A Practical Guide to Pruning Your Tomato Plants

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If you’re new to growing tomatoes, you’ll quickly find out there’s some conflicting ideas on how you should be pruning your plants. You’ll probably be guessing on when, how, and how much to prune. Should you pinch all the “suckers?” Does pruning (or not pruning) affect the size of your harvest?

Like most things involved in a garden, the best way to prune your tomato plants depends on what you’re working with. Tomato variety, climate, and the type of support or trellis system you’re using all come into play. As long as you understand the basics of how pruning affects your plants’ growth, you really can’t mess up.

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First Thing’s First: IDing Branches vs. Suckers

You’ll hear the term “sucker” mentioned a lot in the tomato pruning debate, so let’s clear up what a sucker actually is.

Tomato plants have main branches, which are the foliage and flower clusters that grow directly from the central stem. Once the plant gets a bit bigger, it’ll start to put out suckers, which are little shoots that pop in between the main stem and the branches. In the tomato plant’s “armpits,” if you will.

“Sucker” is a sort of a misnomer when we’re talking about tomatoes. With fruit trees, unwanted shoots that spring up from the roots are called suckers because they suck energy away from the main tree. Tomato suckers are just part of the plant’s regular growth, though. All tomato plants produce them, and they’ll become strong new stems that will bear tomatoes.

Some folks say you should remove ALL the tomato suckers, and some say you should only remove a few. To decide on a game plan for snipping suckers (or other foliage, for that matter), the first thing to know is whether you’re growing determinate or indeterminate tomatoes.

Determinate vs. Indeterminate Tomatoes

The majority of tomato plants are indeterminate, including all your heirloom/open-pollinated varieties and many hybrid tomatoes. Indeterminate tomatoes have a vining growth habit. They’ll continue to grow, produce new flower clusters, and set more fruit until frost or disease takes them down. These plants can grow 8-10 feet tall, and their big sprawling vines get quickly out of control without a little pruning and training.   

Determinate tomatoes are a smaller group of hybrid varieties that grow to a certain height (usually 4 to 5 feet) and ripen all their fruit within a few weeks. These varieties grow like a bush instead of sending out long vines, making them easier to manage.

For maintenance, all determinate tomato plants need is some support so they don’t lean from the weight of the fruit. They don’t require any real pruning, and getting too snip-happy will slash your harvest. Unlike the indeterminate varieties, determinate tomato plants will only produce a set number of flowers (would-be tomatoes). Once they’re done, they’re done. That means every sucker or growing point you cut off will cost you fruit the plant won’t replace.

If your determinate tomato plants’ lowest leaves are close to or touching the ground, it’s okay to prune those away to keep the plants clean. Otherwise, leave those babies alone. 

Why do indeterminate tomatoes need pruning?

Our modern ‘maters are bred to do some unnatural things. For example, producing giant fruit their wild ancestors would’ve deemed impractical. If the vines are allowed to sprawl around as they please, they’ll either break from the weight of that fruit or end up lying on the ground. You don’t want tomato vines on the ground, since they’re extremely prone to soil-borne diseases.

In order to protect your tomato plants from themselves, you’ll need to train the vines with a trellis or other support method. Think a cattle panel, trellis netting, stakes and twine, or whatever creative solution you can come up with.

Whatever route you go, the aim of pruning is to keep your tomato plants confined to their support structure without allowing the vines to get too crowded. Tomato vines don’t climb like other vining plants do, so you’ll have to tie or clip them in place. It’s usually necessary to remove excess foliage or vines that won’t cooperate to keep things nice and neat.

Should you remove all the suckers?

The practice of removing all the tomato suckers as they pop up is known as the single stem method. Greenhouse growers and commercial farms often use this method for high-intensity growing, and it’s gotten pretty popular among backyard gardeners, too. You’ll hear this advice so often you might think it’s the ONLY way to do it.

Allegedly, suckers steal energy from the fruit, and removing them results in bigger tomatoes. Again, though, suckers are just additional fruit-bearing branches on the plant. They’re not secondary “parasite” plants like your typical root suckers. While it’s true that allowing a tomato plant to fruit as much as it wants to means some of those fruits will be smaller, there are some drawbacks to growing on a single stem.

Pros and Cons of the Single Stem Method

The single stem method works fine, as long as growing conditions are completely optimized. If you’re lucky enough to have perfect soil, no pests, and ideal weather for tomato plants, it’s a great way to maximize space and reduce maintenance. Plants grown on a single stem can be spaced much closer together, and they can be easily trained to a single stake or string. For many of us, though, growing this way creates a liability for our plants.

Here are a few potential problems with using the single stem method:

Less foliage can lead to sunscald on fruit.

If you’re getting scorching hot weather by the time your tomatoes are ripening on the vine, having too-sparse foliage may expose the fruit to too much sun. Sunscald can cause ugly blemishes on your tomatoes, which can open the door for secondary rot. A full canopy with multiple branches provides plenty of shade to prevent this trouble.

Plants may be worse affected by disease.

In areas that see hot weather, high humidity, and regular thunderstorms during the summer, tomato plants tend to catch leaf diseases like early blight and septoria leaf spot. These diseases are all but unavoidable in this kind of climate, and they’ll steadily defoliate plants from the bottom leaves up.

Pruning for cleanliness and airflow helps delay the spread of blight, but having too little foliage makes it harder for plants to fight back when blight inevitably shows up. That’s because the leaves supply much of the energy they need to grow. Heavily pruned plants without extra branches may run out of steam, when that lower foliage starts to decline. If the plants can’t “outrun” the blight by putting on healthy new growth, they’ll stop producing tomatoes and eventually die.

Pest damage has a bigger impact.

Pests are also more likely to hammer your tomato plants’ leaves during hot weather. If you’ve seen hornworms in action, you know how quickly they can strip tomato foliage. A few hungry hornworms gone unnoticed can mean game over in no time, if your plants don’t have many extra leaves to spare.

In short, your plants need to be in mint condition to grow tomatoes with as little foliage as possible. Anything that affects leaf health, whether pests, disease, or nutrient deficiency, will cause bigger problems for fruit quality and production if there’s less foliage to pick up the slack.

I’ve tried using the single stem method here in our north Georgia climate, and those plants were horribly affected by blossom end rot. They also succumbed to early blight a full month earlier than we’d usually expect for that particular heirloom variety. We barely got 2 lbs of usable tomatoes off each plant. Never again!

Does letting suckers grow really lead to smaller fruit?

It’s certainly true that the suckers themselves produce smaller tomatoes. The biggest tomatoes are usually those produced from the main stem. And sure, you might could force the plant to put a bit more energy into those main fruit clusters by removing the suckers. Remember, though, that’s if you don’t have any problems.

For many of us backyard gardeners, a slight difference in fruit size really isn’t worth the risk of stripping tomato plants of all potential branches. Tomatoes that are allowed to branch out some will still produce lots of healthy, good-sized tomatoes.

Pruning Tomatoes for Cleanliness, Stability, and Airflow

For growing tomatoes out in the elements in your backyard garden, you’ll get good results when you focus on pruning to support your plants’ health instead of manipulating fruit size. Below are some ways to do that:

Prune branches that are touching (or close to) the ground.

Since tomatoes are vulnerable to soil pathogens, it’s a good idea to make a little space between the lowest leaves and the soil. Snip those lowest “sun leaves” that tend to lay on the ground, plus any that are close enough to get a lot of splash-back during heavy rains. Ideally, work your way towards having a foot or so between the ground and the foliage, by the time your plants are large and setting fruit. 

Thin out dense areas where leaves are crammed together.

You don’t want your tomato patch to become an impenetrable thicket, since sunlight and airflow help prevent the spread of fungal diseases. If you see an area where the leaves are really crammed, snip a few to let some light in. 

Remove “rogue” suckers that won’t cooperate with your trellis or support.

It’s important to make sure all your plants’ branches are well-supported. Sometimes, you’ll have suckers that just aren’t going to work with you. For example, if you’re using some trellis netting and you get a sucker growing out in the complete wrong direction, remove that one so you can keep the plant neatly confined to the trellis.

Prune or pinch suckers that develop higher on the main vine.

Allowing suckers to grow into thick branches too high up can make your plant top heavy and hard to deal with, especially with varieties that produce big tomatoes. Suckers that grow up high are typically weaker and produce smaller fruit, as well.

I like to start pinching suckers that develop near the top once the plants are around three to four feet tall, depending on the variety. As you get experience growing different tomato varieties, you’ll get a feel for how the suckers behave and how many/which ones to remove.

When should you start pruning your tomato plants?

There’s no hard and fast rule, here. Once your plants have established and hit their first growth spurt, watch them and prune as needed to keep them well-supported. It’s always better to prune a little at a time as they grow, rather than waiting until you’ve got a bunch of thick, unruly branches that need cut all at once. You can supposedly prune up to one third of the foliage in one whack without stressing your plants, but this can vary depending on the plants’ age and health.

As a beginner, one of the best ways to build your tomato-pruning skills is to get familiar with how tomato plants grow. With your first plants, prune lightly and focus mostly on keeping foliage and vines off the ground. Let those plants go a little, so you can watch how the suckers and main branches develop as the plants mature. No pressure, you’ll still get great tomatoes with minimal pruning.

You’ll find that different tomato varieties have different pruning needs. Some are just better behaved than others, and those that produce smaller tomatoes can support a lot more branches and fruit without trouble. For example, lots of cherry and plum types can produce good fruit even on the higher suckers. With the right trellis, you can mostly just let them do their thing.

Pruning Diseased Foliage

A lot of sources maintain that removing blighted foliage is an essential part of the “treatment plan” for diseased tomato plants. But there are a few factors to consider before you start madly hacking away any branch that has a spotty leaf.

Once you see signs of fungal leaf spot such as early blight on your plants, there’s no getting rid of it completely (especially if you’re growing all naturally). The symptoms mean disease spores are present and conditions are right for the fungi. Even if you cut off every affected leaf, new spots will turn up elsewhere before long. The only thing you can do is try to slow the spread and reduce the impact on your harvest.

For early signs of disease, pruning a few blighted leaves here and there won’t hurt. It might help reduce the spore count. Be careful not to overdo it, though, if quite a few leaves already have spots. Pruning too much can stress the plant. Plants have immune systems just like people, and stress lowers their ability to resist disease pressure.

I’ve had bad outcomes from heavily pruning plants with early blight and septoria leaf spot, even following that “one-third” rule. This is probably because a plant that’s already under attack has a lower stress threshold.

If you see a lot of diseased foliage on your tomato plant(s), only remove the worst affected leaves. I.e., any that are yellowed, withering, and are clearly no longer doing anything for the plant. Then, focus on “supportive care.” Give the plants some gentle, water-soluble fertilizer such as fish emulsion to help bolster their defenses and encourage new growth. A lot of the time, healthy tomato plants will outpace fungal disease and still produce a good harvest.    

Read this post for more about keeping your tomato plants in top shape: Tomato Plant Care: 9 Steps for Healthier Plants and Bigger, Better Yields.

Some Best Practices for Pruning

Here are a few guidelines to keep your tomato plants happy and thriving after you give them a trim:

Get those suckers while they’re small.

Tomato suckers get big pretty fast. If you get them while they’re still tiny, you don’t even need to break out the shears. Just pinch off the ones you’re not keeping with your fingers. This is easier on the plant, too, since cutting off large, thick branches creates bigger wounds and thus bigger opportunities for disease to enter.  

Go easy when pruning younger tomato plants.

Smaller tomato plants, especially those that haven’t established yet or have just started to, are way more susceptible to stress from over-pruning. Also, the leaves provide energy, and your little plants need all the energy they can get to grow.

At this point in the game, don’t worry too much about leaves being close to the ground. Tomato plants aren’t nearly as prone to disease at this age, especially in the spring when the weather is still mild (though it’s always good to have some mulch around your plants to prevent lots of splash-back).

The lowest, oldest leaves on young tomato plants will often curl, yellow, or start to look generally sad during their first few weeks in the garden. This is caused by normal transplant stress, and it’s fine to remove the sad leaves. Just wait until the plants are several feet tall and actively growing before you start snipping healthy foliage. 

Try not to prune during or before wet weather.

Remember that pruning tomato foliage creates an open wound in the plant tissue. Since fungal and bacterial diseases are favored by damp conditions, prune during dry weather so the cuts can heal over before your plants get a drenching. Freshly cut stems that get wet may open the door to bacterial wilt or fungal stem canker. No need to worry, if an unexpected afternoon shower pops up after you’ve pruned. It’s just a good rule of thumb to keep in mind.

Don’t prune much when it’s hot out.

Pruning more than a couple leaves on a hot afternoon can stress tomato plants, causing shock and leaf curl. It’s best to wait til evening on hot days, if you plan to give your plants a decent trimming.

Pruning tomatoes is one of those low-stress garden chores you can learn as you go along. The only real mistakes to be made are removing way too much at once or over-pruning determinate plants. As you spend time maintaining your tomatoes, you’ll figure out what approach works best for your setup and the varieties you like to grow.