Square watermelons are watermelons grown into the shape of a cube. This is generally intended for space efficiency in small refrigerators. The practice of growing cube watermelons is popular in Japan. However, the cube watermelons are often very expensive and therefore are sold more as an ornamental novelty.
Square watermelons were intended to fit more compactly in fridges and be able to be cut more easily (without rolling). They were invented by graphic designer Tomoyuki Ono in 1978. She presented the watermelons in a gallery in Ginza, Tokyo. She also applied for and received a patent in the United States.
According to the BBC, the watermelons were invented during the 1980s by a farmer who lived on Shikoku in Zentsuji, Kagawa. The melons are grown in boxes and assume the shape of the container. They tend to appeal to wealthy or fashionable consumers because in 2001 they cost anywhere from two to three times a normal watermelon (at about $83).
Since the advent of the square watermelon, other watermelon shapes have been introduced, such as hearts and pyramids.