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Yes, black diamond watermelons are sweet.
In fact, they’re known for being one of the sweetest and most flavorful varieties you can grow or buy.
If you’ve been asking yourself, “are black diamond watermelon sweet enough to bother growing,” the short answer is a resounding yes.
Their deep red flesh packs a sugary punch with a classic watermelon taste that’s hard to beat.
In this post, we’ll dig into why black diamond watermelons are sweet, what makes their flavor stand out, and how to pick or grow the sweetest ones possible.
Let’s get into it.
Why Black Diamond Watermelons Are Sweet
Black diamond watermelons are sweet because of their genetics, growing conditions, and the way they convert starches into sugars as they ripen.
Here’s what’s going on under that dark green rind:
1. Naturally High Sugar Content
Black diamond watermelons are a classic heirloom variety bred for flavor, not just size.
On the Brix scale, which measures sugar content in fruit, black diamond watermelons often hit 10 to 12 percent, which is impressive for a melon.
That translates to flesh that tastes consistently sweet rather than watery or bland.
The sweetness is most concentrated near the center, but a well-ripened black diamond gives you sweet, juicy bites all the way to the rind.
2. They Ripen Slowly and Fully
Black diamond watermelons take their sweet time maturing, usually 85 to 95 days from planting.
That long growing season gives the fruit plenty of time to develop complex sugars.
Unlike some fast-maturing varieties that stay mild, black diamond watermelons build up sweetness gradually as they sit on the vine.
So when you finally harvest one, the sugar has had time to fully develop.
3. Sun Exposure Boosts Flavor
Sweetness in black diamond watermelons depends heavily on sunlight.
The vines need full sun, at least eight hours a day, to produce the sugars that make the fruit taste so good.
More sun means more photosynthesis, which means more sugar stored in the flesh.
That’s why a black diamond watermelon grown in a sunny, warm climate tastes noticeably sweeter than one grown in shade or cool weather.
4. Deep Red Flesh Signals Ripe Sweetness
When a black diamond watermelon is fully ripe, its flesh turns a deep, rich red.
That color isn’t just for looks.
It’s a sign that the lycopene and sugars have fully developed.
A pale pink or whitish interior usually means the melon was picked too early, and it won’t be nearly as sweet.
So if you’re wondering are black diamond watermelon sweet, just look at the flesh color before you buy or slice.
How to Pick a Sweet Black Diamond Watermelon
Knowing that black diamond watermelons are sweet is one thing.
Actually picking a sweet one is another.
Here’s how to stack the odds in your favor:
1. Look for the Field Spot
Flip the watermelon over and find the field spot, the patch where it rested on the ground.
On a ripe black diamond watermelon, that spot should be creamy yellow or orange, not white or green.
A yellow field spot means the melon sat on the vine long enough to ripen and sweeten.
2. Check the Weight
A sweet black diamond watermelon feels heavy for its size.
That weight comes from water and sugar content.
If it feels light, it probably wasn’t watered well or was picked too early, and the sweetness will be disappointing.
3. Give It a Thump
Knock on the side of the melon with your knuckles.
A sweet, ripe black diamond watermelon gives a deep, hollow sound.
A dull thud usually means it’s underripe or overripe, and either way, the flavor won’t be at its peak.
4. Look for a Dry Tail
The tail is the small stem end of the watermelon.
When it’s green, the melon was picked too soon.
When it’s brown and dried out, the black diamond watermelon ripened naturally on the vine and should be sweet.
Are Black Diamond Watermelons Sweeter Than Other Varieties?
Black diamond watermelons are sweeter than many common varieties, though not always the absolute sweetest.
Compared to seedless watermelons or early-harvest types, black diamond watermelons often have a richer, more old-fashioned watermelon flavor.
They beat most store-bought melons because those are picked early for shipping.
A vine-ripened black diamond watermelon will almost always taste sweeter than a grocery store melon that was harvested before its time.
That said, varieties like Sugar Baby and Crimson Sweet can rival them in sugar content.
But black diamond watermelons hold their own, especially when grown in warm, sunny conditions.
1. Heirloom Flavor Matters
Black diamond watermelons are an heirloom variety, which means they weren’t bred for shelf life or uniform shape.
They were bred for taste.
That’s a big reason why black diamond watermelons are sweet and why so many gardeners keep coming back to them.
2. Growing Conditions Make a Difference
Even the sweetest variety can turn out bland if it’s grown in poor soil or cool weather.
Black diamond watermelons need warm soil, plenty of water, and a long, hot summer to reach their full sweetness.
Give them those conditions, and they’ll reward you with some of the sweetest flesh you’ve ever tasted.
3. Ripeness Is Everything
A black diamond watermelon picked a week too early will taste mild and watery.
Picked at peak ripeness, it’s sugary and refreshing.
That’s why so much of the sweetness comes down to when you harvest or buy it.
If you’re growing your own, wait for the tendril nearest the fruit to dry out and turn brown before you pick.
So, Are Black Diamond Watermelon Sweet?
Yes, black diamond watermelons are sweet and they’re one of the tastiest heirloom varieties you can grow or buy.
Their natural sugar content, long ripening period, and deep red flesh all add up to a melon that delivers real sweetness in every bite.
Pick one with a yellow field spot, a hollow thump, and a dry tail, and you’ll taste exactly why black diamond watermelons have stayed popular for generations.
Whether you grow them yourself or find one at a farmers market, a ripe black diamond watermelon is sweet enough to make you forget every bland, watery melon you’ve ever had.