30 seeds. 85 days. Citrullus lanatus. Annual.
 
Watermelon 'Black Diamond' has dark green skin with juicy red flesh. The hard skin makes it good for shipping and storing. It weighs around 35 to 40 pounds. Open-pollinated.
 
Sowing Watermelon Seeds: 
 
Sow seeds outdoors after the last frost date when the soil is warm, 1/2 inch deep. Sow in hills that are spaced 5 feet apart and thin to 3 plants per hill, or sow in rows 2 feet apart. Full sun.