Your New Favorite Fruit: Japanese Watermelon

by Flora Baker

You might think that square watermelons are hard to grow, or that there aren’t many of them around. But you’d be wrong on both counts! In fact, cube shaped watermelons are commonly sold throughout Japan, and they can be seriously pricy – sometimes as much as US$200 per melon.  

But what makes Japanese watermelon so different from other melon varieties you find on supermarket shelves? We’ve discovered all the secrets about this fascinating fruit, so keep reading! 

What is Japanese Watermelon?

Japan is well known for its unique traditions and cultural quirks, so it’s not surprising that the strangest shaped watermelon comes from here. Japanese watermelon is unique because it’s grown in the shape of a cube. These melons are also typically regarded as ornamental rather than edible: they’re purchased for gifts and used as centerpieces in people’s homes.  

image of a slice watermelon

Where did Japanese Watermelon Come From?

Like so many inventions that make you say, “Why didn’t I think of that?”, the idea of square watermelons first arose in response to a need. In this case, it was how to store awkwardly shaped oval melons inside refrigerators, where they’d either roll around or simply take up way too much space. A graphic designer named Tomoyuki Ono decided to address this issue, and in 1978 he presented cube melons at an art gallery in Ginza, Tokyo. 

It didn’t take long for the square watermelon trend to catch on. The cubed fruit could be stacked for neatness, both at home and for transportation – plus they looked wonderfully weird and made great table centerpieces and focal points in display windows. 

Nowadays, the southern Japanese city of Zentsuji in Kagawa prefecture is home to Japan’s square watermelon industry. The city actually has a patent on square watermelons so it’s the only place where they’re allowed to be grown and farmed. Watermelon farmers are even experimenting with other shaping, which has yielded watermelon hearts and pyramids too!  

How are Japanese Watermelons Grown? 

Of course, these melons don’t naturally grow into cubes (although we’re sure some people hope this might be true!). There are no square-shaped watermelon seeds to be planted, either. Japanese cube watermelon isn’t even a specific species or variety. In fact, you could feasibly grow square watermelons at home in your own vegetable patch!

The method for creating a Japanese watermelon is all in the manipulation of the growing process. Back in 1978, Tomoyuki had used simple molding frames to shape the fruit, and that technique is still used today. 

 When the young watermelon is still developing on the vine, a transparent glass box is placed around it. The fruit then grows accordingly, filling all the space available to it, which results in a neatly uniform square-shaped watermelon. 

Farmers remove the watermelon from their boxes when they grow to a size of around 19cm in diameter, when they’re duly stacked up neatly and shipped to supermarkets. 

Black Watermelon vs Cubed Watermelon: What’s The Difference? 

You may also have heard of black watermelons, which are another seriously pricey Japanese melon. Known as densuke, these black watermelons are only found in the northern island of Hokkaido. They have shiny black skin and a crisp, crunchy texture, with a flavor that’s much sweeter and wholly different to a regular melon, be it spherical or cubic. Unlike cube watermelons, the black densuke watermelons actually do have special seeds, and they’re really hard to get your hands on, which is why densuke watermelons are the most expensive in the world at up to US$6000 each.

Why are Japanese Watermelons So Popular?

If they weren’t already hard enough to find in the first place, Japanese watermelons are also way more expensive than a regular melon, usually around US$90. So why are cube melons now used predominantly a gift rather than all the helpful reasons they were initially invented for? 

Sadly, in order to make it a cube, the watermelon has to be harvested before it’s ripe – and that means it’s not particularly edible. Nevertheless, the cube-shaped melons are still wildly popular. They’re just not for eating. 

This popularity could be due to Japan’s culture of gift giving. Square watermelons make a fantastic gift when arriving at an event or anniversary, and are also regarded as a status symbol. 

There’s also the popularity of watermelon in Japanese culture generally. As a popular snack for quenching your thirst in the summer months, you’ll see people enjoying slices of these striped green fruits all over the country from June to August. Watermelon flavoring is common too, in the form of watermelon gummy candies and fish-shaped taiyaki cakes filled with watermelon mousse.