Growing a perfectly cube-shaped watermelon transforms an ordinary gardening project into a unique agricultural feat. This distinct shape is not achieved through genetic modification but by guiding the fruit’s natural growth within a rigid container. Originating in Japan, the square watermelon was initially developed to improve stacking and refrigerator storage, but it has since become a novelty item and a luxurious gift. Cultivating this unusual fruit requires precise timing, the right equipment, and careful attention to the plant’s needs throughout the confinement period.
Selecting the Ideal Fruit and Timing the Molding
The process starts with choosing a suitable watermelon variety, with smaller, rounder cultivars like ‘Sugar Baby’ often being preferred. These compact types mature quickly and are less likely to crack the mold. Before introducing the mold, the watermelon vine must be robust and healthy, as the stress of molding requires a strong plant to nourish the developing fruit.
Timing the placement of the mold is the most critical step for success. The fruit must be small enough to be gently inserted into the container without damaging the delicate stem or skin. The ideal size is typically described as being between a golf ball and a tennis ball, or roughly 6 to 10 centimeters in diameter. Placing the mold too early risks the fruit stopping growth or rotting, while placing it too late risks the fruit being too large or bursting the mold.
Required Equipment: The Cube Mold
The integrity of the final shape depends entirely on the quality and design of the cube mold, which must be sturdy enough to withstand the significant internal pressure exerted by the growing watermelon. Molds are typically made from thick, food-safe materials like acrylic or polycarbonate.
The mold must be clear and transparent to allow sunlight to reach the fruit for photosynthesis and permit easy visual monitoring of the fruit’s progress. Commercial molds also feature ventilation and drainage holes to prevent the buildup of moisture that could lead to mold or disease. These custom molds are generally sourced from specialty online suppliers.
Step-by-Step Instructions for Shaping
Once the fruit reaches the optimal size, the mold is carefully separated into its halves and gently secured around the young watermelon. The stem connecting the fruit to the vine must be positioned to pass through the designated opening in the mold, ensuring it is not crimped or strained. The two sides of the mold are then fastened securely with bolts or latches to prevent them from separating under the pressure of the fruit’s expansion.
The mold should be placed on a level surface and supported to maintain its alignment and prevent a lopsided final product. Throughout the confinement period, the plant’s care regimen remains similar to standard watermelon cultivation, requiring consistent watering and nutrient supply to support the rapid growth. Watermelons are heavy feeders, so the vine needs adequate resources to push the fruit’s flesh against the rigid walls of the mold.
Daily monitoring of the fruit inside the transparent container is necessary to check for even growth and detect any early signs of distress, such as mold, condensation, or pinching at the corners. The mold may also need to be slightly rotated every few days to ensure all sides of the fruit receive uniform light exposure, which contributes to a more evenly colored rind. If the fruit grows too quickly and appears to be dangerously close to cracking the container, it may be necessary to remove the mold early to salvage the harvest.
Harvesting and Removing the Square Watermelon
The time from placing the fruit in the mold to harvest typically takes about two to three weeks until the shape is fully formed, though the entire growth cycle is around 80 to 100 days. Traditional methods for judging ripeness, such as thumping the rind, are unreliable when the fruit is enclosed in a thick, hard plastic or glass mold. Instead, ripeness is often gauged by the maturity of other, un-molded fruits on the same vine, or by observing the tendril nearest to the fruit, which typically turns brown when the melon is ready.
Square watermelons are frequently harvested slightly before full ripeness to ensure the rind remains firm and the perfect cube shape is maintained. Once the determination is made, the mold’s fasteners should be unlatched or unbolted with great care to avoid damaging the fruit’s skin. The square watermelon is then gently lifted out of the container and cut from the vine, leaving a short stem attached for handling. The resulting novelty fruit is often used as a decorative centerpiece due to its unique appearance and is known to store well because of its shape and firm condition.