Why is my watermelons rotting before they are done growing?

Question:they split open & rot on vine

Answers:
Keep them off the ground. The dirt actually holds moisture against the melon (or any large fruit, like pumpkins...) and causes it to rot and/or mildew on the side in the dirt. Put boards, or sturdy plastic under them so water will not pool under your melon.

Also... fruits/vegetables keep growing on the vine even past the "ripe" point. Check them often once the color is right and pick them before they get past the ripe stage.