Watch a timelapse of the way that a Square Watermelon is grown in Japan. The watermelon is grown in a glass and metal box, where it molds to the shape of the box over the course of 2 weeks.
Square watermelons, or "suika," have an interesting history in Japan. They were first cultivated in the late 1970s by a farmer named Tomoyuki Ono in the town of Zentsuji, Kagawa Prefecture. The idea was to create a watermelon that was easier to stack and store, making it more practical for shipping and display.
The cube shape of these watermelons give them an aesthetic appeal, making them a popular gift. I've seen Square Watermelons before in stores, but I've never known exactly how they're grown until now. Unfortunately, they range from $100 to $300 each, so I won't be trying one anytime soon.
See also: Watch Mezerg play the electro-melon like nobody's business