Answer: To answer the last part of your question first, there's really no way to predict when melons will be produced and when they will mature - it all depends upon the growing conditions and varieties.
There are different ways to determine the ripeness of different varieties of watermelons. I think the best method is to look for a "mellow yellow belly" - the spot where the fruit touches the ground. It should be a buttery yellow. You can use these other signs to help you pinpoint ripeness: there's the "thump" method - if rapping on the melon produces a sharp sound, it's still hard, not ripe inside. A duller thump means it's softening, getting closer to ripe. A really dull dead sound means it's probably overripe. The other clue is the little tendril on the stem closest to the fruit. It looks like a tiny curly pig-tail. When that browns, it signals (in some varieties), true ripeness. Enjoy!
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