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7 Tomato Pruning Mistakes to Avoid

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Getting ready to prune your tomato plants? Before you dig out the clippers, be aware of the top tomato pruning mistakes to avoid.

This way, your cuts and snips have the best chance of accomplishing pruning’s goal: more tomatoes, bigger tomatoes, and healthier plants.  

Avoid these tomato pruning mistakes for a healthier crop

Tomato pruning mistake #1: postponing pruning 

When should you begin pruning your tomato plants? Sooner than you think – once plants are between 1-2 feet tall. You want to avoid stems and leaves drooping onto the soil, because they will pick up microbes that can infect them in their earliest days and weeks.

That’s why it’s smart to be on the lookout for simple pruning opportunities from the start of the season. Keep a vigilant eye on side stems that grow directly off the main stem of a tomato plant. When a hopeful sucker appears in between the main stem and side stem (in the “crotch”), consider clipping it. If you let a sucker grow, it will become a full-blown stem and develop its own blossoms. Extra stems divert energy from the main plant’s fruit production. When you prune suckers, plants invest less energy in producing extra branches and leaves and more energy in fruit, producing an earlier crop.

Tomato pruning mistake #2: pruning determinate tomato plants

Delegate tomato pruning to indeterminate tomato varieties only. This saves you time. But there’s another, practical reason to do so.

Determinate tomatoes have automatic pruning built into their systems. They grow to a certain height and then stop. Because of that, these types of tomatoes produce fruit for a few weeks and then production fades out. Do you want to limit them? I think not.  Pruning determinate tomatoes means you throw away potential branches, blossoms, and fruit.

The exception is the suckers that form below the first flower cluster. When you prune a sucker below a determinate’s first flower cluster, you won’t affect the plant’s crop … blossoms and fruit won’t form there anyway.

Tomato pruning mistake #3: pruning when the plants are wet

Pruning a tomato is like opening a vein. All kinds of stuff can go in and out. That includes fungi, bacteria, and other nasty microbes from which you want to protect your tomato plant. Water transports those microorganisms. Even a few stray droplets can open up your plants to infections. Wait until your plant is completely dry before you prune. 

Tomato pruning mistake #4:  pruning with dull or dirty tools

It’s for the same reason – to avoid spreading diseases – that you should disinfect your garden clippers or knife before pruning tomato plants. Dampen a cloth with a 10% bleach solution and wipe the edges carefully. While you’re at it, check to ensure that the edges are sharp to you can make clean cuts and avoid injury to plants.

Speaking of tools, try using bypass clippers (versus loppers or shears) to prune tomatoes. They are designed to work in tight spaces.

Tomato pruning mistake #5: pruning midday or in heat

The best times of day to prune tomato plants are early in the morning or in the evening when temperatures are cooler. If you prune midday – or during a heat spell – you add unneeded stress to your tomato plant. Think of it: some of your plant’s limbs are being cut away. Don’t make it any harder on the plant than necessary.

Tomato pruning mistake #6: over pruning

If you get too scissors-happy, your plants will suffer. Meaning they may not overcome the shock of losing a good portion of their photosynthesis machine.

Over pruning tomatoes opens the inside of the plant to excessive sunlight. Fewer leaves mean less shade for fruits, which is especially dicey when temperatures and humidity are high. At best, an over pruned tomato plant may produce fruits with sunscald. At worst, it may struggle to survive.

Good rule of thumb: cut away less than a quarter or third of a plant at a time – at most. Leave plenty of branches to shade fruit during hot spells.

Tomato pruning mistake #7: avoiding late pruning

Fall is closing in. Maybe it’s already here. You don’t want to face the fact that tomato growing season is over. Here is where you – like so many other gardeners – make one of the biggest tomato pruning mistakes. You stop pruning suckers. And you leave the tomato plant’s main stem intact rather than lopping it off. 

Doing so means your plant continues to invest all kinds of energy into pushing out new branches, leaves, flowers, and fruit. Meanwhile, the fruit already on the vine continues to fight for energy to mature and ripen. 

Avoid this struggle. Help your existing fruit finish triumphantly. Keep after the suckers that pop out in between the main stem and its branches. While you’re at it, look for excess leafing branches with no fruit and give them a trim, too. Doing so will allow more sunlight to reach the green tomatoes already on the vine.

And be brave. Go ahead and prune off that main stem at the top of your plant. It’s called “topping” your tomatoes. Time this final pruning chore to about 30 days before your area's last projected frost.

Doing so will allow the plant’s resources to pour into ripening the green tomatoes already on the vine. You’ll have luscious globes of red fruit. And you’ll have a head start in tidying up your garden before winter.

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