A Basic Guide to Growing the Not-So-Basic Black Diamond Watermelon

slices of watermelons
  • Black diamond heirloom watermelons can grow to an impressive 50 pounds or more and reach lengths of 6 feet.
  • There are several health benefits to the black diamond watermelon. They are rich in minerals and vitamins, have anti-inflammatory properties, and are great for weight management.
  • Garlic, radish, marigolds and broccoli are the best companion plants to deter pests and encourage pollination. 
  • Don’t plant tomatoes, peppers, and potatoes near the black diamond watermelon because they are harmful and bring dangerous aphids.

Whether you are a  seasoned horticulturist or venturing into garden care for beginners, the black diamond watermelon is the ultimate choice for a large, sweet fruit to add to your garden. Unless you live in the south, you may have never seen or even heard of these watermelons. Or, perhaps you’ve only used them for a greased watermelon throwing contest (yes, that’s a thing). 

But it’s time to try something new which is sure to impress everyone. Although the black diamond watermelon may seem like an exotic choice for your garden, it’s easier to grow than you may think. If you have a bit of space, good access to water and your region has 6-8 hours of sunlight for a 90-day period, this watermelon is 100% feasible for you to grow. Read our comprehensive guide and get started!

The black diamond watermelon is sometimes described as the “king” of the garden. Weighing more than 50 pounds (or more), this classic oblong watermelon is known for its enormous size, as well as its bright red, crisp and delicious flesh. Unlike other watermelons, this black watermelon lacks the typical stripes, which makes them more unique.

The black diamond watermelon is also the quintessential watermelon of the summer season. It is equally popular with both commercial and home growers. If you’re interested in growing this variety of watermelon and want to grow your garden, here’s everything you need to know.

What is a Black Diamond Watermelon?

Black diamond watermelons (scientific name: Citrullus lanatus) are considered heirloom watermelons that fall under the open-pollinated category. This black watermelon can produce vigorous vines and yield fruits that weigh more than 23 kilograms.

Apart from its heavyweight, this watermelon variety sets itself apart from other melons with its black-green peel and seeds (which are either black or gray; they also maintain the same size and structure).

Because of its large size, expect this watermelon variety to have a long growing season before you can harvest fully ripe watermelons. It takes 80 to 90 days for your black diamond watermelon to grow to full size. It seems like a long wait, but once the melons have matured, you’ll be rewarded with hard rinds and delicious, pink-red flesh.

Black Diamond Watermelon History

If you live in the southern states of America, you may have seen this gigantic melon with dark skin in your local market. Maybe you recognized it as a watermelon but without the characteristic stripes. Maybe you have even tried it and been enraptured by its sweet crispy flesh. Or perhaps you are wondering, ‘What is a black diamond watermelon?’ 

These large, sweet beauties were originally developed in Arkansas in the 1940s and hit markets in the 50s. Although the black diamond watermelon origin makes it an heirloom, many people are still unfamiliar with this fruit. 

The cultivation of regular watermelons was first recorded over 5000 years ago in Egypt. We love this summer fruit that is a quintessential. But what does a black diamond watermelon look like, and how does a black diamond watermelon taste? 

The black diamond watermelon size is its most distinctive quality. Their length can reach up to 6 feet and weigh 50 pounds. The vines can reach 20 feet. They have lovely black-green skin and are oblong in shape. Their flesh is bright red, and these watermelons have a sweet, crisp flavor. The black diamond watermelon has a very high water content due to its immense size, making it a refreshing choice to add to your garden and your diet! 

Black Diamond Watermelon Nutritional Information

Watermelons are a healthy choice in any diet, and the black diamond watermelon is amongst the best choices. It has a low number of calories, or only 85 calories per 280 grams, or about two cups. It is also a low source of carbohydrates – just 12 grams per cup (or 152 grams). The low-calorie count and macronutrient content make it a better choice than an apple or orange. 

The black diamond watermelon fruit is loaded with vitamins and minerals. You can expect to get high amounts of vitamins A and C. The carotenoids and potassium levels are especially effective in maintaining a healthy heart and reducing cholesterol. Every part of the black diamond watermelon is edible and healthy for consumption – from the rind to the flesh and seeds!

If you are looking for a light fruit with plenty of antioxidants, this watermelon has you covered. It’s a great source of lycopene and cucurbitacin E, which are effective in preventing tumors and cancer. The high levels of vitamin C give you added antioxidant benefits. Enjoy a salad, smoothie loaded with watermelon, or eat them straight out of a bowl. Add black diamond watermelons to your diet year-long by pickling the rinds for a healthy and delicious treat.

Know About Other Popular Watermelon Varieties

The main kinds of watermelons on the market include a picnic, icebox (meaning they are the perfect size for your fridge), individual-sized, extra large, seedless, and yellow-fleshed. With so many varieties of melon, there is sure to be a crowd-pleasing favorite for every occasion. Choose the watermelon which is ideal for your lifestyle. 


The Allsweet will grow to about 17-19 inches long and weigh 25-30 pounds. It has that characteristically striated green skin and sweet red flesh. Its size makes it typical for picnics, as there will be plenty to share with a larger group.  

Blacktail Mountain 

Blacktail Mountain is 6-15 pounds making it a good choice if you don’t plan to eat it all in one sitting. This watermelon is also suited for growing in cooler environments where it cools down at night.

Golden Midget 

An example of a personal-sized melon might be a Golden Midget. It can fit in the palm of your hand, making it a good choice for one person. It has a bright yellow rind and pink flesh, and its small size means a quicker harvest – about 70 days. 

Big Tasty and Orange Crisp

The Big Tasty is sweet and seedless. But at 10-12 inches, it’s not nearly as big as our  black diamond heirloom watermelon. Orange crisp has a flesh to match its name, a bright orange, and an intoxicating aroma.

Black Diamond Watermelon Care

Despite its drastic difference from other watermelon varieties, growing black diamond watermelons is similar to other types. To grow your own black diamond watermelon patch, here are the basics every gardener should know.

Watermelon vs. Black Diamond Watermelon

The black diamond watermelon size may be the first difference you notice when comparing it to its watermelon counterparts. Weighing in at 50 pounds, it is more than twice the size of your traditional picnic-style watermelon. 

It has a delicious sweet taste which is very mild since it has a higher water content than most watermelons – 92%. That high water content will also produce a very crisp fruit. You may be accustomed to the striated rind of your average supermarket watermelon, but the black diamond watermelon does not have the familiar strips.

Growing Requirements

If you are wondering how to grow a black diamond watermelon, you need to allow for more space. The sprawling vines will need 20 feet, and of course, the fruit will need 4-6 feet. They need to rest above the soil once they become the size of a tennis ball to prevent rot. You can use a patch of straw or even some cardboard to elevate it.

In order for these jumbo watermelons to reach their full potential, they need 90 days to grow. Most watermelons require 60-80 days to reach maturity. So be patient and wait a while.

Growing black diamond watermelon is especially advantageous due to its size. They are also a good choice for late in the season as they need those long, hot days. It attracts lots of bees. More bees mean more pollination for your entire garden. The rind is especially strong and resists bruising. And if you have more melon than you know what to do with, consider using it to make essential oils, cosmetics, and soaps!

How Much Light Do Black Diamond Watermelons Need?

Like other watermelons, the black diamond variety needs plenty of sunshine. They require at least six to eight hours of sunlight every day to keep the melons growing strong and healthy.

What Should the Temperature and Humidity Levels Be?

watermelon cut in half
Photo by aung nyi on Unsplash

These black watermelons are big fans of hot temperatures and do not thrive in cold temperatures. They prefer moist conditions. However, growing your watermelons in a very humid place might trigger fungal infections.

How Much Water Does a Black Diamond Watermelon Need?

Watermelons are known for being juicy, so it makes sense that they need plenty of water. A rule of thumb when it comes to watering your melons: keep the soil moist, but avoid getting it soggy. Regular watering ensures the healthy growth of your black watermelon.

When it comes to watering your melons, water the vines where they are rooted and avoid getting the leaves wet to avoid fungal problems. Once your watermelons have reached the size of a tennis ball, water them only when the soil starts drying out. Two weeks before the melon reaches maturity, stop watering them to increase the fruit’s sugar content.

What Type of Fertilizer Do I Use for Black Diamond Watermelons?

Black diamond watermelons thrive in rich soil and any organic material. Give them the nutrients they need by amending the soil with plenty of compost. You can also apply fertilizer when the flowers appear. This encourages the healthy production of fruits.

During the early growing stages, use a nitrogen-based fertilizer for your black diamond watermelon. Switch to potassium and phosphorus-based fertilizers once the melons produce flowers.

What are the Common Pests and Diseases to Watch Out For?

When growing your black diamond watermelons, look out for common pests, which include squash bags, cucumber beetles, squash vine borers and melon aphids. Alternaria leaf spot, downy mildew, stem blight and other fungal diseases can attack your plants.

Growing Black Diamond Watermelons: Step by Step

These watermelons take their sweet time to ripen, so it’s best to start your seeds indoors for a month. Here’s how:

  1. Plant your seeds 1/4 inch deep into the soil and lightly cover them with starting mix.
  2. Always keep the soil warm and moist since the seeds germinate better in these conditions. Maintain a temperature of 70 degrees Fahrenheit (or higher).
  3. Once the seedlings appear, cut back on watering. When the seedlings grow leaves, reduce the watering again.
  4. Once the temperatures start to rise, begin the hardening-off process until you can plant the seedlings into the garden.

If you live in a place with high temperatures or warm growing seasons, you can directly plant the melons into your garden. Just follow these steps:

  1. After the last frost, plant your seeds in moist, rich and well-draining soil. Cover the seeds with soil.
  2. Apply the mounding method. Create a mound of soil and press three to five seeds about an inch into it. Once seedlings emerge, thin to two or three plants.
  3. Check the seed packet for spacing instructions.
  4. Keep the soil moist.

Pruning Black Diamond Watermelon

When considering how to grow a black diamond watermelon, always think about the space their size will require. That’s why you must prune your plant. You will need to prune your watermelon twice after you plant it. Remove the top shoots and keep three of four branches. While checking your plant, count four to five leaves and then cut the new shoots with something sharp. This way the plant will develop three or four healthy vines. Controlling your vegetation will not only allow more space for the large fruit to develop, but it will allow you to check for signs of pests, disease or deficiency. 

Black Diamond Watermelon Companion Plants

Black diamond watermelon growing is best done with friends – consider companion plants for your watermelon! Companion planting is a great way to deter unwanted pests and increase pollination in your watermelon patch. It is also healthier for the soil.

To reduce pests such as aphids and cucumber beetles (your primary enemies for your black diamond watermelon), you can plant garlic, radishes, broccoli, marigolds, and various herbs. Catnip, dill, mint, and nasturtiums are also helpful to dissuade pests, and they have the added benefit of growing to a smaller stature so they will not steal the sunlight from the black diamond watermelon plant. 

Try corn, broccoli, radishes, marigolds, and tansies to lure away aphids from your watermelons. Cucumbers, squash, zucchini, and pumpkins will draw the cucumber beetles away. Lavender and borage are good herbs for increasing pollination.

The plants to avoid are potatoes, tomatoes, and peppers. These will bring dangerous aphids closer to your watermelon. Other harmful plants would be roses, sunflowers, and aster. 

You should avoid planting the watermelons on the same ground on which you planted squash the previous year.

Harvesting Your Black Diamond Watermelon

Similar to other watermelon varieties, determining when the melons are at with their ripeness can be challenging.

When it comes to picking a ripe black diamond watermelon, pay attention to the tendril that connects the melon to its plant stem. If the tendril is green, your black diamond watermelon isn’t ripe yet. On the other hand, if the tendril is brown and dried, your watermelon is ripe.

Before you harvest your watermelons, look for other signs that the fruit is ready. Rolling or lifting the watermelon always works. Also, check the place where the melon rests on the ground. If the melon is ripe, the area of the rind will be cream in color.

Once they are ripe, the rinds of a black diamond watermelon will harden. Check this by scratching the melon’s rind with your fingernail. If you can easily scratch the surface, the watermelon is ripe.

How to Save Black Watermelon Seeds

If you enjoyed growing black watermelons or wish to grow another batch of them, save the seeds!

To do so, just scoop out seeds from a ripe black watermelon and place them into a wire mesh sieve. Run the seeds over water and rub them gently against the mesh to remove the stringy fibers. Next, place the clean seeds in a bowl of water and stir. You’ll notice that some of the seeds float to the top of the water. This means they are sterile or immature black watermelon seeds. Discard of these.

Stir the water a few more times until there are no more immature seeds. Drain the water from the remaining seeds and place them on a baking pan or heavy plate lined with waxed paper. Let them air dry in a sunny spot.

Stir the seeds on the pan for the next few hours to ensure all of them are exposed to fresh air. After a day, bring the seeds back inside and let them dry for another week or two. Make sure they are dry before you package them for storage. 

If you love watermelon but want something different, grow a black diamond watermelon! It takes a while, but the fruits are worth it.

Health Benefits Of Eating Black Diamond Watermelon

The health benefits of black diamond watermelon are many. There is no other watermelon that can compete with the 92% high water content of this fruit. Drinking enough water on a daily basis is challenging for many people. Your daily water allotment can be supplemented by eating foods rich in water, such as watermelon. Consuming enough water is important in aiding weight loss, keeping skin supple, and proper functioning of organs.

Source of Vitamins and Minerals

The high magnesium and potassium levels are good for reducing your blood sugar levels. It contains arginine, which is beneficial for those with diabetes. Black diamond watermelon is rich in vitamin C and B – C is excellent for glowing skin. The vitamin A and beta carotene content will help your eyesight. 

Don’t limit yourself to the watermelon’s flesh. The black diamond watermelon seed has protein, healthy fats, vitamin B, and minerals as well! Eat them directly from the watermelon or collect them and eat them roasted. This is an heirloom plant, so there isn’t a black diamond watermelon seedless option, but you’ll be glad for their presence.

Antioxidant Properties

The antioxidant and anti-inflammatory properties of watermelon can fight heart disease and bad cholesterol in the form of lycopene. Pickle the rind or saute it, and you’ll have the benefit of citrulline and arginine, which make them excellent for your heart, circulation, and immune system.

Helps with Weight Management

Watermelon is great for your diet when managing your weight. They are high in water and fiber. Eat a bowl of watermelon before a meal to feel fuller. Or indulge in the delicious sweet treat as a perfect dessert. The black diamond watermelon is the perfect selection for every healthy diet as they boast significant health benefits for your entire body.


1) Are black diamond watermelons self-pollinating?

Yes, they are self-pollinating. The seeds themselves are fertile and will pollinate the vine with the flowers the plant produces. They are yellow in color and resemble squash flowers. Plant herbs adjacent to your watermelons to attract those pollinators in your area.

2) When is the right time to pluck a black diamond watermelon?

If you want to know how to tell if black diamond watermelon is ripe, you need to examine the leaves, tendrils, and stem. The tendril and stem will become dried out and brown. Don’t pick the watermelon if it is green. Also, it should have a hollow sound when you give it a thump.

3) Why are Black Diamond watermelons so expensive?

Black diamond watermelon price is higher due to their immense size. Since they take longer to grow, they need maintenance and plenty of water. They take up more space than your average watermelon, thus decreasing the yield. 

4) How big do black diamond watermelons grow?

Growing black diamond watermelon will produce a melon of about 50 pounds and 4-6 feet long. Sometimes they can grow as big as 100 pounds. The largest black diamond watermelon on record was over 300 pounds!

5) Which variety of watermelon yields high?

Your picnic-style watermelons will produce the highest yield. Varieties such as Sweet Gem, Dark Knight, and Excursion are good choices if your concern is growing an abundance of watermelons.

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