t need pruning at all. They ripen their fruit all at the same time and tend to develop smaller plants that rarely ever outgrow their support structure.

When to Prune Tomatoes

The timing of when you prune your tomatoes will have a major impact on your harvest. There are several strategic times to consider.

Early Pruning

Early pruning when tomato plants are youngis usually done when the plants are about 12 to 18 inches tall. Here you’re suckering back small weak branches to strengthen larger ones that are capable of producing and supporting stronger fruits.

Early pruning is also about training your tomato plants for your chosen support structure. The strongest branches are then integrated with the cage, Florida weave, or other support system you intend to use.

Maintenance Pruning

You want to keep maintenance pruning in the season to a bare minimum, or you risk a reduced harvest. You shouldn’t do any serious maintenance pruning until after June 21^st when the short-day trait of most indeterminate tomatoes starts to affect plant growth, flowering, and fruit set.

Even then maintenance pruning is meant more for keeping the plant from escaping the support structure or perhaps correcting an area of extreme overgrowth near the center of the foliage.

Late Season Pruning

Late-season pruning of your tomato plants, known as “Topping” will have a major impact on your harvest. By suckering smaller unproductive vines more of the plant’s energy goes into developing and ripening the existing fruit.

In northern growing zones with a risk of freak frosts in late summer and early fall, pruning your tomato plants in the last 4 to 6 weeks of the growing season can boost your harvest by up to 20 to 25%. While reducing the number of green/wasted tomatoes left on the vine.

How to Prune Tomato Plants Correctly

The best way to prune your tomato plants correctly, without destroying your harvest starts with using a very sharp scissors or a pruning shears meant for flowers.

You want to target the small shoots that develop in the crotches between the main stem and thick secondary branches of tomato plants. You often find them where a branch meets the main stem. They often start out looking like little leaves or tiny light green branches.

Then make a clean cut that’s flush with the main stem. The goal is to create a smooth surface, which the plant’s natural pectin will seal cleanly, much like how your own platelets create a scab.

Pro Tip

Any ragged edges or large wounds on the stem can seriously hamper your harvest as they create areas that fungus and other diseases can exploit. The plant ends up losing a lot of production to blight, and decreased photosynthesis which is far worse than if you just let the suckers alone in the first place!

Frequently Asked Questions

Should I prune wilted or diseased branches?

Pruning wilted or diseased branches off your tomato plant is an ineffective strategy for preventing the spread of the disease. By the time you notice signs of fungal blight or plant-borne viruses the presence is already spreading through the plant.

Pruning compromised branches leaves a wound that makes it easier for the pathogen to get deeper into the plant. As long as the top of the tomato plant is growing vigorously, you likely still have several weeks of production before it kills the tomato outright.

Conclusion

An incorrect tomato pruning strategy can destroy more of your harvest than if you left the suckers in place. When it comes to pruning tomato plants for fruit production and larger fruits, you only really need to do it with indeterminate varieties that produce globes of “Slicer” tomatoes.

However, you might need to prune indeterminate paste/plum tomatoes and cherry tomato plants to keep them trained for the support structure you have in place. An untamed tomato plant like this can suffer a massive decrease in the harvest if the branches kink or break from poor support.

When pruning your tomatoes, you should use a sharp scissors, small pruning shears or a box cutter. This will create a clean cut that heals easily, with less risk of diseases exploiting the wounded area. Especially since a ragged cut that lets fungal diseases into the plant can devastate your harvest in weeks!