– Watermelon Vines. A key indicator of a watermelon’s maturity is the tendrils or pigtails on vines change from green to brown. … – Watermelon Color. Another indicator to take note of is the color of the spot on the watermelon. … – The Sound of a Ripe Watermelon. Give the watermelon a thump. Read … Continue reading How do you tell if a watermelon is done growing?