Stones of all shapes and sizes pressing down on watermelons across vast fields is a familiar sight to locals in China. Watermelon farmers there have a long-standing habit of placing stones on their fruit to ensure the best quality as the melons approach harvest time.

For generations, watermelon has been a staple fruit for people. With its green rind, deep red juicy flesh, and refreshing sweetness, watermelon is often enjoyed as a thirst-quencher and cooling treat during hot summer days. In addition, it contains a wealth of nutrients beneficial to health.

To meet consumer demand, watermelon production has increased in many countries. However, a recently circulated photo of a Chinese farmer’s watermelon field puzzled social media users, who couldn’t understand why stones were being placed on melons just before harvest.

Why do farmers put stones on watermelons?

According to Chinese media, farmers place stones on top of watermelons to prevent birds from pecking at them. Normally, birds need to perch directly on the melons in order to feed. With stones occupying the surface, the birds lose their landing spot.

After a short time, unable to find a way to eat the fruit, the birds eventually fly off in search of better food sources elsewhere.

Some farmers also use stones to mark which watermelons are ripe and which are not yet ready for harvest. On a large field, most melons require at least one month to ripen fully, but some can mature early in just about 27 days.

Therefore, placing a stone on top of a watermelon is a practical method that makes harvesting easier and more efficient.

Another reason is to protect the fruit from harsh sunlight. Extreme heat and glare can damage the quality of the watermelon. Farmers often choose large, flat stones to cover the melons, creating shade that helps protect them from direct sun exposure.

Stones also help watermelons grow evenly. As they ripen, melons tend to develop in a straight and uniform shape. Farmers use stones to stabilize and guide this growth.

Another purpose is temperature regulation. Stones quickly absorb heat and release it efficiently, cooling the fruit at night. Scientists have shown that large fluctuations between daytime and nighttime temperatures can enhance the sweetness of watermelons. The concentration of fructose—the natural sugar that determines sweetness—intensifies as temperatures drop. This is why chilled watermelons often taste sweeter and more flavorful.