How to Prune Indeterminate Tomato Vines

Finally, it’s summer. The season of barbecues, fireworks, and garden fresh tomatoes right off the vine.  And by the end of summer, those tomato vines have usually become sprawling monsters that hog the entire garden. But the flavor of those home-grown tomatoes is well worth it, right? Of course it is, but if you’re growing indeterminate tomato varieties - that is, types that continue producing new leaves and flowers throughout the entire growing season, unlike determinate or bush varieties that reach a finite mature size, and yield one harvest - then you could actually increase that fresh tomato euphoria by pruning the vines.  Plus you’ll have a neater looking garden with more sunlight and space for your other garden plants to hit their stride, too.

Improved Air Circulation

Removing unneeded foliage from tomato plants  - especially the 18” or so of space right above the soil surface - increases air flow around the plants, and encourages vigorous growth. Pruning leaves and branches from the bottom third of the plant also helps prevent mildew and moisture related diseases which thrive in the wet environment that a dense tangle of lower branches creates just above the soil surface. Diseases like septoria and early blight often live in garden soil, and removing the lower branches helps reduce the chance of these soil-borne diseases from  splashing up onto the foliage. Plus, your garden is instantly more inviting, and with all those unruly branches out of the way, it’s much easier to spot weeds and insect pests while there’s still time to take action.

Larger Fruit

Timely pruning diverts a tomato plant’s energy toward growing and ripening fruit instead of simply producing new stems and leaves. Pruning may reduce the total number of tomatoes you’ll yield in a season, but the average size of each tomato will be larger. Just be sure to save the leaves right around a cluster of tomato fruits - these leaves send sugar to the developing tomatoes and also help shade and protect them from sun scald. 

Earlier Ripening

When a plant has fewer fruit, the remaining fruits ripen faster, which saves time. This can be a game-changer for feet-dragging gardeners who finally get around to planting their tomatoes when the ice cream man starts making his rounds, and the neighborhood pool opens for the summer.

At Planting Time

Pruning works best on strong, healthy plants, so when planting a new tomato seedling - especially a tall one that may have already been growing for a while - remove the lower leaves from the stem and bury the plant deeply. Tomato plants have the unique ability to turn an above ground stem into a below ground root. So, what was a spindly above ground stem, will soon become a hungry, below ground root. Goodbye gangly tomato seedling, hello stocky, sturdy tomato plant. You’ll also want to remove any flowers that are on a tomato seedling when you plant it. This ensures that energy is channeled into new vegetative growth instead of towards fruiting, which should happen much later in the plant’s life cycle.

Early to Mid-Season

As your indeterminate tomato plants begin to grow, remove any flowers until plants are at least 18” tall. This lets plants focus that energy developing a strong root system that will help the plant thrive through the heat of summer. Prune off all of the leafy lower branches - often called ‘suckers’ - below the first group of tomato fruit. Suckers form in the axil, or the part of the tomato plant where a leaf stem attaches to a main growing stem. It’s best to remove suckers while they’re small enough to simply pinch off with your fingers, which helps prevent damage to the main stem. Larger suckers should be pruned away with a clean cut at the main stem. Many tomato growers in southern areas of the US use the Missouri pruning technique, where only the small leaflets at the end of each sucker are removed, leaving two base leaflets on the plant. These will eventually grow large enough to shade ripening tomatoes, protecting them from sun scald. And to reduce the chance of spreading disease, it’s best to prune when your tomato plants when they’re dry.

Late Season

By late summer,  every tomato grower will confront the same yearly dilemma ; how much longer to wait on those sprawling tomato vines loaded down with bushels of nearly rip, full-sized, but still very green tomatoes. The smallish window to establish a fall garden closes a little bit each day that the tomato plants stay in the ground. But here comes pruning to the rescue, again. Simply ‘top’ those stragglers about a month before your area’s average first frost date, and the green tomatoes that are still on the vine will ripen faster.  ‘Topping’ simply means cutting a main growing stem above the highest cluster of fruit, which triggers the plant to cease flowering and new fruit setting, and diverts all of its sugars to ripening the remaining tomatoes. Topping helps ripen those tantalizingly large clusters of tomatoes sooner, plus any green ones still left on the vine that are plucked before the first frost are more likely to ripen indoors.