Charleston gray watermelon has developed black rot

Question

At the end of my Charleston gray watermelon has developed black rot. What is the cause of this? The watermelon was growing well up until this week, then I saw black rot on the end.

Answer 1

Watermelon can suffer from Blossom End Rot.
This is a lack of Calcium.
Here is a link that explains the issue.
https://www.gardeningknowhow.com/edible/fruits/watermelon/blossom-rot-in-watermelons.htm