Plant the watermelon seeds after all danger of frost has passed. From planting to harvest, the watermelon takes between 70 to 85 days, depending on the variety. The watermelons in your garden will give you subtle signs when they are ready for harvesting. As they ripen, their color dulls and the rind hardens. Some of the signs you see in the garden won't be the same things to look for when selecting watermelon at the produce stand.
Look at the curling tendrils on the vine nearest to the melon. If they are dry yet the leaves and vine look hearty and alive, is an indication the watermelon is ripe.
Lift the watermelon gently and press your fingernail on the rind area that rests on the ground. The rind that lies on the ground will be tough and resist your nail's imprint if the melon is ripe.
Turn the melon over, if you are at the produce stand and not in the garden. Look for the area where the melon rested on the ground, while still in the garden. If ripe, this area will be yellowish or cream in color. A green or white ground spot indicates that the watermelon is not ripe.
Thump the watermelon rind with your finger. If ripe or over ripe, the melon gives a dull thud, while an unripe watermelon produces a hallow or ringing sound.
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