The Ultimate Guide: Why and How To Prune Tomato Plants

Tomato plants, a staple in many gardens, can greatly benefit from the art and science of pruning. Proper pruning not only shapes the plant but also enhances its productivity and health.

As growers aim for a bountiful and robust harvest, understanding the nuances of pruning becomes crucial.

Published: September 20, 2023.

Pruning tomato plants can help improve the health of the plant, increase fruit size, and yield a more bountiful harvest.

Here's a step-by-step guide on how to prune tomato plants and the reasons behind it.

Why Prune Tomato Plants?

Pruning is just a part of taking care of tomatoes, but it should not be neglected. Pruning is often combined with stalking and supporting tomato plants, ensuring that they grow with ample of air and sun around the plants. Also, regular pruning ensures:

• Air Circulation: Removing some of the leaves and branches improves air circulation, which reduces the risks of fungal diseases.
• Improved Sunlight: Pruned plants allow more sunlight to reach the fruits, which can improve ripening.
• Energy Distribution: By removing unproductive stems and leaves, the plant can direct more energy into fruit production.
• Support: Tomato plants, especially indeterminate varieties, can become top-heavy. Pruning helps reduce weight and makes them easier to support.
• Larger Fruit: Pruning can result in larger but fewer fruits, which might be desirable for some gardeners.

When Should You Prune Tomatoes?

It's best to prune tomato plants in the early morning when the plants are dry.

If they're damp from rainfall, dew, or irrigation, allow them some time to dry off.

Start pruning when the suckers reach a length of two to four inches. This prevents the plant from directing energy to grow branches away from the primary stems.

Indeterminate tomato varieties should be pruned every few weeks since they keep growing throughout the season or whenever you are in the garden working with your tomato plants.

How to Prune Tomato Plants

There are primarily two types of tomato plants, determinate and indeterminate tomato varieties, which are pruned in different ways:

• Determinate: These plants grow to a certain height and then stop, with all the fruits maturing around the same time. They typically require less pruning and most of the gardeners simply remove dead or ill leaves and branches.
• Indeterminate: These plants continue to grow and produce fruit until killed by frost. They benefit the most from regular pruning.

When pruning tomatoes, it is important to remove everything that is dead or ill.

Also, it is important to identify and remove suckers - the suckers are the small shoots that grow out from the joint where a branch meets the stem.

If left to grow, they can become large stems with blossoms and fruit, but they can divert energy from the main stems.

Pruning Process

• Using clean and sharp pruning shears or your fingers, pinch off the suckers when they are young and small (about 2-4 inches long). For larger suckers, use shears to avoid injuring the plant.
• Start at the bottom of the plant. Remove any leaves or branches that touch the ground, as these can be entry points for disease.
• Remove yellow or diseased-looking leaves, as they will no longer benefit the plant and can be a source of disease.
• For indeterminate varieties, some gardeners like to prune the plant to one or two main stems to increase the size of the fruit and make the plant easier to manage. If you choose this method, consistently remove the larger suckers and only keep the desired number of main stems.

During pruning, there are several more tasks a gardener should do:

• Staking and Supporting: Once pruned, ensure your tomato plant is well-supported using stakes, cages, or trellises. This helps keep the plant off the ground, further reducing the risk of disease and making harvesting easier.
• Regular Maintenance: Check your tomato plants weekly and remove any unwanted growth or diseased areas.
• Be Gentle: While pruning is beneficial, too much can stress the plant. Always use clean tools and make clean cuts.

Some "experts" claim that it's not essential to prune tomato plants because many gardeners grow healthy and productive plants without much pruning.

However, a properly pruned indeterminate tomato plant is healthier and stronger, and although in theory, it doesn't bear the largest number of fruits, the fruits are healthier, larger, and often tastier.

The key is monitoring your plants, understanding their needs, and determining the best approach for your garden and gardening goals.

Common Tomato Pruning Mistakes to Avoid

Pruning is essential for the health and productivity of tomato plants, but it's crucial to do it right.

Ensuring you prune at the right time and manner will safeguard your plant and its harvest. Here's what you should avoid when it comes to tomato pruning:

Over-pruning determinate tomato varieties

Determinate tomatoes have a fixed growth pattern set in their genes, which includes a specific number of stems, leaves, and flowers.

During their growth cycle, they form most of their leaves and stems, leading to a distinct pattern. After flowering and achieving their full leaf span, they don't grow further.

Thus, for determinate tomatoes, only remove the suckers below the first flower cluster. Pruning above this cluster might result in fewer fruits. Though not all tomatoes are determinate, those that are tend to be more compact and need less support.

Of course, remove anything that looks ill or dead. If the plant is too dense, remove a few leaves/branches and let air and sun in, but don't overdo it.

Using blunt or unclean tools

Garden clippers, commonly known as pruners, are ideal for tomato plants.

These hand-operated tools are adept at cutting stems up to an inch thick. Over time, they can accumulate dirt, sap, moisture, and other debris, leading them to dullness or rust.

These conditions not only hamper their performance but can also transfer diseases between plants. To maintain them, lubricate the blades to prevent rust and ensure smooth operation.

Regularly sharpen the blades using a knife sharpener or consider blade replacement for a precise cut. Blunt blades can harm the plant by crushing the stem instead of providing a neat cut.

Pruning during damp conditions

Trimming tomato plants when they're damp or during rainfall can increase the risk of disease, especially bacterial and fungal infections.

A key reason for pruning tomatoes is to enhance air circulation, which helps prevent fungal issues.

To further protect against moisture-related diseases, like tomato blight that results in rot, remove the bottom leaves of the plant that come in contact with the ground. This is especially vital in regions with heavy rainfall that makes the soil wet.

Excessive pruning

Pruning tomato plants excessively can strip away too many leaves that provide shade, leaving the fruit vulnerable to intense sunlight, leading to sun scald.

Taking away more than a third of the plant's foliage at once can not only damage the fruit but may also threaten the plant's life.

It's better to prune after the fruit-setting phase gently. This approach not only manages the plant size but also promotes new growth, fostering increased flowering and fruit production.

If the plants are too dense, remove excess leaves and branches during the period of a few weeks - this is a shock to the plants as well, but not as large as it would be if, for example, one-third of leaves and branches are removed.

Note: if the tomato plants have too much nitrogen, they will grow quickly and very tall. However, they will be weak and prone to diseases. If that happens, fertilize them in the future using slow-release balanced fertilizers with lower amounts of nitrogen and with organic fertilizers for tomatoes.

Delaying pruning of tomato plants

Procrastinating on pruning allows those tiny suckers to evolve into substantial, weighty branches. This extra weight can burden the plant and obstruct sunlight and air from reaching the plant's core.

For such mature branches, standard garden clippers might not suffice, and you may require loppers for effective pruning. It's simpler to prune when the suckers are still small. Remember, frequent checks and pruning are necessary as new suckers continually sprout.

Moreover, these matured suckers consume a significant amount of the plant’s energy, which could have otherwise been channeled toward yielding more and larger fruits.

If you have enough space and plants are strong enough, you can let your tomato plants grow 2-3 stems (three is really more than enough), not just one.

Neglecting to trim the primary stems as the growing season concludes

As the growing season draws to a close, trimming the growth tips can help divert the plant's sugars to the maturing fruit.

This is ideally done around 30 days before the anticipated first frost. This practice, known as “topping the plant,” entails cutting the end shoot just above the last flower set.

This technique aids in maximizing the yield of ripe tomatoes instead of ending up with mostly unripe green ones.

By doing so, you ensure that the nutrients, which would otherwise fuel new growth, support the ripening of the existing fruit, especially since new growth isn't crucial at this stage of the season.

However, if you are growing indeterminate tomatoes in containers on carts (with wheels) and you have indoor space with a large glass surface, you can avoid "topping the plant" - as soon as there is a danger of frost, take your tomatoes indoors and place them near the windows (don't let the leaves touch the glass).

If required, warm up the area and even add some artificial grow lights - growing tomatoes indoors is a little bit trickier than growing them outdoors, but indeterminate varieties can bear plenty of fruits even during winter.