Answer: You are in for quite an adventure! Melons can cross pollinate when several varieties are growing in proximity to one another. The seeds for your volunteers are likely a mixture of two or more different watermelon types so you'll be harvesting a new variety. It will have characteristics of both parents and while I'm sure it will be tasty, it won't be the exact same watermelon as you grew last year. Watermelon ripeness is very hard to judge! Some gardeners go by the sound; when thumped a ripe melon sounds a dull thud and an unripe melon rings. Other gardeners go by the color of the spot on the bottom where the melon touches the ground -- this is more reliable in my experience. When that spot turns from white to a pale buttery yellow, it should be ready. You may also see brown tendrils near the fruit and finally, the skin may begin to feel slightly ridged. As a rule of thumb, the smaller melons tend to ripen in less than 80 days, compared to say 100 for some of the larger varieties.
Good luck with your melons!
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