I am located in Central Florida and have been trying to grow watermelon in my 8ft x 4ft 10 in raised garden bed filled with organic soil and miracle grow garden soil. I have had this same problem now 4-5 times with the fruit as it begins to grow. On the top side of the fruit, farthest from the connection to the main plant, a dark black spot begins to form and in a matter of days it begins to grow larger and larger until engulfing the entire watermelon. I can send a picture if you can give me an email address. It is almost as if it begins to rot, but the watermelon is not to full size yet. Sometimes it happens on the small melons that have just begun to grow. Other times, it happens when they are half way through growing or larger. Any help would be great!!
Watermelon Fruit Problems
Certified GKH Gardening Expert
Like tomatoes, peppers, and squash, watermelons can also be affected by blossom end rot. This condition happens due to a calcium deficiency. Calcium helps a plant create a stable structure. If a plant gets too little calcium while the fruit is developing, the end result is what you're experiencing. There are a few things you can try for blossom end rot treatment.
Water evenly, not too much or too little. Add a low nitrogen fertilizer to the soil, for optimal calcium uptake. Add lime to balance the soil’s pH if it is too low, (should be between 6.0 and 6.5). Add some gypsum to the soil for additional calcium. In addition, remove affected fruit and use a calcium rich foliar spray on the plant.