Black Diamond Watermelon Care

The black diamond watermelon is not just your ordinary type of fruit. No, it is known for its enormous size, sweet fruit, and juiciness.

These heirloom watermelons are popular to grow for commercial to home growers. The green, black, melon red flesh stands out and lacks the usual stripes found with your traditional watermelon varieties.

Furthermore, it is a late-season watermelon that can weigh up to 50 pounds and is delicious 😋.

Plant Name: Citrullus lanatus Black Diamond

Other Name: Black Diamond Watermelon

Plant Type: Annual fruit

Native Areas: Africa

Light Requirement: Full sun

Watering: Regular watering

Fertilizer: Organic material

Toxicity: Non-toxic

Temperature: Warm temperatures


Growth: 20 feet long vines

Soil Type: Sandy to loamy soil

USDA Hardiness Zones: 3-9

What is a Black Diamond Watermelon?

black watermelon

The black diamond watermelon is an heirloom variety falling under the open-pollinated category. The plant grows on vigorous vine borers to yield a fruit size that weighs up to 50 pounds.

Apart from the weight, the plant develops both male and female flowers and has dark green skin that looks black. Furthermore, the watermelon maintains the same structure and size.

Because of the size, you can expect a long growing season before harvesting the ripe watermelons. It can take up to 90 days when you plant black diamond watermelons to reach maturity.

While this seems like a long wait, it remains rewarding in this watermelon variety as you can enjoy the sweet taste of the pink-red flesh.

It is a classic oblong watermelon 🍉 cultivated in Arkansas in the 1940s to 50s but dates back 5000 years ago in Egypt. Another distinction is that the length of the fruit can reach six feet, with the vines up to 20 feet.

The fruit also has a high water content and is refreshing to add to your diet.

 Watermelon Fruit Nutrition

As with other melons, the black diamond watermelon is equally popular with its hard rinds and crisp, sweet flavor to add to your diet. But one thing is for sure, as with most melons, the black diamond is packed with nutrition:

  • It is low in calories, only 85 calories per 280 grams or about two cups.

  • The fruit has a low carbohydrate of 12 grams per cup or 125 grams

So, with the low-calorie count and the macronutrients, it makes for a great summer snack instead of eating an apple 🍎 or orange.

Furthermore, it is loaded with minerals and vitamins A and C, while the carotenoids and potassium are effective in maintaining a healthy diet for the heart and your cholesterol.

As with most melons, you cannot always enjoy all parts of the fruit but not with the black diamond watermelon.

You can eat from the rind to the flesh for healthy consumption, including the seeds. So, enjoy this light fruit filled with antioxidants to source your cucurbitacin E and vitamin C to help fight cancer and tumors. In contrast, the high levels of vitamin C add more benefits.

Enjoy the enormous-sized watermelon in a salad, eat it straight from the bowl, or add it to a smoothie. You can enjoy the watermelon year-round by pickling the rinds for a healthy treat.

Watermelon Varieties

watermelon varieties

On the market, you can find a variety of watermelons that include the icebox and picnic, suitable to fit into your refrigerator. You can find extra large watermelons, seedless ones, and even yellow-fleshed cultivars. Here we have some varieties you can consider.

All sweet 

This watermelon variety can reach 19 inches long and weigh up to 30 pounds. It has striated green skin with sweet red flesh. It is a picnic watermelon 🍉 suitable for large groups to share.

Blacktail Mountain 

These watermelons weigh 15 pounds and are an excellent choice to enjoy in one sitting. It thrives in cooler environments to enjoy having this sweet treat.

Golden Midget 

The fruit size can fit into your hand and is an excellent choice for one person to enjoy. The bright yellow rind with bright red flesh is sweet, and you can harvest it after planting in 70 days.

Big Tasty and Orange Crisp

These melons are seedless and sweet but are not as big as your heirloom watermelons, reaching only 12 inches. As with the Big Tasty, the Orange crisp is also seedless with a flesh matching the name.

Black Diamond Watermelon Care

The care for the classic oblong watermelon is the same as other melons. So, to grow black diamond watermelons, here are some tips you can follow.

growing watermelon

Growing Tips

Now, if you are wondering how to grow black diamond watermelon varieties, you will need a lot of space in the garden. The vigorous vines alone need a distance of up to 20 feet to sprawl, while the fruit size needs six feet to develop.

Once the watermelon becomes the size, it must rest on the soil to form a tennis ball to prevent rot. To help elevate the watermelon, you can use cardboard or straw. Furthermore, to reach mature size, it needs 90 days to grow compared to others only require 80 days.

So, patience is critical when growing black diamond watermelons. Another thing that makes the black diamond a worthy option is the prolonged hot temperatures to grow. It also attracts bees that help pollinate the whole garden.

The strong rind also resists bruising, and if you end up with more melons than you expected, use it to make cosmetics, soaps, and essential oils.

Light Requirement

Black diamond watermelons need the same light requirements as other varieties, including full sun. Growing strong and healthy requires up to eight hours of sunlight daily.

Soil Needs

potting mix for black diamond watermelon

The important thing with the black diamond watermelon is providing well-draining soil. It also prefers moist conditions and slightly acidic soil.

Temperature and Humidity

The melon prefers warm temperatures and will not thrive in cold temperatures. They prefer moist conditions and grow drier than in a humid place leading to fungal infections.

How to Water Watermelons

watering watermelon

Watermelons need plenty of water to make them juicy. So, keep the soil moist and prevent it from getting soggy. With regular watering, you ensure that your black diamond watermelon remains healthy.

It is crucial to water watermelons at the vines where they root to avoid getting the leaves wet.

Doing this helps prevent fungal problems. Once the melon reaches the tennis ball size, you only need to water it within the soil dries. Stop watering your melons two weeks before they reach maturity to increase the sugar content.

Fertilizing Tomatoes


The black diamond watermelon thrives in rich soil amended with organic material. You can add a lot of compost to the soil. Once the flowers appear, you can apply fertilizer to help encourage melon production.

During the early growing season, you can use a nitrogen-based feed and switch to potassium and phosphorus when flowers appear.

Pruning Black Diamond Watermelon

Pruning Black Diamond Watermelon

Think about the size to give your plants enough space to grow. Hence, pruning is essential; you must do it twice after planting. You can remove the top shoots while keeping up to four branches.

So, count up to five leaves and cut the new shoot using pruners. Doing this helps the black diamond watermelon grow to four new healthy vines.

It also helps to control the vegetation providing more space for those large watermelons. Furthermore, it keeps pests and diseases under control.

When to Harvest Black Diamond Watermelons

Determining the ripeness is a challenge with the black diamond watermelon. So, when picking the ripe melon, it helps to pay attention to the tendril connecting the plant stem to the melon.

The black diamond watermelon is not ripe if you notice a green tendril. But when the tendril becomes dried and brown, it is ripe for the picking.

Other signs are lifting or rolling the watermelon as it is and checking where the watermelon varieties rest on the ground. When a melon is ripe, the rind becomes creamy and hardens once mature.

You can also scratch the rind with your fingernail, and if easy to scratch, it is ripe. Lastly, when you knock against the rind, which sounds hollow, it is another sign that you can enjoy your melon.

Step-by-Step Guide to Grow Black Diamond Watermelons

The best is to start seeds indoors when growing your black diamond watermelon.

watermelon seeds

Steps For Starting Seed Indoors

  1. Sow seeds into biodegradable pots about 1/4 inch deep to lightly cover with a starting mix. It will make it easier to transplant them when the soil temperature warms up.

  2. Keep soil moist and warm as the seeds germinate better, and keep temperatures around 70°F and higher.

  3. Once seeds germinate and you notice seedlings emerge, please cut back on watering when the seedlings have leaves and reduce watering again.

  4. Keeping the soil warm speeds up germination, and when temperatures rise after the last frost, you can use a hardening-off process before you transfer the seedlings into the garden

You can sow seeds directly into the garden if you live in a region with hot temperatures throughout the growing season.

Direct Sowing Black Diamond Watermelon Seed

  1. After the last frost, you can sow seeds in moist, well-draining soil.

  2. Cover the seeds with the soil and apply a mounding method to press up to five seeds an inch into the ground.

  3. Once seedlings emerge, you can thin them out to two or three plants.

  4. For the recommended spacing needs, check your seed packet.

  5. Provide seedlings with full sun and keep the soil moist.

Common Pests and Diseases

tomatoe pests

As with any plant, your black diamond watermelon can become bothered with common pests that include:

For most pests, it helps to introduce predatory wasps into the garden. For diseases, the diamond watermelon can get downy mildew, Alternaria leaf spot, stem blight, and other fungal diseases.

Frequently Asked Questions

You can save the seeds to grow another batch of black diamond watermelon. You scoop out the seeds and place them on a wire mesh sieve. Then run the seeds under water and rub them against the mesh to remove the fibers.

Place the seeds in a bowl with clean water and stir them. Remove the seeds that float to discard them. Drain the water and place the black diamond watermelon seeds on a baking pan lined with wax paper. Leave them to dry in a warm spot and keep stirring to expose them to fresh air.

You can return the seeds indoors after a day and let them dry inside for a week or two. Store the seed in tight containers in a dry place.

The health benefits of diamond watermelon are many. It has a 92% higher water content and will provide the required water intake. It is high in magnesium, potassium, and all the vitamins your body needs daily.

The black diamond watermelons are self-pollinating as the seeds are fertile and pollinate the vine when producing flowers. The flowers resemble squash flowers, and you can plant herbs with your watermelon to attract bees and more.

These are picnic watermelons with a round or oval shape, bright green outside, and bright red sweet yet juicy inside.

The first notable difference when looking at the black diamond watermelon is the size and weight, weighing up to 50 pounds. The black diamond watermelon has a sweeter taste with a higher water content. Neither does the rind have the strips you are used to.

The best is to examine the leaves, stem, and tendrils. You can pick the black diamond watermelon when the stem and tendrils are brown and dried. Also, do not pick it when green; it should have a hollow sound.

Whether you want to buy, sell, or simply reach out to other plant enthusiasts, Plantly is the right place to be!

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