Winter squash are long-season vegetables. They can take three months or more to fully ripen, and you need to let them reach that stage if you want to store them throughout the winter. Most varieties tend to grow long, lush vines before they begin to set flower buds, which become the squash fruits. And whether you're growing them on a trellis or on the ground, the vines can often grow longer than you expected. This can mean over-crowded and heavily weighted trellises or a vegetable garden that is overrun by squash plants. However, a little judicious pruning at the right times can tame the vines without compromising the fruit.
When to Prune Squash Vines
Winter squash need a certain amount of vine to support and feed the developing fruits, but you don't have to let the vines grow forever. Most varieties will not set more than four or five fruits per plant. Once your vines have set that amount, you can begin to prune them back and keep them in check. While you are waiting for the fruits to set, it's OK to gently move the vines out of the way to make room for yourself or other plants.
How to Prune Squash Vines
If you start pruning as soon as the four to five fruits are set, the vines should be tender enough to pinch off with your fingers. Simply look for the squash that is farthest out on the vine and pinch off the tip of the vine, leaving just a couple of leaf nodes past the outermost squash.
If you've let the vines get unwieldy, you may need to cut more of the vine, to get it back to one or two leaf nodes beyond the outermost fruit. Don't worry; it won't hurt the plant. As long as the main roots of the vine are not disturbed, the plant will continue growing.
Potential Pruning Problems
One potential problem you may encounter is vines that have rooted. When squash vines touch the soil, they can send out new roots. If the part of the vine you want to remove is near a newly rooted section, you can still lift and remove that section, roots and all. It may cause the vine near the rooted section to wilt for a day or two, but it should recover quickly.
Another thing to keep in mind is that the vines may grow back. As with many plants, pruning back your squash vines once doesn't mean they won't try to grow new stems and leaves. You may have to do more pruning to keep them confined to a limited space.
Mulching With Vines
Some gardeners like to use their squash vines as a living mulch. Vines can do a good job of smothering weeds, but they also smother any plant they grow over, including other vegetables, so use them as mulch with caution. The vines are also scratchy and prickly, which makes them unpleasant to walk on and harvest through. This can work in your favor, deterring pests like squirrels, who don't like to walk on squash plants, but it can also be disagreeable for you.
A Pruning Bonus
Don't feel bad about pruning back your squash vines. It won't hurt the plant or fruits, and it won't diminish their flavor. Pruning also signals to the plant that time is almost up for the season and it needs to get a move on toward ripening. Since the plant won't be able to set any more fruits—and, by pruning, you aren't letting it grow any more foliage—it can put all its energy and resources into plumping up and ripening the existing fruits.
So even if you aren't short on space, if you are inching toward the end of your growing season, you can speed things up by pruning the vines. It's the same thing we do when we prune the excess vine or pinch off late-season buds from tomato plants, to get the existing green tomatoes to ripen. Prune away.
Alternatives to Pruning
If you don't have the space for the long, rambling winter squash vines, consider planting a bush variety instead. You'll have fewer options, but there are many good bush varieties being offered as space-saving plants. Bush varieties also yield about four to five fruits per plant, but they need only about 4 square feet of total space. You can even grow them in containers.
Pruning Summer Squash
Pruning is also acceptable and potentially beneficial for summer squash plants. Summer squash vines respond to pruning the same way as winter squash. But since we harvest summer squash while it is still in its tender, immature stage, summer squash vines will continue setting more flowers and fruits as long as they are harvested before they have a chance to mature. However, pruning summer squash results in a smaller harvest, unlike with the winter squash plants that wouldn't set any more fruits anyway.
Eventually, summer squash vines will become exhausted and begin to decline. When this happens, you can pull out the whole vine (and hopefully you will have already succession seeded a replacement plant during mid-season).