That sounds like over watering. Do you check the soil to make sure it needs water before you water?

Could be overwatering, not enough fertilizer as well.

Josh

I was checking at the beginning, but not so much anymore. I'll pay attention to that from now on though. Thanks!

Watermelons do best in the ground. Loam the soil up with leaf mold.

I've successfully grown sugar baby watermelons in half whisky barrels holding about 25 gallons for four years. They do need to be kept evenly moist and fertilized generously. But I let the top few inches of the mix dry out before watering. I usually give them about 5 gallons of water every two or three days when the weather warms up and they're growing rapidly. I grew mine in 5-1-1 with controlled release fertilizer added in at planting. I also fertilized with Miracle Gro 24-8-16 soluble fertilizer every two weeks. My guess is that your watermelon is getting too little water too often and not enough fertilizer. If you want to stick to organic fertilizers, I suggest you add fish emulsion for the nitrogen.