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Indeterminate tomato plants grow much taller than determinate tomato plants. They are a vining plant that will continue to grow and produce fruit until they experience their first frost.
Therefore it is a good idea to provide them adequate support and to prune them to keep them healthy. To see how I support my tomato plants, please see my article Simple DIY Tomato Support System.
Determinate tomato plants on the other hand, are not a vining plant that continually produces fruit. They grow one large crop of fruit that all ripens at the same time, and then the plant dies back. This type of tomato does not need to be pruned as much. However, I would still prune around the base of the plant (see below for more on that).
There are a couple of good reasons why you should prune your indeterminate tomato plants to keep them healthy.
More than likely, your plants will still produce tomatoes if you choose not to prune. However, disease may set in earlier than if you don’t.
Once disease sets in, your plant will go into fight and flight mode, instead of staying in production mode. So you likely won’t get much more fruit from a plant, once it is diseased. Your best bet in fighting disease, is to spray on a fungicide, but at best, it will slow down the disease, not cure it.
And once one of your plants is ill, look out, as it will spread rapidly from plant to plant. A good thing to think about when planning your garden out, is to maybe not have all your tomatoes in one location. I have tomatoes in 3 different places in my yard, for this reason.
I live in the PNW, where we already have a cool, damp climate. Both of these things are bad for tomatoes who like it HOT and don’t like to be wet. So in my growing conditions, I feel like pruning the tomatoes really helps prolong my harvest for an already very short growing period.
If you really aren’t keen on pruning, might I suggest that you at least prune the bottom 12″-18″. I think anyone who gets rain, or waters their tomato plants, will benefit from this step. Which I do believe is most everyone!
I literally remove not only the stems and leaves from the dirt upwards to about 18″, but I also remove any long hanging leaves that might come from higher up and enter that zone. You basically want to eliminate any surface area for ground splatter to hit.
I will either take my thumb and forefinger and pinch off the branches near the main stem, or my absolute favorite pruners for the job, these little Friskars Micro Tip Pruners, they can get in to tough places super easily. Be sure to disinfect your scissors or pruners before using them to limit any spreading of disease, or spray them with some rubbing alcohol.
Do you ever get tiny holes in your plants leaves? These are often caused by flea beetles. They lay eggs in the soil and then jump up onto the foliage. Keeping the bottom of your tomato plant pruned, can also help prevent some damage from flea beetles.
When I do get a bad infestation of flea beetles, I like to sprinkle Food Grade Diaotamaceous Earth (aka DE) on top of the dry soil beneath the tomato plant. DE is a powdered mix of fossilized prehistoric crustaceans, which have very sharp edges. These sharp edges cut into the flea beetles, or insects in general, and they die.
Not sure what a sucker is? A sucker is another branch, that forms in the crook of an existing branch off of the main stem.
Pruning suckers is less critical in my opinion, than pruning the bottom area. I do try to prune most suckers off early in the season when I am pruning the bottom of the plant hard for the first time. Later in the season, I am less critical.
Later in the season, the only time I will prune off a sucker, is if it is on the front of the plant, leaning hard away from my support system. If I find that it is difficult to tie it to the support system, or it is leaning out causing a tripping hazard, I take it out.
Or sometimes the plant will just have too many suckers, and not have good airflow. Then I trim them out.
Rooting suckers in water, is a simple way to multiply your tomato plants quickly and cheaply. See my article Free Tomato Plants from Cuttings for more information on how to do this.
After you have chosen a few suckers to root, it is best to destroy the remainder of the cuttings. If there are any fungus or disease spores on them, you do not want that in your compost. I always throw mine in our firepit, or you can bag them up and throw them in the trash.
Still not sure what to prune? Here is a step by step pictorial:
Be careful not to cut off so much foliage, that your tomato fruit is exposed to the sun. If the fruit is exposed to the sun it will get sun scald. Sometimes for this reason, you must leave a leaf or branch in place, if you have very low growing fruit.