Why Your Winter Squash is Rotting From the Bottom in October – and How to Save the Rest of Your Harvest

Winter squash is so easy to grow but dark or soft patches around the fruit’s base is a common challenge in October, indicating end rot. Rotting bases are such a disappointment in fall, just as you’re looking forward to a harvest of butternut, acorn, honeynut and other winter squashes like spaghetti and delicata squash.

Don’t fear the worst, though. End rot on winter squash in October is easily fixed, so great work getting here to Garden ER where you'll find straightforward solutions to treat this season’s biggest planty problems. Act fast and you don’t have to lose your entire harvest. Identify and fix the issue, sand you'll save the rest of your homegrown gourds from a similar fate.

If you’re growing winter squash this season, it’s useful to know the signs to look out for, and what they indicate, even if you haven't noticed any dark patches on fruit bases, so you can take swift action at the very first whisper of a rotting bottom. Come on in to Garden ER and let’s diagnose and treat those ugly patches on the bases of your winter squash.

Triage: Take a Closer Look at That Base Patch

A winter squash rotting from the base up is easily spotted. A discolored patch on the bottom of the gourd appears: it may look darker, bruised or as if it’s been soaked in water. The spot will gradually grow larger and turn black or brown, and often becomes flat or slightly sunken. Press it and it’ll feel a little softer or spongier than the rest of the squash’s firm skin.

If the rotting base has been developing for a while, the patch may have collapsed into a hole, become moldy or emit a foul smell.

A healthy squash will have a base that's firm, with the spot where the blossom once grew having developed into a dry, pale, roughly circular patch.

Diagnosis: What’s Causing the Rot?

While you can’t help the affected squash’s rotting bottom, it’s vital to diagnose what caused it so you can save the rest of your harvest. While plants grown at ground level are vulnerable, end rot is also a common issue when growing winter squash vertically up a trellis.

Blossom End Rot

Blossom end rot is the most common reason, caused by a lack of calcium in the fruit which leads to weak cell walls. The problem isn’t typically a lack of calcium in the soil, but the plant's ability to take up and use the calcium. And the underlying cause of this is typically acidic soil, drought or inconsistent watering.

If blossom end rot is the problem, the rotting patch at the base of the fruit will look even and will have a brown, leathery, sunken appearance. Because calcium is used to build cell walls as the gourd grows from its base, deformed fruit formation is another clue that you’re dealing with blossom end rot.

Wet Ground

Contact with wet ground is the next most likely cause of end rot on your squashes. With more rain and cooler temperatures, it’s common at this time of year for the soil to remain moist. Contact softens the rinds where fruits are resting on permanently damp ground, giving pathogens like soil-borne fungi and bacteria a chance to start rotting the fruit.

Distinguishing between wet ground and blossom end rot being the cause is simple. Look at where the rot occurs: if wet ground is the cause, the fruit will likely look healthy except for the portion in contact with the soil; blossom end rot causes more even rotting, though it’s likely to be worse at the base.

Pest Damage

Pests are the least likely source of rot in squash ends in October, but it's a possibility. If pests start gnawing on the end of a fruit, the open wound can quickly become infected and start to rot. Signs of pest damage such as bites and holes will be clear, and these wounds are very likely to start rotting if they’re in contact with wet ground.

Treatment: Protect Your Current and Future Winter Squash Harvests

1. Remove Rotting Winter Squash

Squash already affected with rotting bases cannot be saved, and rot can spread and contribute to worsening conditions for the rest of the plant. Cut fruit from the plant with a sharp pair of hand pruners, as soon as you spot the first signs of a rotting bottom.

If you’ve caught the problem early and the problem is wet ground or pest damage, the squash is still safe to eat – just cut away the affected part with a safety margin of a good inch of healthy flesh. Inspect the flesh and if it’s firm, hard, smells sweet and has its usual color, it’s safe to cook.

If blossom end rot is the cause, dispose of the squash even if the patch is still tiny. Because the calcium deficiency affects the fruit’s growth, the flesh is likely to be less sweet.

Regardless of cause, throw out any fruit that has a lot of rot, is very soft or leaking, or has a bad smell.

2. Check Soil pH

As acidic soil is a common cause of blossom end rot, check pH levels. A comprehensive soil meter such as this from Amazon tests pH along with moisture levels, temperature, sunlight intensity and soil fertility so is a really handy helper when you’re growing vegetables. If you simply want a fast answer to whether your soil is acidic or not, test strips such as Rapitest Soil Test Kit, also from Amazon, is a quick and cheap method. Testing your soil is a smart move, however you choose to do it, as it'll alert you to any deficiencies that may be affecting others crops too.

Your local extension office can provide guidance on how to lower the acidity of your soil if results reveal a low pH level.

3. Water Consistently

Good watering practices lowers the risk that remaining fruit will develop blossom end rot. Aim to keep soil consistently moist rather than letting it dry out completely and then soaking it. Water at the soil line low to the ground near the stem, keeping leaves and fruits dry as excess moisture on squashes can contribute to rot, especially in cooler fall temperatures.

A soaker hose such as this Kink-Free Flat Soaker Hose from Walmart is a simple solution, or you’ll find some great deals on drip irrigation starter kits now summer’s over, like this Garden Irrigation System, also from Walmart.

4. Lift Squashes Off the Ground

Elevating developing fruits off the ground is a great way to prevent rot, keeping them off damp soil. It can be as simple as placing individual fruits on top of rocks or wood planks, or lay straw under the lot. A wheat cover straw such as CleanStraw mulch, available from Walmart, is ideal. Don’t worry about a few seeds being left among the threshed straw – wheat seedlings are shallow-rooted and very easy to pull up.

Move young fruits carefully so you don’t damage the stems.

5. Improve Airflow

Good airflow around plants will also reduce localized moisture and the risk of rotting. Adding a layer of straw over the soil will do the job of improving airflow as well as lifting fruit off the soil, but general care will help, too. Squash plants tend to get very dense with vegetation as they grow so regularly remove any yellow, damaged or mildewed leaves, being careful not to prune healthy leaves too aggressively as plants need these to make energy.

You can also boost airflow by removing debris under and around the plants, especially around the fruits. A small hand rake like Fiskars Xact Hand Rake, available from Lowe's, makes the job easier.

6. Harvest Sooner

Keep a closer eye on your squashes once October arrives, and harvest them as soon as they’re ready. The longer they sit outside, the more likely they are to rot. Signs they’re ripe and ready include a full, mature color, a hard rind that resists your fingernail, and a dried or hardened stem.

The hard rind of winter squashes mean they store well, so even if you have a glut, harvest what you can, as soon as you can.

Patient Notes: How Zone Affects End Rot

If You Garden in a Cold Zone

In colder growing zones, early cold snaps, shorter daylight hours, and damp fall weather in October can slow down root activity, making it harder for plants to transport calcium efficiently to developing fruit, making this a likely cause behind blossom end rot.

If You Garden in a Warmer Zone

In warmer zones, late-season heat and drier soil accelerates plant growth and transpiration, which can cause severe moisture fluctuations, making inconsistent watering a likely trigger for blossom end rot.

More Garden ER Help

Every week, the Garden ER series brings you simple solutions to this season's most pressing problems, for happy and healthy plants without any hassle.