Tomato pruning mistakes: 9 pruning mistakes to avoid in your garden

Tomato are a popular garden crop for their high productively and rich flavors, and learning to grow them well includes understanding how to prune the plants. Fear of tomato pruning mistakes holds many gardeners back from trimming their tomato plants. But this is a task worth learning as properly pruned tomato plants are healthier, bothered by fewer fungal diseases, and more productive. Keep reading to get our in-depth advice on common tomato pruning mistakes to avoid. 

Why prune tomato plants?

There are many reasons to prune tomato plants. Pruning helps the gardener direct growth and control the mature size of the plant, as well as fit more plants into the garden, maximizing space. Tomato pruning to promote airflow can boost plant health and reduce the occurrence of diseases. Removing unnecessary growth also prevents over-crowding and permits lots of sunlight to reach the center of the plant. Pruned plants may crop earlier than unpruned plants and produce larger fruits. 

9 tomato pruning mistakes to avoid in your garden:

1) Pruning determinate tomatoes

“Should I prune determinate tomatoes?” is a common question. The answer is no. Determinate, or bush, tomatoes aren’t pruned. Why? It’s because these plants have a pre-determined height and when they reach that size, they stop putting on leafy growth and focus on flowering and fruit set. If you remove suckers or branches from determinate tomatoes you’re reducing their fruiting capacity. It’s best to take a hands off approach to pruning determinate tomatoes. 

That said, I do remove the bottom leaves on my determinate tomatoes so the foliage doesn’t touch the ground. Removing lower leaves can reduce or slow the spread of soil-borne diseases like early blight. Use pruning shears or garden snips to cut off those leaves 

2) Not pruning indeterminate tomatoes is a common tomato pruning mistake

Indeterminate tomatoes are also known as vining tomatoes and the vigorous plants can grow 6 to 7 feet tall. They’re typically staked or supported to keep the plants off the ground. New growth is tied or clipped to the stake regularly. When pruning a tomato on a stake the goal is to control growth and encourage good air flow.

Tomato suckers are sideshoots that grow from the angle where the leaf of a tomato meets the stem. Tomato suckers produce flowers and eventually fruits, but allowing all the suckers to grow on an indeterminate tomato isn’t a good idea. It results in a massive, overgrown plant that’s difficult to support, but is also more prone to insect problems and plant diseases. 

A tangled tomato plant is dense with leaves and that creates shade in the middle of the plant. Shade slows how quickly moisture dries from the leaves after a rain and too much shade can slow fruit ripening too. Ideally, all the leaves on a tomato plant should have access to light which is why I remove the majority of the suckers that form on my indeterminate plants.

3) Removing all of the tomato suckers

We now know that leaving every sucker on an indeterminate tomato isn’t a good idea. That said, we also don’t want to remove all of them. My approach is to take out the suckers that form below the first flower cluster. The bottom suckers are less productive and can crowd the plant and reduce airflow. The exception to this is the one sucker that forms just below that first flower cluster. I leave this one as it tends to be a vigorous and productive shoot.

It’s generally recommended that staked indeterminate plants have between 1 and 4 stems. Plants trained and pruned this way will have fewer fruits than an unpruned tomato, but they will be larger and the plants healthier. Stem 1 is the main stem. Stem 2 is the sucker below the first flower cluster. And if you want more than 2 stems, let one or two of the suckers just above the first flower cluster develop. After you have the number of stems you want, pinch out all other suckers. Small suckers are easily removed by hand, but if you wait too long they are harder to snap off and you may damage the plant. At that point, use garden snips to clip them out.

However, don’t be in a rush to prune out the bottom suckers. It takes a few weeks from planting to know where the first flower cluster will appear. Wait until it does so that you can clearly see which suckers to remove.

4) Not pruning tomato plants at all

Early blight, or Alternaria, as well as Septoria leaf spot are two common fungal diseases that affect tomato plants. There are several ways for gardeners to reduce their occurrence. First, practice crop rotation and plant tomatoes in a different location from the previous season. Next, choose a resistant variety like Defiant. I also mulch my tomato plants with straw or shredded leaves to stop water from rain or irrigation from splashing spores onto the foliage. 

The last tip to preventing plant diseases is to put pruning to work. As the plants grow, remove the lower leaves to help stop or slow the spread of these diseases which first appear on the oldest leaves at the bottom of the plant. I also remove any blemished leaves that appear on the plants – those with yellowing or browning foliage. Use clean hand pruners to clip the leaves from the plant and add any diseased foliage to the garbage, not your home compost bin. 

5) Pruning when plants are wet 

This is a tomato pruning mistake we all need to remember! It’s a good general rule of thumb to avoid the vegetable garden after a rain or when the leaves are wet. Wet foliage can spread disease from leaf to leaf or plant to plant. To avoid stressing the plants, I aim to prune on a dry day in the morning or late afternoon.

6) Not staying on top of pruning

Tomato pruning doesn’t need to take up a lot of your time. I grow 50 to 60 tomato plants each year but spend less than 30 minutes a week pruning my plants. Staying on top of regular sucker removal makes pruning quick and easy. I use my fingers to snap off the sideshoots when they’re just an inch or two long. If you’ve neglected pruning for a few weeks and sucker growth has gotten out of hand you may want to retake control of your tomato plants with Missouri pruning. 

Missouri pruning is a technique that aims to curb overvigorous growth without stressing the plant. It’s used when suckers have grown too large to pinch all the way back to the main stem. Removing a large number of overgrown suckers could shock the plant or leave ripening fruits exposed to sunscald. To Missouri prune plants, use hand pruners to clip the growing tip of suckers back to two sets of leaves.

7) Neglecting end of growing season pruning 

A late season tomato pruning is a smart way to ripen up the last fruits on the plants. About a month before the first expected frost top the plants by removing all the growing tips. Cut back to clusters of fruits that likely still have time to mature. It’s tough love, but directs the sugars in the plants from new shoot production into fruit ripening. Suckers will continue to sprout after you top the plants so check them weekly and pinch out any new growth tips. 

8) Not cleaning pruning tools between plants is a major tomato pruning mistake

One of the most common tomato pruning mistakes is not cleaning the pruners or garden shears between plants. Using the same pruning tools to maintain all your tomato plants is asking for trouble. If one of your plants has been affiliated with a plant disease you risk spreading it to all of your plants. Instead, keep your gardening tools clean and sanitized by wiping the blades between plants with rubbing alcohol which contains 70% isopropyl alcohol. 

9) Over-pruning and exposing fruits to sunscald

In an effort to speed up ripening you may think it’s a good idea to clip out all the leaves surrounding the green tomatoes on your plant. However, over-pruning tomato plants can lead to sunscald. Sunscald occurs when developing fruits are exposed to full sun. This condition presents as pale patches on the fruits with those whitish areas eventually rotting. The best way to prevent sunscald is to be mindful when pruning tomato plants. Don’t remove all of the leaves that surround and shade the fruits. 

Learn more about growing awesome tomatoes in these in-depth articles:

• When to harvest tomatoes
• When and how to water tomato plants
• 22 science-based tomato companion plants
• Tomato growing secrets

Do you have any tomato pruning mistakes to add to our list?