The Black Diamond is a classic heirloom watermelon cultivar, prized for its impressive size and flavor. This open-pollinated variety, developed in the 1940s, is easily recognizable by its deep, dark green rind, which can appear almost black, contrasting sharply with its bright, sweet, cherry-red flesh. It has been a favorite among gardeners and commercial growers.
Expected Size Range
The Black Diamond watermelon is classified as a giant variety, with typical mature fruits weighing between 30 and 50 pounds. Under standard growing conditions, a melon of this size is a common expectation. These large, slightly oblong fruits often measure around 12 to 14 inches across their widest point.
The maximum potential size is substantially larger than the average harvest; growers have reported watermelons reaching up to 75 pounds. In rare instances, weights approaching 100 pounds have been noted. Achieving this maximum size requires an extended season and carefully controlled environmental inputs.
Key Factors Influencing Growth and Size
Nutrient Requirements
To achieve the upper end of the Black Diamond’s size potential, the vine requires an abundance of resources. Watermelons are heavy feeders and need soil rich in organic matter and nutrients to support large fruit development. Preparing the planting site with plenty of compost or a balanced fertilizer application is beneficial for establishing a strong root system.
Water Management
Consistent and plentiful moisture is another determinant of final fruit size, especially during rapid fruit expansion. The plant’s extensive root system needs deep watering to prevent stress, which can halt growth and reduce the melon’s weight. Watering must be tapered or stopped entirely about two weeks before harvest to concentrate the sugars and enhance sweetness.
Spacing and Sunlight
Space allocation is equally important for this sprawling vine, which can reach up to 15 to 20 feet in length. Black Diamond plants should be spaced at least four to six feet apart to give each vine sufficient room to spread and capture sunlight. This generous spacing ensures that the large leaves, which help prevent sun-scald, can fully develop and support the energy demands of a large melon. Any restriction in growth area or lack of full sun exposure will negatively impact the plant’s ability to produce its largest fruit.
Time to Maturity and Harvest Indicators
The Black Diamond variety is a late-season melon, requiring about 80 to 100 days from planting until maturity. This means the plants need warm temperatures and a reliably long summer to complete their growth cycle. The 90-day mark is often cited as the average time for the fruit to reach its full size and peak sweetness.
A grower knows the melon is ready for harvest by observing specific physical indicators. The pale spot where the watermelon rests on the ground, known as the ground spot, changes from white or light green to a creamy yellow color as the melon ripens. This color change signals that the fruit has accumulated its maximum sugar content.
A second reliable indicator is the condition of the tendril closest to the fruit stem. This small, curly vine structure will dry up and turn brown when the melon is mature. If the tendril remains green, the melon is still developing and should be left on the vine to continue increasing in size and sweetness.