Watermelons not growing well.
This is my second year growing watermelons. This year I dug my holes 3 feet deep and added composted manure into the soil. I planted them 3 plants per hill over black landscape fabric. The seeds I bought from Lowes. Crimson Sweet and Carolina Cross. I have over a dozen melons growing now and all of them growing distorted and wont grow larger than 7 or 8 pounds. I have fertilized them 3 or 4 times so far and water them twice a week but they wont grow any larger. What am I doing wrong? I have a couple ideas, such as my source of seeds, maybe my soil needs sand and one plant per hill. Next year I am going to try getting my seeds from Willhite.
Thanks in advance