If you are growing tomatoes, it's important to know what kind of plants you have. This information will determine whether you need to prune them. If you're growing indeterminate varieties, you will need to know how to prune tomato plants in order to keep them healthy and maximize their fruit yield. Regardless of what type of tomato plants you are growing, knowing how to trim tomato plants is essential for plant health.
Which Tomato Plants Need to Be Pruned?
There are thousands and thousands of tomato varieties, most of which can be classified as determinate or indeterminate. Determinate tomato plants do not need to be pruned, but indeterminate ones benefit from pruning.
- Determinate tomatoes are small bushy plants that fruit over a single period of just a few weeks during a growing season. They generally stay under five feet tall.
- Indeterminate plants grow very tall and produce fruit continuously from the time they begin in the summer through the entire growing season until there is a killing frost.
How to Prune Indeterminate Tomato Plants
If you are growing indeterminate tomato plants, it is considered a best practice to prune them. Assuming they are properly planted and cared for, they will grow and produce fruit even if they aren't pruned. However, pruning helps keep their energy focused on producing fruit rather than foliage, leading to higher yields. It also helps the plant get the airflow it needs. This reduces its chances of becoming diseased. The main goal of pruning is to remove suckers from your plants.
1. Find the Suckers on Your Plant
Suckers are small shoots that develop on a tomato plant between the stem of the plant and its leaves. In the picture below, you can see someone's hand holding a sucker. This is the part of a tomato plant that is removed when the plant is pruned. The spot in which suckers grow is often referred to as the armpit of the plant.
2. Consider the Impact of Suckers
If left in place, these suckers will keep growing and become additional stems that will produce fruit. In theory, you would think that leaving them in place would lead to more fruit, but that is not the case. When a plant has a lot of growing suckers, it has to use a lot of its energy to grow foliage. That means you'll end up with large, often unwieldy plants with a lot of branches. They do flower and produce fruit, but the overall fruit production will be lower than if the plant had fewer stems.
3. Decide How You Are Going to Prune Your Plant
You don't necessarily have to remove all of the suckers, but you'll get more fruit if you remove at least some. Some people remove all suckers, which results in pruning the plant to a single stem. Others focus only on removing the suckers below the first set of fruit that forms. Some gardeners remove all of the bottom suckers, as well as some (but not all) of the ones that form above the first set of fruit. There isn't a right or wrong way to do it; pruning is a matter of personal preference.
- If you prune to a single stem, you'll need to trellis the plant up a string or a trellis. This can be very productive, but you'll need to check your plant for new suckers daily in order to keep up with pruning.
- If you prune only the first few suckers, your plant will still have a lot of branches. You'll probably want to grow it so that it climbs some type of trellis if you go this route, or possibly inside a tomato cage.
- If you plan to use a stick to stake your tomato plants, you'll probably want to keep an eye on the plant and prune out suckers as it grows so that you don't have to keep adding stakes to the same plant to hold it up.
4. Remove the Suckers
Once you have decided which approach you are going to take to prune your indeterminate tomatoes, the next step will be to actually remove the suckers. Start by visually inspecting each plant to find suckers that need to come off. If they are small, you can snap them off with your thumb and index finger. If they are larger, or if you'd prefer not to use your hands, use a pair of small garden shears to snip away the suckers. You can let them fall to the ground or collect them to add to your compost bin.
Topping Indeterminate Tomato Plants
Topping tomato plants isn't a part of ordinary pruning, but it is something that gardeners often do with indeterminate tomatoes toward the end of the growing season. Without being topped, indeterminate tomato varieties will keep growing taller, extending past your ability to trellis them or to reach the top to pick the fruit. By topping a tomato plant, which is simply cutting off the top of the growing stems (the main stem and any suckers you left on the plant), you can keep it from getting taller. Instead, the plant will stay at the same height and redirect its energy into fruit production.
How to Trim Tomato Plants (Determinate and Indeterminate)
All kinds of tomato plants can benefit from being trimmed periodically. This simply involves visually inspecting plants for leaves that are diseased or have sun damage and snipping them away. Examples of what you may want to trim away from your plant include:
- Leaves that cross over in a crowded in a way that would keep the plant's main stem and branches from getting good airflow
- Spent trusses from which tomatoes have already been picked and yellow or brown leaves below current fruit production (Tomatoes start ripening at the bottom of a plant and move up.)
- Leaves that show sights of being affected by garden blight, such as brown spots or browning edges on leaves
- Leaves that appear to have been affected by tomato wilt or other kinds of tomato plant diseases
- Leaves that have insect or pest damage, such as the leafminer damage shown in the photo below
Grow a Bounty of Tasty Tomatoes
Now that you know how to tell if your tomato plants can benefit from pruning and you understand how it works, you're prepared to start growing your own tasty tomatoes. If you're not sure which approach you want to take, consider doing your own experiment. Instead of pruning all your indeterminate tomatoes the same way, prune a few to a single stem, cut off only the bottom suckers on a few, and do additional pruning on some others. That way, you'll be able to discover what works best for you in your garden. After all, there is more than one right way to grow tomatoes (and prune them).