How to prune tomatoes
When deciding whether or not to prune your tomatoes, or how to prune them, it is necessary to determine the type of tomato you are growing. Are you growing a determinate, or an indeterminate type of tomato? Your seed packet should tell you which of these types you are dealing with.
These tomatoes are also sometimes referred to as bush tomatoes. They will grow to a predetermined height, usually around three feet tall. Pruning determinate tomatoes does not affect the plant vigor or fruit size therefore it is not necessary to prune these. I do prune out any suckers that are growing beneath the first flower cluster, and I prune out leaves that are touching the ground. If you have branches or leaves that are on the ground, your tomato plant is much more susceptible to insects and disease.
Indeterminate tomatoes are just that, their growing height and fruit size is not determined, so pruning can have a positive effect. Like the determinate tomatoes, it is a good idea to keep the suckers pruned beneath the first set of flowers. Also, make sure to keep branches and leaves off the ground. These tomatoes can have one to many stems. You should however keep the stem count within four. The fewer the stems you have, the larger the fruits, but conversely if you want lots of smaller fruits, you can allow up to four stems to form. If you want a multiple stemmed plant, let a second stem grow from the first connecting point above the first fruit. If you want another stem on this plant, let a third stem grow from the second connecting point above the first set fruit.
I personally like smaller but more fruit, so I just keep up with the suckers, and I will prune out branches as needed. Also, if my tomato plants are smaller than I would like when they start to flower, I will pinch out the flowers. This sends more energy to stem and leaf growth, as opposed to flower and fruit growth. This will result in more tomatoes later, because large tomato plants will ultimately produce more fruit. I will however let some of my tomatoes flower early, so I can start harvesting sooner. I usually let my container grown tomatoes flower early, because I don’t want these to grow too big, as their root system only has so much pot space.