Like tomatoes, squash, eggplant etc watermelon is a fruiting vegetable. There are 4 commonly used signs that a watermelon is ripe. 1. The tendril where the stem attaches to the vine has dried up . 2, the area where the melon sits on the ground has changed color(easy with dark colored melons, more difficult with white melons) 3.The filmy glaze has faded. 4. Thumping (takes a good ear and experience but quite effective when perfected).

Ripe means a watermelon has completed its reproductive cycle. Sweetness is a characteristic of the variety and its growing conditions. There is wide variance among varieties for sweetness. Growing conditions including shade, stress, incomplete pollination etc can severly affect sweetness.