Growing black diamond watermelon

Black Diamond Melon Care: Growing Black Diamond Watermelons

There are many key aspects that gardeners take into consideration when deciding which varieties of watermelon to grow in their gardens each season. Characteristics such as days to maturity, disease resistance, and eating quality are paramount. Another very important aspect, however, is size. For some growers, choosing varieties which produce large melons is non-negotiable. Learn some Black Diamond watermelon info in this article.

What is a Black Diamond Watermelon?

Black Diamond is an heirloom, open-pollinated variety of watermelon. For generations, Black Diamond watermelons have been a popular choice for both commercial and home growers for many reasons. Black Diamond watermelon plants produce vigorous vines, which often yield fruits weighing in excess of 50 lbs. (23 kg.).

Due to the large size of fruits, gardeners can expect this plant to require a long growing season in order to harvest fully ripe melons. Mature melons have very hard rinds and sweet, pink-red flesh.

Growing Black Diamond Watermelons

Growing Black Diamond watermelon plants is very similar to growing other varieties. Since all watermelon plants thrive in sunny locations, at least 6-8 hours of sun each day is imperative. Additionally, those wishing to plant Black Diamond will need to ensure a long growing season, as this variety may take at least 90 days to reach maturity.

To germinate watermelon seeds, soil temperatures of at least 70 F. (21 C.) are required. Most commonly, seeds are direct sown into the garden after all chance of frost has passed. Gardeners with shorter growing seasons attempting to grow Black Diamond watermelons may need to start seeds indoors in biodegradable pots before transplanting outside.

Harvesting Black Diamond Watermelons

As with any variety of watermelon, determining when fruits are at peak ripeness may be somewhat of a challenge. When attempting to pick a ripe watermelon, pay close attention to the tendril located where the melon connects to the plant stem. If this tendril is still green, the melon is not ripe. If the tendril has dried and turned brown, the melon is ripe or has started to ripen.

Before picking the watermelon, look for other signs that the fruit is ready. To further check the progress of the watermelon, carefully lift or roll it. Look for the place in which it was resting on the ground. When the melon is ripe, this area of the rind will usually have a cream-colored appearance.

Black Diamond watermelon rinds will also harden when they are ripe. Try scratching the watermelon rind with a fingernail. Ripe melons should not be able to be easily scratched. Using a combination of these methods when picking watermelons will ensure a much higher likelihood of choosing a fresh, juicy fruit that is ready to eat.

How to Grow Black Diamond Watermelon | Guide to Growing Black Diamond Watermelon

Seeds or Seedlings

3 to 5 days, 60F to 95F

4 years

High Fertility

Full Sun

12″ apart

4′ to 6′ apart

65 to 86

Growing Guide

Indoor Starting
As they require a long growing season, watermelons are best started indoors approximately 3-4 weeks prior to the last frost of the season. Sow seeds 1/4″ deep in flats or small pots, sowing 3 seeds per pot. Keep medium moist while awaiting germination. Additionally, watermelon seeds will show better germination rates with heat. Keep the soil between 80-90 degrees, using a heat mat if necessary. Seed should begin to germinate within 3-10 days.

Once seeds start to germinate, lower soil temp slightly to the mid 70s, for 1-2 weeks, also decreasing water. Thin to one plant per cell or pot. Once the first set of true leaves has developed, reduce waterings once more, but do not allow plant to become desiccated.

Harden plant by gradually exposing to outdoor conditions. Transplant to permanent site in late spring after the last frost has passed. If possible, transplant on an overcast day to minimize wilting and create a more amenable environment for your young plant.

Outdoor Starting
If you have long, hot growing seasons, melons can direct-seed into garden. To ensure ripening in areas with shorter growing seasons and cooler weather, choose fast-maturing varieties, start plants inside, use black or IRT plastic mulch to warm soil and use fabric row covers to protect plants.

Direct-seed 1 to 2 weeks after average last frost when soil is 70 F or warmer. Plant 1 inch deep, 6 seeds per hill, hills 4 to 6 feet apart; or 1 foot apart in rows 5 feet apart. Can plant at closer spacings if trellised. Thin to 2 to 3 plants per hill.

Choosing a Site
Prefers warm, well-drained, soil, high in organic matter with pH 6.5 to 7.5. Consistent, plentiful moisture needed until fruit is about the size of a tennis ball. Soil temperatures below 50 F slow growth. Consider using black plastic and fabric row covers to speed soil warming. Sandy or light-textured soils that warm quickly in spring are best.

In many areas, successful crops require starting plants indoors, using plastic mulch to warm soil, and fabric row covers to protect young transplants.


For transplanting, sow seeds indoors ¼ inch deep in peat pots (2-inch square or bigger), 2 to 4 weeks before setting out. Plants should have one or two true leaves when transplanted.

Transplant at same spacings as direct-seeded crops – 2 to 3 plants per hill in hills spaced 4 to 6 feet apart, or 1 to 2 feet apart in rows 5 feet apart. Transplants are delicate and roots are sensitive to disturbance. If you need to thin, use scissors. Keep soil intact around plant when transplanting.

Mulch plants after soil has warmed to help maintain consistent moisture and suppress weeds.

If using fabric row covers, remove at flowering to allow pollination by bees. Good pollination is critical to fruit set.

Plants require consistent moisture until pollination. Once fruits are about the size of a tennis ball, only water if soil is dry and leaves show signs of wilting.

To prevent insect damage to developing fruits, place melons on pots or pieces of wood.

If growing melons on a trellis, support fruit with slings made from netting, fabric, or pantyhose. Trellising improves air circulation around plants and can help reduce foliar disease problems. Choose small-fruited varieties and reduce plant spacing.

For large plantings, leave a strip of rye cover crop every second or third row perpendicular to prevailing winds to protect plants from damaging wind.

To reduce insect and disease problems, avoid planting cucumber family crops (melons, squash, pumpkins) in the same spot two years in a row.

Do not let your melon plants get dried out during the growing season. They are not tolerant of drought. Additionally, be cautious not to over-water plants as this can negatively impact the taste and flavor later on. Keep soil moist but not soggy.

Organic Black Diamond Watermelon Seeds

Organic Black Diamond Watermelon Seeds Citrullus lanatus King of the Garden Watermelon, Black Beauty Watermelon, Shadow Melon Description: Black Diamond is a classic oblong watermelon with a black-green rind covering bright red, crisp, flavorful flesh. In the 1950s, Black Diamond was a very popular home garden variety. Fruits have gray-black seeds (Perfect for seed spitting contests, if that is your desire!) and can grow quite large, often topping 45 or more pounds. Days to Maturity: 75-80 Days Fruit: The flesh is bright red and mouthwatering sweet and the skin is decidedly dark green in color, very striking when plated. Fruit Size: Up to 20-24 inches in length, 12-14 inches in diameter, normally 25+ pounds, but may grow as big as 40-50 pounds. Fruit Color: Dark green skin with brightred flesh, very sweet. USDA Zones: 2b – 11b (At elevation Zones 3b – 11b) Life: Annual Soil: Loose, loamy, amended with compost, slightly sandy. The better the soil, the better the Watermelon. Mulching with dark/black material to cover the soil will serve multiple purposes: it will warm the soil, hinder weed growth and keep developing fruits clean. Soil pH: 6.0 to 6.8 Sun: Full sun, no shade. Sowing: If you live in warmer climes, you can direct sow seeds outdoors, but wait until the soil temperature warms to at least 70 degrees F to avoid poor germination and losses. Watermelon vines are exceptionally tender and should not be transplanted until all danger of frost has passed

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