Black Diamond watermelon is an open-pollinated heirloom variety of Citrullus lanatus prized for dark green rinds, dense red flesh, and melons that often weigh 30 to 50 pounds at maturity. Its nutritional profile tracks closely with other red watermelons, delivering about 90 percent water per bite alongside lycopene, beta-carotene, vitamin A, vitamin C, citrulline, and potassium, while larger-than-average portions raise the stakes on natural sugar and glycemic impact.
You’ll find the variety’s full nutritional breakdown, health benefits, side effects, and side-by-side comparison with grocery melons below, along with selection cues and storage rules so the fruit you cut lives up to its reputation.
An Heirloom Giant With a Dark, Striking Rind
Black Diamond belongs to Citrullus lanatus, the same species as every sweet watermelon sold in the United States. It was popularized in the early 1900s across the American South and remains a fixture in Mississippi, Arkansas, and Georgia gardens, where long hot summers let the fruit reach full size on the vine. The variety earned its name from the rind, which ripens to a deep, almost black green that looks bruised next to the bright striped melons in a grocery bin.
Physical Traits and Season
Expect round to oblong fruits weighing 30 to 50 pounds at maturity, with occasional specimens pushing past 70 pounds in prime growing conditions. The rind runs thick and tough, designed by nature to protect a fruit this heavy from sun scorch and rough handling. The interior is what hooks people: a bright, dense red flesh with large brown-black seeds scattered through it. Because Black Diamond is a seeded heirloom, home growers save seed year to year to keep the line going.
Black Diamond runs from late spring through early fall, peaking in July and August. That window is shorter than grocery-store melons, which often come from Mexico or Central America year-round, so seasonality shapes when you’ll see one at a farm stand or farmers market.
Flavor and Texture
Growers describe the flavor as intensely sweet with a clean, almost candy-like finish, less watery than grocery melons and with a crisper bite. The flesh holds its texture well in salads and aguas frescas, which matters when a single fruit needs to feed a crowd. Compared to common red varieties, Black Diamond tends to land higher in sugar per bite, which is the central trade-off when you weigh its benefits against its side effects.
Nutritional Profile of Black Diamond Watermelon
Weighing in at 90 to 92 percent water by mass, the dense red flesh of a Black Diamond keeps every slice remarkably low in calories per bite. That high water content is the single biggest nutritional fact about the fruit, and it shapes everything from calorie count to how refreshing a slice feels on a 95-degree afternoon. Per 100 grams of raw flesh, you get a small calorie number, mostly from natural sugars, and very little fat or protein.
Calories, Water, and Carbohydrates
A 100-gram serving of raw watermelon lands at around 30 calories, with about 7 to 8 grams of carbohydrate, most of it from naturally occurring sugars like glucose, fructose, and sucrose. A typical wedge weighing 280 grams (roughly one-sixteenth of a small melon) delivers about 85 calories. Because Black Diamond melons run larger than grocery fruit, a single thick slice can easily double or triple that standard serving.
| Nutrient | Per 100 g raw flesh | Per typical 280 g wedge |
|---|---|---|
| Calories | ~30 kcal | ~85 kcal |
| Water | ~91 g | ~255 g |
| Carbohydrate | 7.6 g | ~21 g |
| Sugar (total) | 6.2 g | ~17 g |
| Vitamin A (RAE) | 28 mcg | ~78 mcg |
| Vitamin C | 8.1 mg | ~23 mg |
| Potassium | 112 mg | ~314 mg |
| Lycopene | ~2,300 mcg | ~6,400 mcg |
Those numbers come from the standard USDA FoodData Central entry for raw watermelon and apply across varieties, with Black Diamond’s deeper-red flesh generally landing at the higher end of the lycopene range.
Vitamins, Beta-Carotene, and Lycopene
Pigments called beta-carotene and lycopene give the interior its deep crimson hue, with your body converting the former into vitamin A. Black Diamond’s deep, almost crimson interior tends to be richer in both pigments than paler commercial varieties. Per 100 grams, you get roughly 28 micrograms of vitamin A (RAE) and around 8 milligrams of vitamin C, modest numbers individually but meaningful when you eat several cups in one sitting on a hot day. Lycopene is the headline: a serving of deep red flesh can deliver around 2,300 micrograms of lycopene, comparable to a small serving of raw tomato.
Citrulline and Potassium
Watermelon is one of the richest food sources of citrulline, a non-essential amino acid the body converts to arginine, which then feeds the nitric oxide pathway involved in blood vessel dilation. The flesh contains more citrulline than the rind, and Black Diamond’s dense flesh concentrates it further. Potassium comes in at about 112 milligrams per 100 grams, a small but useful contribution to the electrolyte balance you need on sweaty summer days.
That electrolyte edge matters most when the rest of the nutrition picture lines up behind it.
Health Benefits Backed by the Flesh
Hydration is the most immediate payoff. A 280-gram wedge puts roughly 255 grams of water into your system, more than an eight-ounce glass of plain water, in a form that also delivers a small bump of electrolytes and natural sugars. For athletes, outdoor workers, and anyone in a heat wave, that combination matters, because plain water plus a slice of watermelon replaces fluid and a touch of sodium-replenishing potassium more pleasantly than most sports drinks.
Antioxidant and Heart Associations
Lycopene in the diet has been linked in observational studies to lower markers of oxidative stress and better endothelial function, the inner lining of blood vessels. A 2022 review of lycopene intake and cardiovascular markers noted modest associations between higher lycopene consumption and lower blood pressure and LDL cholesterol in some populations, a pattern large reviews in the field have echoed. Watermelon stands out because citrulline and lycopene appear together, and the combination may support vascular health in ways that either compound alone does not. None of this is a treatment, and results vary by individual.
Pair a slice of watermelon with a protein source after a hard workout and the citrulline-arginine pathway gets a practical boost alongside the hydration.
Recovery, Satiety, and Weight-Conscious Snacking
Citrulline’s role in nitric oxide production has drawn attention from endurance athletes, who report less muscle soreness after intense sessions when they consume watermelon or watermelon juice. The mechanism is plausible: better blood flow means faster waste-product clearance from working muscles. For weight-conscious eaters, the low calorie density (about 0.3 calories per gram) makes the fruit an unusually filling snack. A full cup of cubed flesh fills a bowl for around 45 calories, hard to beat for volume per calorie.
Side Effects and Who Should Eat With Caution
Even a clean, hydrating fruit has a downside when portions climb. Watermelon’s main risks are sugar load, fiber volume, and rare but real allergic reactions. Because Black Diamond fruits are larger and sweeter than grocery melons, the side effects show up faster when you keep cutting into the next slice.
Digestive Upset and Sugar Load
The same natural sugars and fiber that make watermelon sweet can also cause bloating, gas, and loose stools when you eat large amounts in one sitting. More than 500 grams (about 18 ounces) of flesh in a short window is enough to trigger symptoms in some people, especially if your gut is sensitive to FODMAPs, a group of fermentable carbohydrates. Spread intake across the day and pair watermelon with protein or fat to slow gastric emptying and reduce the spike-and-crash blood sugar effect.
Allergies and Oral Allergy Syndrome
Raw fruit proteins sometimes confuse the immune system into reacting to pollen allergens, a cross-reaction doctors label oral allergy syndrome (OAS). People allergic to ragweed, grass, or birch pollen can develop itching or tingling in the mouth and throat after eating raw watermelon. The reaction is usually mild and short-lived, but it can escalate in sensitive individuals. Cooking the fruit breaks down the triggering proteins, so a grilled or pureed version may sit better if you react to raw flesh.
Blood Sugar and Pregnancy Notes
Watermelon’s glycemic index sits around 72, high on the scale, meaning the carbohydrates convert to blood glucose relatively fast. Glycemic load per serving is low because the portion itself is small, but Black Diamond’s sweeter flesh and bigger serving sizes can push the load higher than expected. People with diabetes or insulin resistance should treat watermelon like any other high-sugar carbohydrate source: track portions, pair with protein or fat, and test blood glucose to find a personal threshold.
For pregnancy, watermelon is generally considered safe and can help with hydration and mild constipation. Watch the sugar load if you have gestational diabetes, and ask your obstetrician about portion size. Large amounts of any high-sugar fruit can also aggravate heartburn in the third trimester.
Those caveats grow sharper once you stack Black Diamond against the everyday varieties most shoppers actually find.
Black Diamond Compared to Regular Watermelon
Side by side, Black Diamond and the seedless Crimson Sweet or striped grocery melon differ more in experience than in nutrition, but the differences matter when you’re choosing what to buy or grow.
| Feature | Black Diamond | Typical Red Grocery Melon |
|---|---|---|
| Rind color | Very dark, nearly black green | Light green with dark stripes |
| Average weight | 30 to 50 lb | 15 to 25 lb |
| Seed pattern | Large brown-black seeds, seeded | Often seedless or small white seeds |
| Flesh color | Deep, intense red | Pink to red, sometimes pale |
| Lycopene level | Higher end of range | Mid to lower end of range |
| Texture | Crisp, dense, less watery | Crisp but more watery |
| Season | Late spring to early fall | Year-round (imports extend window) |
The Allsweet and Cannonball heirlooms overlap with Black Diamond in size and sweetness, and growers often plant them as cross-pollination partners. If you want the dark rind specifically, Black Diamond is the gold standard. If you want mild flavor and easier portioning, a seedless grocery melon wins on convenience.
Practical Differences for Your Kitchen
Because Black Diamond fruits run large, plan for a crowd. A single 40-pound melon feeds 25 to 30 people as a side. Once cut, the flesh browns faster than some varieties, so wrap it tight and refrigerate within two hours. Pricing tends to be lower per pound at farm stands where the melons are local and abundant, and higher at grocery stores that ship them in. Availability is the real limit: outside farmers markets and roadside stands in the South, you’ll hunt for one.
Finding one is only half the work, since a forty-pound melon can turn fast once you bring it home.
Selecting, Storing, and Preparing a Ripe Melon
Ripe Black Diamond is a heavier fruit than you expect for its size, with a dull, waxy rind that has lost the shine of an under-ripe specimen. Thump-testing works on most melons, including this one: a ripe Black Diamond sounds deep and hollow rather than flat or metallic. Look for a creamy yellow or orange field spot on the underside, the place where the melon rested on the soil, because a green or white field spot means it came off the vine too early.
Ripeness Cues and Harvest Timing
At the farm stand or your own patch, the tendril closest to the stem dries to brown when the fruit is mature. Combined with a heavy weight and a rich field spot, that tendril signal is the most reliable indicator for a dark-rind variety that hides its color changes. Rapping on the rind should produce a low, resonant sound, not a dull thud or a tight ping.
Storage Rules for Cut and Whole Fruit
A whole, uncut Black Diamond keeps at room temperature for 7 to 10 days, away from direct sun. Once cut, refrigerate the flesh in airtight containers and use it within 3 to 5 days. Cubes freeze well for smoothies if you spread them on a sheet pan first, then transfer to a bag. Whole melons can chill in the fridge for 24 hours before serving, which improves the eating experience on a hot day.
Cutting, Cubing, and Saving Seed
- Rinse the rind: Scrub the whole melon under running water with a clean brush before the knife ever touches it, because field soil and any residue on the skin can transfer into the flesh in a single cut.
- Trim the ends: Slice off the top and bottom so the melon sits flat and stable on the cutting board.
- Stand and peel: Set the melon upright and shave the rind off in downward strokes, following the curve of the flesh.
- Slice into rounds: Cut the exposed flesh into thick rounds, then strips, then even cubes for salads, platters, or the fridge.
- Save seed for replanting: Pull a few large brown-black seeds from a fully ripe specimen, rinse them, and dry on a paper towel for next season’s row.
Pesticide and Washing Guidance
Thick-rind heirloom melons like Black Diamond have less surface pesticide contact than thin-skinned fruit, but residue can still sit on the rind. Buy organic when you can, and always wash the rind with cool water and a stiff brush before cutting. A one-part vinegar to three-part water rinse works for the rind, but skip the soak because it can affect flavor. Pat the rind dry before slicing to keep the knife from slipping on a 40-pound ball.
Bottom Line
Black Diamond watermelon delivers the classic watermelon benefits: deep hydration, lycopene, citrulline, and a low-calorie way to fill up on a hot day, all wrapped in an heirloom fruit with a nearly black rind and dense red flesh. The trade-off is sugar load and portion size, which can surprise even experienced watermelon eaters. Eat it mindfully, pair it with protein, and watch your total fructose intake if you track blood sugar.
FAQ
What are the health benefits of Black Diamond watermelon?
Black Diamond supports hydration through roughly 90 percent water content, delivers lycopene and beta-carotene from its deep red flesh, and provides citrulline, an amino acid linked to circulation and post-exercise recovery. A 280-gram wedge adds vitamin A, vitamin C, and potassium for about 85 calories, making it a smart low-calorie snack on hot days.
Does Black Diamond watermelon have any side effects?
Large portions can cause bloating, gas, or loose stools because the natural sugars and fiber ferment quickly in the gut. The glycemic index is high, so blood sugar can spike if you eat a lot at once, and people with oral allergy syndrome may get itching or tingling in the mouth from raw flesh.
How many calories are in Black Diamond watermelon?
A 100-gram serving of raw flesh runs about 30 calories, and a typical 280-gram wedge (roughly one-sixteenth of a small melon) comes in near 85 calories. A full cup of cubed flesh is around 45 calories, which is one reason the fruit fits easily into calorie-controlled eating plans.
Is Black Diamond watermelon safe to eat during pregnancy?
Yes, in normal portions. The water and fiber can help with hydration and mild constipation, both common during pregnancy. If you have gestational diabetes or severe heartburn, watch the sugar load and ask your obstetrician about portion size, because a single thick slice contains a meaningful amount of natural sugar.
What nutrients are found in Black Diamond watermelon?
The flesh provides vitamin A as beta-carotene, vitamin C, potassium, lycopene, and citrulline, all within a base of about 91 percent water and 7 to 8 percent carbohydrate. Trace amounts of magnesium and B vitamins round out the profile, with the deep red interior signaling the highest lycopene concentration.
How does Black Diamond watermelon compare to regular watermelon nutritionally?
Nutritionally, Black Diamond tracks closely with other red varieties: same water percentage, similar calorie count, and comparable vitamin levels per 100 grams. Where it stands out is lycopene density, because the deeper red flesh concentrates the pigment, and in portion size, since the melons themselves can run twice as heavy as a typical grocery fruit.
