Square watermelons, originally cultivated in Japan, are shaped into a cube during their growth cycle rather than being genetically modified. This practice began to make the typically round fruit easier to store and ship, though they are now most often sold as a high-end novelty or decorative item. Growing a square watermelon is a unique project for home gardeners that requires attention to detail and specific horticultural practices. This guide provides a practical, step-by-step approach for successfully shaping this unusual fruit.
Selecting the Right Watermelon Variety and Molds
The success of a square watermelon project begins with choosing the correct plant variety and shaping container. ‘Icebox’ watermelons are the most suitable choice because their mature size is manageable for standard molds. Varieties such as ‘Sugar Baby’ are ideal since they are compact, uniform in shape, and mature quickly, reducing the time the fruit spends in the restrictive environment.
The mold itself must be strong, rigid, and transparent to withstand the internal pressure of the expanding fruit while allowing photosynthesis. High-quality molds are typically constructed from thick, clear polycarbonate or acrylic material. These containers are designed in two interlocking halves to be secured around the young fruit. They feature a small opening for the vine and multiple ventilation holes to prevent moisture buildup. Ensure the mold size matches the expected mature size of the chosen variety, as a mold that is too small can lead to cracking.
Applying the Mold: Optimal Timing and Technique
The most critical factor in successful shaping is applying the mold at the precise moment of fruit development. The watermelon must be large enough to survive the process but small enough to fit easily inside the mold without being crushed. The optimal size for placement is generally between that of a golf ball and a softball, depending on the mold dimensions. Applying the mold too early may stunt growth or cause rot, while waiting too long risks the fruit cracking the mold due to rapid expansion.
Before application, carefully clean the young watermelon to remove debris or moisture that could encourage rot inside the sealed environment. Fit the two halves of the mold together over the fruit and secure them tightly, typically using bolts and wing nuts. Ensure the vine passes gently through the designated hole, remaining undamaged and free from constriction. If the mold is heavy, use a stable surface or a supportive sling from a trellis to prevent the weight from damaging the fruit stem or main vine.
Daily Care and Monitoring During the Shaping Phase
Once the mold is secured, the shaping phase requires consistent observation to manage issues arising from confining the rapidly growing fruit. Daily inspection is necessary to check for signs of stress, such as the clear walls of the mold bulging outward or heavy condensation inside the container. Excessive bulging indicates the fruit is expanding too quickly and may soon crack its rind or the mold itself.
The vine’s overall health must be maintained with regular watering and feeding to ensure the fruit has sufficient energy to expand into the cube’s corners. The vigorous growth needed to fill the mold depends on a steady supply of moisture and nutrients. To ensure the fruit develops a uniform green color on all sides, rotate the clear mold every few days to expose each face to sunlight. This rotation also helps prevent a pale or yellow patch from forming where the fruit rests on the ground.
Harvesting the Finished Square Watermelon
Determining ripeness in a square watermelon is challenging because the mold obscures many traditional indicators, and the altered shape makes the common ‘thump test’ unreliable. Growers must instead focus on the vine and skin characteristics visible through the clear container. The most dependable sign of maturity is the tendril closest to the fruit stem turning completely brown and dry.
A subtle change in the rind’s appearance, transitioning from a glossy shine to a dull, matte finish, can also be observed through the clear walls. Additionally, monitor the field spot—the area that rests on the ground—to ensure it has developed a creamy-yellow color, a reliable sign of sugar development. Once maturity is confirmed, carefully separate the mold by unscrewing the fasteners and gently lifting the two halves away. The freshly shaped watermelon should hold its unique cubic form, though it may have minor sticky residue or slight surface imperfections.