Some controversy exists over whether or not tomato plants should be pruned, and the reality is that if you don't, it will not cause problems. Plenty of people do not prune at all and still grow good tomatoes. Tomatoes are not one of those plants that require pruning or deadheading in order to thrive, but shrewd pruning can improve the quality of the fruit you harvest.
Why Pruning Might Help
The main reason to prune tomato plants is that it helps your plant direct its energy toward producing fruit rather than producing more foliage. Unpruned foliage will eventually grow into new branches that will form fruit, but most experienced growers advise that tomatoes should be pruned to not only produce larger fruit earlier in the season but also to protect the plants against pest and disease problems.
When a tomato plant is pruned properly, all of the foliage receives adequate sunlight, and the plant is able to photosynthesize more efficiently, boosting growth and fruit production.
Determinate vs. Indeterminate Tomatoes
Not all types of tomatoes need to be pruned. If you are growing determinate tomatoes, you don't want to prune. Because determinate plants develop all of their fruit at one time, pruning may cause you to sacrifice tomatoes for no reason.
If you're growing indeterminate tomatoes, which produce fruit regularly over the course of a season, pruning is essential. This helps keep the commonly huge vines in control, and it encourages the plant to produce several large tomatoes instead of lots of foliage and many smaller tomatoes.
Of course, tomato pruning isn't a required chore, no matter which type of tomato you're growing. If you're not concerned about growing large fruit or trying to keep the plants under control, you don't need to worry about pruning.
How to Prune Tomatoes
If you decide to prune, it's really a very simple process. Look for the tomato "suckers," which grow in the "V" space between the main stem and the branches on your tomato plant. If left unpruned, these suckers will eventually grow into full-sized branches—adding lots of foliage and, eventually, a few fruits. This will also result in a tomato plant that quickly outgrows its space in the garden.
To prune, you simply remove these suckers. Suckers under two inches long can simply be pinched off with your fingers, but with larger suckers, use a pair of clean pruners, disinfecting them as you move from plant to plant to protect against spreading diseases. Whenever possible, remove the suckers when they are small. Removing large amounts of foliage at one time can stress the plant.
Branches that are low-hanging and touching the ground should either be staked up or removed. Leaves touching the ground can be susceptible to bacteria, fungi, and viral infections that can spread through the rest of the plant.
It really is that simple. Pruning is a chore that can be done while watering or weeding and results in healthier indeterminate tomato plants and bigger fruit—with very little effort.