Black Diamond, Heirloom Watermelon Seeds

Black Diamond, Heirloom Watermelon Seeds — The 1950s Giant Classic With Dark Blue-Black Rind, Bright Red Flesh, and a Built-In Yellow Belly Ripeness Indicator, 30–50 lbs

Black Diamond (Citrullus lanatus) is one of the great heirloom watermelons of the American garden — a classic oblong giant with a strikingly dark blue-black rind covered in prominent creases, crisp bright red flesh, and a built-in ripeness signal that home gardeners have relied on for generations. As the melon ripens, the underside where it rests on the ground turns from white to a rich yellow — the iconic “yellow belly” that tells you harvest time has arrived. Fruits grow large, often 30–50 lbs and 19×17 inches, with a tough rind that stores and ships exceptionally well. Bright red, sweet, and satisfying — a summer watermelon that delivers everything you want. 90–95 days.

Why Grow Black Diamond?

• 30–50 lb oblong giants — dark blue-black rind with prominent creases, dramatic and beautiful
• Built-in yellow belly ripeness indicator — no guessing when to harvest
• Bright red, crisp, sweet flesh — classic summer watermelon flavor
• Tough rind stores and ships exceptionally well — great for markets and extended home use
• Heat tolerant — thrives in hot summer conditions
• Classic seeded variety — perfect for seed-spitting contests and seed saving
• Open-pollinated heirloom — save seed year after year

Knowing When to Harvest

Black Diamond’s “yellow belly” is your primary ripeness cue — the spot where the melon rests on the soil turns from creamy white to rich golden-yellow when fully ripe. Confirm ripeness by checking the tendril closest to the fruit stem: when it has dried and turned brown and curled, the melon is ready. The rind will also dull from shiny to matte. Thumping should produce a deep, hollow thud. Do not rely on size alone — wait for the yellow belly and dried tendril together for peak sweetness.

In the Kitchen

Slice chilled for classic summer eating. Cube into fruit salads and salsas. Blend into agua fresca or watermelon lemonade. Grill thick slices briefly for a caramelized summer side. The large seeded fruits make for classic backyard seed-spitting fun. Scoop the flesh and freeze in cubes for smoothies and cocktails all summer long.

Growing Notes

Direct sow ½–1 inch deep outdoors after last frost when soil has warmed to at least 70°F, or start indoors 3–4 weeks before transplanting. Space plants 30–60 inches apart in rows 7–10 feet apart — Black Diamond needs ample room to sprawl. Full sun. Fertile, well-draining soil. Keep consistently moist during fruit development. Black plastic mulch warms soil and conserves moisture. Avoid overhead watering. Feed with a balanced fertilizer at planting; switch to low-nitrogen once vines run. One plant can produce 2–3 giant melons in a season.

Packed and shipped by Box Garden Seeds LLC — heirloom seeds grown without GMOs, selected for flavor, resilience, and your garden’s success.