How to Grow Black Diamond Watermelon
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Black Diamond Watermelon
Citrullus lanatus
vegetableBlack Diamond is a large, round watermelon variety with a dark green to nearly black rind and sweet, deep red flesh. This heirloom variety produces impressive fruits weighing 15-25 pounds and is prized for its excellent flavor and impressive appearance. It's a heat-loving annual vine that thrives in warm climates.
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Example Black Diamond Watermelon timeline · Pittsburgh, PA (Zone 6b)
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Plant Black Diamond Watermelon
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Black Diamond Watermelon
Around Jul 1≈ 75 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Black Diamond Watermelon dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 3-10 when planted in warm season; requires warm soil (70°F+) and frost-free conditions
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Get my Black Diamond Watermelon timeline →Growth Stages
Seedling
10-14 daysCotyledons emerge with first true leaves developing; plant remains small with 2-4 true leaves visible
Keep soil consistently moist but not waterlogged; provide full sun; thin seedlings if overcrowded
Vegetative Growth
3-4 weeksVigorous vine production with multiple long runners; leaves grow larger and more abundant; no flowers yet
Water deeply and regularly; provide consistent nitrogen; mulch around plants to retain moisture and suppress weeds; begin trellising if space is limited
Flowering
2-3 weeksYellow flowers appear on the vines; male flowers emerge first followed by female flowers (identifiable by small immature fruit behind the flower)
Ensure adequate pollinator access; reduce nitrogen fertilizer to encourage fruiting; continue consistent watering
Fruit Development
4-5 weeksSmall watermelons form and rapidly enlarge; vines sprawl extensively; fruits develop characteristic dark green to black coloring
Water deeply at least 1-2 times weekly; place straw under developing fruits to prevent rot; thin excessive fruits (keep 1-2 per plant for larger melons); reduce overhead watering to minimize disease
Ripening & Harvest
1-2 weeks until readyFruits reach full size and develop deep coloring; bottom spot yellows; tendrils near fruit stem dry and brown
Reduce watering slightly to concentrate sugars; check for ripeness using the thump test, weight, and appearance; harvest when ripe to prevent splitting
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Use row covers on young plants; handpick; spray with neem oil or insecticidal soap; plant nasturtiums as trap crop
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Wrap base of vine stems with foil; inject Bt into stems; plant early to avoid peak laying season; remove affected vines promptly
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Spray with strong water stream; use insecticidal soap; apply neem oil; attract beneficial insects like ladybugs
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Increase humidity; spray with water; use miticide if needed; ensure adequate moisture to discourage infestation
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Improve air circulation; avoid overhead watering; apply sulfur dust or baking soda spray; remove affected leaves
Uses
Fresh fruit consumption
CulinaryBlack Diamond watermelons are primarily enjoyed fresh, sliced and eaten as a refreshing dessert fruit. The sweet, crisp red flesh makes them ideal for summer eating, fruit salads, and cold beverages. [source]
Juice and beverages
CulinaryThe fruit can be juiced to make refreshing watermelon juice or blended into smoothies and frozen desserts. Seeds can be roasted and eaten as a nutritious snack. [source]
Hydration and wellness
MedicinalWatermelons are 92% water and contain citrulline, an amino acid that may support cardiovascular health and blood flow. Traditionally used in various cultures for rehydration and summer cooling. [source]
Compost material
HouseholdSpent vines, seeds, and non-salable fruits can be composted to improve soil structure and nutrient content for future plantings. [source]
Wildlife food source
WildlifeWatermelon flowers attract pollinators like bees and butterflies. Fallen or split fruits provide food for beneficial insects and wildlife in permaculture systems. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Harvest when the bottom spot turns creamy yellow, the melon sounds hollow when thumped, and the tendril nearest the fruit stem browns and dries. Fruits typically reach 15-25 pounds at full maturity. Cut the stem with a sharp knife rather than pulling. Store at room temperature for 1-3 weeks or refrigerate for up to 3 weeks. Peak flavor is at room temperature.
Fun Facts
- 🌱 Black Diamond watermelons were historically popular in the Southern United States and are experiencing a resurgence as gardeners rediscover heirloom varieties with superior flavor compared to modern commercial hybrids.
- 🌱 The dark coloring of the Black Diamond rind comes from high levels of anthocyanins and chlorophyll, which help the fruit absorb more solar heat and ripen faster than lighter-colored varieties.
- 🌱 A single Black Diamond plant can produce 2-3 large melons in optimal conditions, though reducing to 1-2 fruits per plant directs all plant energy into producing exceptionally large, sweet melons.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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