25+ Black Diamond Watermelon Seeds. You can't beat the flavor and sweetness of a home grown, vine-ripened watermelon and Black Diamond is one of the favorites of home gardeners everywhere! A round, medium sized melon with red fruit. A old Florida farmers favorite - but you won't find them in your grocery store - they don't ship as well as the new hybrids, but they TASTE SO MUCH BETTER! 90-100 day maturity, needs plenty of space, warm weather and plenty of water.