One of our most frequently asked questions on the farm is, "Should I prune my tomato plants?" followed closely by, "How do I prune tomatoes?" There are some basic guidelines to tomato plant pruning, but by no means should you be intimidated by it. With this fairly simple tutorial, you can be out pruning your plants for better taste and disease resistance this afternoon! If you are still unsure by the end of this tutorial, our Tomato Masters Workshop will give you a hands-on learning experience of how to properly prune your tomatoes--along with even more tomato-afficionado knowledge on how to improve their yield, taste, and vitality.
You should start by identifying and counting your main plant stems. For any tomato variety besides cherries, you should aim for 6 to 8 main stems; however, if it's late in the season and you have more stems than that firmly established, you can refrain from butchering your plants--there's always next season to aim for that 6 to 8 number we recommend. For cherry tomato plant varieties, you can have as many as 12 to 14 main stems.
The next step is learning how to identify what are commonly called "suckers." These are officially called apical meristematic plant tissue. You can begin pruning your suckers once you have 6 to 8 main stems already established (12 to 14 for cherry tomatoes). Here is a photo of a sucker, or apical meristem.
The sucker is the junction between your stem branch and a leaf - it is always above a leaf. It juts out at about a 45 degree angle in this joint. You can locate most suckers by following your leaves back to their main stem. Your suckers will turn into main stems unless they are pruned. These stems will develop their own leaves and flowers, but you want to prune them in order to give your plant more air flow in the center, which will reduce your risk for diseases and pests. Allowing more light into the center of the plant will also improve the flavor of those fruit.
Another important, but easy, method of fighting disease is to prune any leaves touching your soil. Many pests and diseases reside in the soil, and foliage in direct contact with soil is more prone to developing disease and pest issues. We've learned over the years that even minimal soil contact with your leaves can be bad news, and you're better off pruning these leaves than leaving them as pathways for diseases and pests to infiltrate your plant.
You can see in the tomato rows above, we've removed most of the leaves at the base of the plants (we do these as they grow tall, not in the beginning of the season). You can also see the straw mulch we've placed to further help with soil splash up during watering. The mulch also serves to keep the soil cool in the latter part of a hot summer, suppressing weeds and reducing irrigation frequency.
We also remove some leaves on the interior of the plant to allow more light and air flow into it. We want the tomato plant to be able to shade its fruit, otherwise a sun scald will form on it. So there is a fine line between taking off too much foliage and not enough.
If your season is short, or if you are in low light areas (such as coastal fog or shade trees), then the more leaves and suckers you should prune off.
Towards the end of your season (after September 1st in the Santa Cruz Mountains), you can start topping off your plants if they become too large. New vegetative growth at this time most likely will not bear fruit, so you're better off having your plant devote its energy to fruit production on existing flowers. For a more detailed explanation and hands-on approach to these techniques, check out our Tomato Masters Workshop at the farm.
You can find more information all about tomatoes on the World Tomato Society website.