Blossom end rot is common disorder that can affect zucchini and other members of the squash family. This disorder is caused by a calcium deficiency in the developing fruit, which can result in the appearance of a dry, sunken, and darkened patch at the blossom end of the zucchini.
The calcium deficiency can occur due to a number of factors, including inconsistent watering, extreme temperatures, or imbalanced soil nutrients. When the plant experiences stress from one or more of these factors, it may be unable to take up enough calcium from the soil to meet the demands of the developing fruit. As a result, the cells in the fruit become damaged, and the affected area can become susceptible to secondary infections by fungi or bacteria.
To prevent blossom end rot in zucchini, it is important to maintain consistent watering and to avoid allowing the soil to become too dry or too wet. I don’t think either of those is the issue because I keep close tabs on how much water these are getting. I water these by hand and they drain very well.
Experts recommend adding calcium to the soil or using a calcium-rich fertilizer to help prevent or mitigate the symptoms of blossom end rot. I found a water-soluble calcium nitrate solution and I used it to treat my zucchini. It’s as simple as adding 1 teaspoon per gallon of water, then watering your plants as you usually would. I hope this helps you in the garden!