Do tomato plants need to be pruned?
In my first years of gardening, it seemed everyone told me, “yes.” But as I gained more experience and began listening to other gardening experts, I learned that the answer to this question isn’t as clear as you’d think.
People get passionate about tomato pruning. But I started asking myself, “why?”
Is it because this is the way they’ve always done it? Because their mom or grandpa told them that’s the best way to care for tomatoes? Or are people pruning tomatoes (or not pruning) based on their own experience and tests?
It seemed everywhere I turned I received conflicting information, so I did what I encourage every gardener to do. I tested it in my own garden.The results were so clear to me that I’ll never look at pruning tomato plants the same way again.
In this episode of the Beginner’s Garden Podcast, I talk about pruning tomatoes — how to do it, the potential benefits and drawbacks, and finally the results of my own experiment of pruning vs. not pruning tomatoes in my garden. Click below to listen or continue reading.
What Does it Mean to Prune Tomatoes?
When your tomato plants are growing, they have one main stem (sometimes two) growing up and lateral stems growing to the side. In the junction between these you’ll find a shoot often called a “sucker.” A sucker begins very small. But if left alone it grows into its own main stem that produces lateral stems and more suckers.
Which Tomatoes Do Not Need Pruning?
When we talk about pruning, we are talking about indeterminate tomatoes. Indeterminate tomatoes keep growing all season unless they are killed by frost or disease. Determinate tomato plants — like Roma tomatoes — produce all of their fruit in a big burst and then stop.
(You can learn more about these two types in my post about growing a salsa garden or my post about tomato trellis options for both determinate and indeterminate varieties. To find out which tomato plant you have, check the plant tag or seed packet.)
Regardless of whether you decide to prune suckers off your tomato plants, you won’t need to prune Roma or other varieties of determinate tomatoes. If you do, you will limit your harvest. For the rest of this discussion, we’ll talk about pruning indeterminate tomatoes.
Potential Benefits of Pruning Tomatoes
Prevention of fungal disease. Most people agree that pruning your tomato plants can help prevent diseases, specifically fungal diseases like early blight or septoria leaf spot. These diseases are characterized by yellow leaves at the bottom of your tomato plant. You can learn more about that here. In general, good air flow inhibits the spread of fungal diseases, and pruning can help open up the plant and increase airflow.
Tidy tomato plants. Pruning also keeps the garden area tidy. If you don’t prune your indeterminate tomatoes, they can get out of control. This can lead to difficulty in caring for the tomatoes and harvesting them. In some cases, tomatoes left on their own show signs of less overall plant health.
More sunlight on leaves. Another possible benefit of pruning is to keep enough sun on the tomato leaves. The thought is, lower leaves are unable to get the sunlight required for photosynthesis.
Larger tomatoes. If you do prune tomatoes, the plant will produce fewer flowers because of fewer suckers. Fewer flowers means fewer tomatoes. On the other hand, if your plant produces fewer tomatoes, the fruit may grow larger. In fact, a Purdue study found that there was a 25% increase in fruit size when the suckers are pruned.
Conflicting Opinions on Benefits of Pruning Tomato Plants
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Does sunlight ripen tomatoes? If you research whether you should prune tomatoes, you’ll find many opinions stating that the fruit will ripen faster because they have more sun.
But tomato growing expert Craig Lehoullier, author of my favorite tomato growing book, Epic Tomatoes, says that this is not true. He contends that shade produced by unpruned vines will not affect the ripening of the fruit.
However, I’ve observed that the gardeners who talk about this benefit live in cooler, rainier climates with less sun. It stands to reason they have a bigger problem with the shade.
Personally, when I prune my tomatoes in my hot and sunny Southern climate, sunscald is a huge problem because my tomatoes aren’t getting enough shade. Ultimately, you may need to think about your climate when deciding whether to prune or not.
Does pruning tomato plants shift sugar production from leaves to fruit? Another debated benefit is that energy, specifically sugar, goes to the growing fruit, not the foliage, when you prune. Others will say that it’s the foliage that makes the sugar so if you have more foliage you’ll have more sugar for the extra fruit. This is one question you’ll find multiple answers to and is best tested in your own garden.
Drawbacks of Pruning Tomato Plants
Disease pathway. When you remove the sucker, it opens a wound, which can become a pathway for diseases or insects. I’ve never noticed this in my garden, but I can see how it could be a problem. Pinching the suckers when they are small would limit the size of this wound.
Limiting photosynthesis. If the leaves produce sugar for the plant and the fruit, then with pruning, the plant loses some ability to produce that sugar.
Sunscald. Leaves shade the fruit, which helps to prevent sunscald. This is especially helpful if you live in a hot climate.
Less yield. I mentioned the Purdue study earlier that found pruned tomato plants produced fruit 25% larger than unpruned. The flip side of that study is that there was a 38% more yield in pounds from the unpruned plants. The thought is, then, if you prune your tomatoes you should get bigger fruit but if you don’t prune you’ll get more but smaller tomatoes.
Time commitment. The biggest drawback to pruning tomatoes for me is the time commitment. Depending on how many tomato plants you grow, this could be a significant time commitment to prune once a week.
Topping Tomato Plants When They Grow Too Tall
Toward the end of the gardening season, whether you choose to prune the suckers from your tomato plants or not, you may ask, “How do you keep tomato plants from growing too tall?”
You can top off your plant, which means to cut the tip of the main stem at the top of the plant. Then, the plant will use its energy to produce and ripen fruit and keep the plant healthy. This also helps keep your garden tidy and prevents your plant from toppling over, especially if you don’t have a trellis method in place to handle this tall growth. (Here are other ways to stake your plants to prevent toppling over that I’ve used successfully).
Experts recommend topping off your plants about 30 days before your average first frost in the fall. This will help direct energy toward ripening your last tomatoes.
Pruning Vs. Not Pruning: My Experiment
I want to encourage you to do your own experiment! Grow a couple of tomatoes you prune and a couple you don’t and see what works best in your own garden. Your results may very well depend on your climate, what varieties you grow, and many other variables. You should see what is best in your garden.
For my experiment, I grew two rows of indeterminate tomatoes side-by-side and staked them using my PVC/Rebar trellis method. I grew Black Krim, Arkansas Traveler, and Amish Paste varieties, and I pruned one and did not prune the other. As the harvest season progressed, I kept track of my harvest from each row — I tracked yield, approximate size of the fruit, and disease resistance.
I found that my unpruned row produced 37% more yield by the pound than my pruned row. I did not see any difference in size of the tomatoes between my pruned and unpruned row, either.
In addition, one benefit of pruning is supposed to be to have healthier plants but I did not find that in my garden. Both the pruned and unpruned rows were ruined by Septoria Leaf Spot equally.
(Interestingly, in a tomato planting in the other side of the garden, where the plants were spaced further apart in heavy duty tomato cages, but still left unpruned, I harvested tomatoes several weeks longer before they also succumbed to the disease.)
Should YOU Prune Your Tomato Plants?
Although the results of my experiment have led me to stop or at least limit the pruning I do on my own tomato plants, I do not necessarily believe my method is right for everyone. I hope you’ll test it in your garden like I did. But if you aren’t in the mood to conduct a science experiment, here are some questions that will help you make an educated decision for your garden this year.
How much garden space do you have? If you have less space, you might consider pruning more.
What kind of tomato support or staking will you use? Strong cages allow less pruning, while single-stem staking methods require it.
What is your climate like? If you’re in a hot, humid climate, less pruning will give ripening fruit more resistance to sunscald.
As you can see, we all will have slightly different variables in our gardens.
If you’ve ever tested pruning vs. not pruning tomatoes, what have you found? Comment below!
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