All my watermelons and cucumbers so far that have been on the ground, even with something under them, have gotten a black spot on the end of them, which then spread over the rest of them and rotting. The couple of cucumbers that have grown on the fence look great. Also, can cantaloupes be climbers?
Can Cantaloupe Be Climbers?
Certified GKH Gardening Expert
Like other fruits and vegetable plants, watermelons and cucumbers 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.
On the off chance that it could be fungal related instead, you can treat the plants with neem oil, which is both safe and effective.
As for the cantaloupe, you can also plant cantaloupes along a fence or allow the plants to climb a trellis or small stepladder. Just make sure to add something that will cradle the fruits as they grow—such as a sling made from pantyhose—or set the fruits on the steps of your ladder.