Why don't my watermelons ever put out melons?

Why doesnt my watermelons ever put out melons? The plant look good it puts out lots of flowers but no melons.

They need tons of fertilizer. They;re very heavy feeders. I would try Miracle-Gro Water Soluble All Purpose throughout the whole growing season, and they need good fertile soil. You mught want to do a soil test and add potassium or phosphate if the soil is lacking.