How to prune tomato plants

Tomato plants don’t naturally want to grow the way we are accustomed to growing them. Left to their own devices, tomato plants will become a giant sprawling tangle of branches, leaves, and fruit. We tend to grow them in tomato cages or set up some kind of trellising device for more convenient harvesting, conserving garden space, and ultimately healthier plants. To achieve all of this, you will likely need to prune your tomato plants.

To prune or not to prune

There are some gardeners who do not prune their tomato plants, and if that gives you the results you are looking for, then by all means, let them grow wild! I will get to all of my reasoning for why I prune my tomatoes, but there are a couple of reasons you may choose not to.

First, you need to be aware of what kind of variety of tomato you are growing, and whether it is a determinate or indeterminate variety. This should be noted on your seed packet or plant tag if you bought a started tomato plant. If you know the variety name, a quick Google search should point you in the right direction.

A determinate tomato plant has a set, pre-determined height that it will grow to and a certain amount of fruit that it will set. Determinate varieties set almost all of their fruit at once. They are much smaller and grow in a more compact, bush-like habit.

My determinate Martino’s Roma tomatoes, which I let grow wild and un-pruned

An indeterminate variety, on the other hand, will continue growing and producing fruit as long as the plant is healthy and the weather allows it to do so. These plants can get HUGE if the growing conditions are right.

An indeterminate, yellow pear tomato plant, pruned to a single stem.

As a general rule, only indeterminate plants should need pruning. If you prune your determinate plants, which will only set a certain amount of fruit, you will cut down on your harvest significantly. So I would not recommend that you prune any of your determinate varieties.

If you have ample growing space and like a more low maintenance, wild garden, then you might choose not to prune. If you are able to space your tomatoes two or three feet apart and let them thrive and set as much fruit on as many branches as they want, then go for it! Air-flow and backsplash may still be issues you’ll want to consider avoiding, but it can definitely work.

Reasons to prune

Here are a few reasons you may choose to prune your indeterminate tomato varieties:

  • it keeps plants more compact and manageable
  • it promotes air circulation, which is especially important in wet or humid conditions
  • it makes it easier to stake, cage, or otherwise support your plants
  • it can maximize fruit production
  • it can minimize risk of disease
  • it can allow you to grow more plants in a smaller space
  • harvesting is more convenient

I choose to prune my tomato plants because I am growing in raised beds in a limited space, so I want to be able to grow as many plants as possible, keep my plants healthy for as long as possible, and thus increase my harvests.

How to prune tomatoes

Start with clean, sharp garden snips, pruners, or scissors.

First, remove any lower branches that are touching the soil. Most diseases that affect tomato plants come from the soil, and from water splashing soil onto lower leaves, so it is important to keep the lower stem clear of leaves. As the plant grows, you can remove more and more lower leaves, but when the plant is young, be sure not to remove too many. A good rule of thumb when pruning any plant is to never remove more than 2/3 of a plant’s foliage at one time. The plant needs those leaves to photosynthesize, so avoid doing a hard prune when the plant is very young and small.

Next, move up the main stem of the tomato plant and identify and remove all “suckers.” A sucker is an off-shoot that grows in between the main branch and a leaf. It grows in what looks like the “armpit” of the plant. If the suckers are small, you can simply pinch them off. Otherwise, use your snips and cut each sucker off at the base, being careful not to cut the branch or main stem.

Before pruning
After pruning

If left alone, a sucker will continue to grow and eventually split off into a second main stem. I usually try to keep my tomato plants pruned to one main leader stem. However, if there is a sucker that is really established when I come to prune it, I will sometimes make an exception and keep to a two stemmed plant. It can sometimes be hard to distinguish the main stem from an established sucker, and you definitely do NOT want to cut the top off your tomato plant, as this will prevent your plant from growing any taller. Really, you can prune your plant to as many main stems as you see fit.

I hope this helps you keep your tomato plants under control and thriving this summer!

Until next time,

-Jourdin

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