How to know if a watermelon is ripe?

There are three reliable signs. First, look for the "field spot." This is the creamy yellow patch where it rested on the ground. If that spot is white or greenish, the melon isn't ripe. Second, it should feel heavy for its size. This means it’s full of water and will be juicy. Finally, give it a good thump with your knuckles. A ripe watermelon has a deep, hollow sound. A dull thud usually means it’s underripe or mealy. Also, a dull-looking rind is better than a shiny one; a shiny melon is likely not ready yet.