How To Know When It's Too Late To Prune Tomato Plants

In the seemingly peaceful gardening world, there are rumblings of dissent. Little more has gardeners ready to throw off their gloves than questions about pruning tomatoes. Okay, no one is likely to resort to a punching match about the issue, but, like other pruning-related queries, master gardeners, avid amateurs, and professionals don't have a black-and-white answer to the conundrum of when is too late in the season to prune your tomato plants. After perusing the input from experts and otherwise, the answer appears simply to be "It depends."

The factors at stake include the types of tomatoes you're growing, your climate, and, frankly, whether you want to or not. First off, determine (pun intended) whether you have determinate or indeterminate tomatoes; in general, you don't need to prune determinate tomatoes, while indeterminates benefit from strategic trimming. But we need more information to prune our determinate ones correctly. 

As you're wading through your late-summer and early-fall vegetable garden, looking for the smartest ways to maximize its limited tomato-growing time this year, take into account these things: How long do you have until your usual first frost? What are the daily high temperatures? And lastly, is time in the hammock with a good book more compelling than spending time elbow-deep in tomato vines? If temperatures haven't dropped significantly, and that last option isn't as tempting as a potential bumper crop of tomatoes, you still have some time and a few pruning options available.

By early September, some northern areas and high altitudes are within just a few weeks, maybe days, of a frosty morning. Conversely, some spots may have months more of scorching sun, and the fruit may desperately need the protection of shade. In short, up north and up high (altitude), it's too late to do any heavy pruning. Down south, where summer stretches well into October, you can have a heavier hand when with the snippers, but still exercise some restraint. In any zone, early fall gives you a chance to do a bit of plant matter removal. Dead branches and leaves are always good to get rid of, since this can improve air circulation and prevent diseases and pests.

If frost is just around the corner, light pruning to improve air flow is a smart practice. Tell your plant it can invest all its energy in ripening the fruit that's already set, by pinching away new blooms and small fruit that won't ripen in time. For those within 6 weeks of the typical first frost, topping the plant (cutting away the top of your plants) can help divert its energy toward ripening the existing fruit. This process tells the plant to stop producing new flowers and fruit and to siphon energy toward ripening fruit that's already set.

Poorly planned snipping is one of the biggest mistakes you can make when pruning tomatoes. Be sure to reserve enough leaf cover in hot regions to protect ripening tomatoes from extreme sun. Too much direct, hot sun can make fruit suffer from sun scald (pale, damaged spots). Maintaining shade on your ripening fruit can also help prevent splitting and cracking.