Examine the rinds and wait for their shine to become dull. Seedless watermelons should also feel rough, not smooth as they do when they are not ready for picking.
Lift up the seedless watermelons and look at the area where they lay on the ground. This area must be yellow in color, not green or white.
Examine the curly tendrils near where the stems meet the seedless watermelons. When the melons are ripe for picking, these tendrils are dry, brown and look dead.
Knock on the seedless watermelons and listen for thumping or hollow sound. This method is not fool-proof, but is sometimes another indicator that the melons are ripe.
Slice into one of the seedless watermelons that you think is ripe and remove a wedge. The flesh should be red and it should taste sweet. If it is, the melon and others like it are ready for harvesting.
Cut the vines to harvest the watermelons. Leave about 1 to 2 inches of the stem on the watermelons. Keep the melons at room temperature, then chill them in the refrigerator about three or four hours before serving. In general, watermelons stay ripe at room temperature for about two weeks.