It's not easy to tell a ripe watermelon, in part because even a ripe uncut watermelon puts out no telltale odor.

Tap the melon. If the it sounds hollow - if you hear a dull thump -  the melon is usually ripe. An unripe melon

gives a tight, slightly metallic sound. When I grew watermelons, this method worked for me. When I bought watermelons frequently, it still worked. This technique has its limitations, however. An overripe melon will make the same sound as a ripe one.

Look for the spot where the melon rested on the ground. It it's white, the melon is unripe. If it has turned buttery yellow, the melon is ripe.

Melons with seeds tend to have better sweetness and flavor than seedless ones.

While whole watermelons are the best value, small families and those with limited refrigerator space will prefer a cut section. Choose a piece that has a dark reddish-pink color and has a split in it. Do not buy a piece that has begun to look mushy or mealy. It is overripe and the pleasure of biting into that slightly crisp flesh will be missing. 

Do not wrap any cut melon - watermelons or otherwise - with plastic unless you can finish the piece in three or perhaps four days. Wrapped melon will ferment or mold. Unwrapped melons will slowly lose water - making them sweeter - but keep up to 10 days with fine eating quality.

Tap the melon. If the it sounds hollow - if you hear a dull thump -  the melon is usually ripe. An unripe melon

gives a tight, slightly metallic sound. When I grew watermelons, this method worked for me. When I bought watermelons frequently, it still worked. This technique has its limitations, however. An overripe melon will make the same sound as a ripe one.

Look for the spot where the melon rested on the ground. It it's white, the melon is unripe. If it has turned buttery yellow, the melon is ripe.

Melons with seeds tend to have better sweetness and flavor than seedless ones.

While whole watermelons are the best value, small families and those with limited refrigerator space will prefer a cut section. Choose a piece that has a dark reddish-pink color and has a split in it. Do not buy a piece that has begun to look mushy or mealy. It is overripe and the pleasure of biting into that slightly crisp flesh will be missing. 

Do not wrap any cut melon - watermelons or otherwise - with plastic unless you can finish the piece in three or perhaps four days. Wrapped melon will ferment or mold. Unwrapped melons will slowly lose water - making them sweeter - but keep up to 10 days with fine eating quality.