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How to Prevent Zucchini Blossom End Rot

Zucchini Blossom End Rot and how to prevent it

Zucchini typically grow like crazy no matter what and produce more than almost anyone can eat. The problem I had was blossom end rot. Over the years, I have come across two different kinds of Blossom end rot. Unfortunately, both types have similar symptoms. As soon as the zucchini started to put on, the ends would start to turn yellow, then soft, and start to rot right on the vine. Doing some research and testing my theories, I have discovered preventative methods for both types.

A calcium deficiency in the soil causes the first type. Zucchini need calcium to provide the proper cell structure for the fruit to hold its shape. This type can be identified by how the zucchini grows. First, they will start to grow as normal, but before they get to any harvestable size, the blossom starts to turn yellow, soften, and start to rot.

To remedy this, I bought a bag of calcium carbonate and scratched it into the soil’s surface, being careful not to disturb the roots too badly. I also mixed it in a bucket of water as well and used that to water the plants. I continued this regimen once a week for the rest of the growing season. As a result, I maintained a high level of calcium in the soil and started to have beautiful zucchini to harvest right up until the first hard frost.

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The second type of blossom end rot is caused when the flower is not pollinated. To determine if this type of end rot is what you are up against, all you will need to do is inspect the shape of the fruit. Typically, instead of rotting on the end and the whole thing withering, only the ends rot, and the portion next to the vine turns into a bulbous shape. Another sign is when only a few blossoms are affected. Sometimes, the older fruit will be growing just fine, or the younger fruit will be growing just fine.

The culprit here is not having a male blossom blooming at the same time. The affected blossoms may have started blooming before the male blossom was blooming or just after it had wilted away. The heavy thunder and hailstorms we have here in Colorado often tear up the male blossoms.

To identify what blossom is a male, you will want to look for one that does not have any fruit starting below it. It is often bigger than the female blossoms. To help ensure you have a male blossom blooming as often as possible to minimize this type of end rot, you can plant at least two separate zucchini plants. If you plant them at least a week apart, they will mature at a different rate, and you increase your chances of having them bloom at different times. This will help ensure you will always have a male blossom blooming for the bees to pollinate the rest.

I now practice till in some calcium carbonate into the soil, where I plan to plant the zucchini and plant at least two plants to minimize blossom end rot.

Now, what do you do with all those zucchini?


I’m the owner of Benham Design Concepts, a mixed media art studio where I design and build custom furniture and other works of art using wood, glass, stone, and various metals.
In this blog, I talk about the art I create, my journey, and the things I learn along the way.

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