Pruning your Tomato plants is important to their overall health and to maximize your harvest. There are two types of Tomatoes, determinate and indeterminate. Only the indeterminate varieties should be pruned. Determinate plants are smaller dwarf or bush plants which only produce one large crop. If you prune these plants it will decrease your yield. Indeterminate Tomato plants keep growing and producing as long as the plant is healthy.

There are three reasons to prune your indeterminate Tomato plants:

1. Pruning keeps the plant size in check. This is especially important if you are growing your Tomatoes with other plants in raised beds or in an urban setting (urban grow kit link?) where space is at a premium. Having overgrown plants can decrease their productivity.
2. Regardless of the variety, indeterminate Tomato plants require a lot of support. Allowing the plant to lie on the ground decreases the amount of sunlight the plant may get and the number of Tomatoes the plant will produce as well as potentially the size of the individual fruit. It also leaves the Tomatoes vulnerable to slugs and other pests.
3. Pruning increases air circulation around the plant which prevents disease and helps combat insects.

When you prune you are going to remove leaves, also known as suckers, which will prevent the growth of an additional branch. A tomato sucker is a small shoot that grows out of the joint where a branch on a tomato plant meets a stem. Removing suckers does reduce the number of Tomatoes the plant will produce, but it will increase their size.  

It is best to prune in the morning on a day when no rain is expected. Pruning allows the plant to be exposed to infections, so you don’t want these wounds to get moist. First, cut the branches from the bottom of the plant by following them to the main stem and cutting there. If your plant is really bushy, you might actually find Tomatoes hidden under the foliage which have not been getting enough light to ripen. Harvesting becomes much easier once the plant is pruned. Once the plant has reached the top of its support mechanism you can consider removing the top of the plant which is known as topping a Tomato. Performing this task focuses the energy of the plant on the fruit at the bottom of the plant instead of new growth on the top. After topping the plant it can be susceptible to leaf and fruit scorch.  You may want to protect it from the afternoon sun for a few days by using an umbrella or shade cloth around the plant.