Citrullus lanatus 'Black Diamond'
fruitBlack Diamond is a heritage round watermelon from the 1950s known for its near-black rind and impressive size - 35 to 50 lb fruits with thick, bruise-resistant skin and bright red, crisp, very sweet flesh. Long widely grown in the American South as a roadside-stand variety, it remains a favorite for gardeners who want the classic giant picnic melon and have the space for sprawling vines.
Sun
full sun
Water
Every 3 days
Harvest
~90 days
Difficulty
medium
Lifecycle
annual
One season, then done
Spacing
36 in. apart in hills
Planting Depth
Seed 1 in. deep
Soil pH
6.0-7.0
Soil Type
Rich, well-draining
Hardiness Zones
Zones 3 – 11
Grown as an annual. This range is its winter hardiness, but you can grow it for a single season in any zone.
When to Fertilize
At planting, at vining, and at fruit set
Fertilizer
10-10-10 pre-plant; lower N during fruit set
Black Diamond needs heat and space. Direct sow after the soil reaches 70F or start indoors 2 to 3 weeks before transplanting in peat or paper pots. Plant 4 to 5 seeds per hill at 1 inch deep and thin to 2 or 3 strongest plants; space hills 3 ft apart in rows 6 to 8 ft apart. Use black plastic mulch and drip irrigation in cooler regions for best yields. Side-dress with balanced fertilizer at vining and again at fruit set, then taper water as fruits approach maturity to concentrate sugar.
Start seeds indoors
Mar 25
Transplant outdoors
Apr 29
Projected first harvest
Jul 28
Good neighbors that attract beneficial insects or deter pests
Proactive ways to stop trouble before it starts. Tap a name with an arrow for its full guide
Cover transplants with floating row cover until flowering, then remove for pollination
Inspect leaf undersides for copper egg clusters and crush; trap adults under boards
Plant alyssum to draw hoverflies, support ladybugs, and hose off colonies
Rotate watermelons every 3 to 4 years and remove infected debris at season end
A ripe Black Diamond shows three signs: the tendril nearest the stem has dried and browned, the ground spot has turned creamy yellow, and a thump sounds dull and deep. With fruits this large, cradle the melon and cut the stem with shears, leaving an inch attached. Whole melons hold a week at room temperature; refrigerate only after slicing.
Watermelon delivers around 4.5 mg of lycopene per 100 g, more than fresh tomato, plus useful vitamin C, vitamin A as beta-carotene, and potassium. At 92 percent water and about 30 calories per 100 g, it is one of the most hydrating fruits in the garden, and the citrulline in the rind has been shown to support blood vessel health.
For educational and informational purposes only. HomeSown is not medical, health, or other professional advice. Always positively identify any plant before handling or eating it; some plants, and some parts of otherwise-edible plants, are toxic. Consult a qualified professional before consuming or otherwise using any plant, especially if you are pregnant, nursing, taking medication, or have a health condition.