Deciding when a melon is ripe can be one of the trickiest parts of having grown them. A cantaloupe is ripe when it has a noticeable fragrance and the fruit comes off the stem with just a light tug.
To harvest, lift the cantaloupe until it separates easily from the vine. To make cantaloupes even sweeter, hold off watering a week or so before harvesting, but then resume watering if you have more fruit, and don't let the vines wilt.
Honeydews are ripe when the place where they rest on the ground has turned white. Other late melons are ready when they have a strong, sweet smell and the blossom end is slightly soft. Their rinds should also have turned dull. Late melons should be cut from the vine with a knife or 
shears.
A watermelon is ripe when it makes a dull "thunk" when you rap on it.
The skin on the underside should have turned pale yellow, and the tendrils at the stem should be dark and withered. It, too, should be cut and not pulled from the vine.
More about gardening with melons:
