Type
large heirloom
Watermelon variety
Black Diamond Watermelon
A large watermelon with dark green rind and bright red flesh. It performs best in hot summer conditions and with plenty of room.
Days to maturity
85 to 90
Best for
southern gardens, big fruit
About Black Diamond
Black Diamond is an open-pollinated heirloom famous for its very large, round fruit with a dark green, almost black rind. The flesh is bright red, sweet, and firm, and individual melons commonly reach 30 to 50 pounds. Its thick, tough rind holds up well to handling, which historically made it a popular market and shipping melon.
Growing Black Diamond Watermelon
Because the melons are so heavy, give plants ample space of 5 to 6 feet and rich, well-drained soil, and keep the oversized fruit on the ground rather than on a trellis. It needs a long, hot season of about 90 days to reach full size and sweetness. Harvest when the ground spot turns deep yellow and the tendril nearest the fruit browns and dries.
Full growing guide
For planting dates, care, and harvest that apply to all watermelon, see the complete guide.
How to grow WatermelonOther watermelon varieties
Variety characteristics are general guidance for US home gardens; performance varies by climate, soil, and season. Seed and plant availability differs by supplier. Page updated Aug 4, 2026.