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As the heat of summer ascends and some garden plants wither and fade, one of the thriving and often rambunctious plants is the tomato. Most heirloom tomatoes are indeterminate, meaning they keep growing and growing, sometimes reaching upwards of 10 feet high if trellised. Just as you would with fruit trees and bushes, these varieties of tomatoes can be pruned to yield a higher volume of better tasting fruits. Since indeterminate varieties set so much foliage, the idea behind pruning is to cut back and shape the foliage as much as is reasonably possible in order to direct the plant's energy and nutrients to its fruit.

Step 1: Understanding the plant.

The tomato plant has a main stalk, which is what you want to preserve when pruning. Between the leader stem and the branches grow suckers, shoots that can grow and form their own branches, suckers and fruit.

The main stalk is on the left, the sucker is coming out between it and the branch at a 45 degree angle.

Upclose: The sucker.

Step 2: What to take off.

Pruning starts the day you plant. In the first act of pruning, pluck off any branches that will come in contact with the ground when the plant is planted. A few weeks later, you will notice that your plants are fuller, taller and beginning to fill out with many branches and suckers. This is the most important time to prune! Begin by identifying the main stalk, then prune off the suckers. I leave the main stalk plus one sucker if the plants are big, some people might choose to prune to one stalk regardless.

A tomato plant pruned to a main stalk a few weeks ago.

The same plant, being pruned again as it grows.

Throughout the season, you will need to periodically remove suckers. This will keep your plants manageable and will encourage fruit to ripen as the season progresses to its end. In addition to suckers, prune diseased or yellow leaves. These usually appear at the bottom of the plant.

Step 3: What to leave on your plant.

Once you get used to pruning, it might be hard to stop. However, some moderation is needed to keep a good balance with your plants. In the beginning of the season, it's important to prune, but as the season progresses, heavy pruning is not as necessary, especially if you do a good job shaping and staking the plant. I never have just one main stalk by the height of the season. I usually allow a few more to grow, while pruning most suckers off. This helps prevent sun scald and enables the plants to have more fruiting stalks. This is especially important for varieties such as Brandywine or Striped German, which don't set much fruit in the first place. Remember, the plants needs foliage to survive, just not all of it.

This plant has been pruned to a branching stalk. Can you spot the unwanted sucker? It's at the top left corner.

Notes:

• This post covers indeterminate tomatoes, but there are 3 more classifications: Semi-determinate, Determinate and Dwarf. Semi-determinate tomatoes grow like indeterminate ones, and then stop. It's important to prune these varieties in the beginning of the season and then stop once the plants start setting fruit. Determinate varieties should not be pruned. Dwarf tomatoes are determinate as well, and should not be pruned either, except to remove any yellow or diseased leaves.
• At the end of the season, a few weeks before the last frost, some growers choose to "top off" their plants by lopping off the foliage above the last fruiting cluster to help the fruits ripen. I don't use this practice, but many do, especially areas with shorter growing seasons.
• When pruning off larger suckers that have turned into thick stalks, use pruning shears to keep from breaking or tearing the main stalk. Anything that is very large might actually harm the plant to remove, so consider leaving very thick stalks, and be more diligent about pruning tender suckers in the future.
• Sometimes new suckers grow from the base of the plant later in the season, even after the base has previously been pruned. Be on the look out for these unruly suckers and prune them off when you spot them.
• Keep your plants healthy and only prune and and stake them when they are completely dry. Most devastating tomato diseases spread through water contact.