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Your squash and zucchini are rotting on the vine because of a fungal issue called blossom end rot, poor pollination, or inconsistent watering.
If you’ve been asking why your squash and zucchini are rotting on the vine before you even get a chance to harvest them, you’re not alone.
This is one of the most common frustrations for home gardeners growing summer squash.
The good news is that in most cases, this rotting on the vine issue is fixable once you understand what’s causing it.
In this post, we’ll cover the main reasons why squash and zucchini rot on the vine, how to stop squash and zucchini from rotting on the vine, and what you can do to keep your plants healthy.
Let’s dig in.
Why Your Squash and Zucchini Are Rotting on the Vine
Squash and zucchini are rotting on the vine for a few key reasons, and identifying the culprit is the first step to fixing the problem.
1. Blossom End Rot
Blossom end rot is the number one reason squash and zucchini rot on the vine.
It shows up as a dark, sunken, leathery spot on the blossom end of the fruit — the end where the flower used to be.
Blossom end rot isn’t a disease; it’s a calcium deficiency caused by inconsistent watering.
When your squash or zucchini plant can’t take up calcium properly, the fruit starts rotting on the vine before it matures.
This happens most often when the soil dries out between waterings or when there’s too much nitrogen in the soil.
2. Poor Pollination
Poor pollination is another big reason squash and zucchini rot on the vine.
If female flowers don’t get enough pollen from male flowers, the fruit starts to grow but then shrivels and rots because the seeds inside never develop properly.
This is especially common early in the season when bee activity is low or during rainy stretches that keep pollinators away.
You’ll notice the fruit turning yellow and rotting from the blossom end just days after the flower drops.
3. Overwatering and Poor Drainage
Squash and zucchini rotting on the vine can also be caused by too much water.
Waterlogged soil leads to root rot, which weakens the plant and makes the fruit more likely to rot on the vine.
If your soil doesn’t drain well, or if you’ve had heavy rain, your squash and zucchini can develop fungal problems that cause rotting on the vine.
4. Fungal Diseases
Several fungal diseases cause squash and zucchini to rot on the vine, including choanephora rot and phytophthora rot.
These fungi thrive in warm, humid conditions and can spread quickly through your garden.
Fruit affected by fungal rot often develops a fuzzy mold or soft, mushy spots that spread fast.
How to Stop Squash and Zucchini From Rotting on the Vine
If your squash and zucchini are rotting on the vine, here’s how to stop it.
1. Water Consistently
Water deeply once or twice a week rather than shallow daily watering.
Consistent moisture helps your squash and zucchini take up calcium, which prevents blossom end rot and stops fruit from rotting on the vine.
2. Hand-Pollinate Your Plants
If pollinators are scarce, hand-pollinate your squash and zucchini to prevent fruit from rotting on the vine due to poor pollination.
Use a small brush or pick a male flower and transfer pollen to a female flower.
3. Remove Affected Fruit
Pick off any squash or zucchini that are already rotting on the vine.
Leaving rotting fruit on the plant attracts pests and spreads disease, making more of your squash and zucchini rot on the vine.
4. Improve Soil and Drainage
Add compost to improve soil structure and drainage, which helps prevent squash and zucchini from rotting on the vine.
Avoid over-fertilizing with nitrogen, as this makes blossom end rot worse.
So, Why Are My Squash and Zucchini Rotting on the Vine?
Squash and zucchini are rotting on the vine because of blossom end rot, poor pollination, overwatering, or fungal disease.
The fix is usually about consistent watering, better pollination, and removing affected fruit before it spreads.
Once you address these issues, your squash and zucchini will stop rotting on the vine and you’ll finally get the harvest you’ve been waiting for.