Why Do Farmers Put Stones on Top of Watermelons?

If you walk past watermelon fields in some parts of China during harvest season, you might notice something strange: many of the melons have stones placed right on top of them.

At first glance, it looks unusual — even unnecessary. Growing high-quality watermelons already requires careful work, from planting and fertilizing to weeding and watering. So why add rocks on top of the fruit just as it’s about to ripen?

According to local farmers, this simple trick actually serves several practical purposes.

1. Marking Ripeness for Harvest​

Watermelons in large fields don’t all ripen at the same time. It can take around a month for a fruit to fully mature, with the fastest ones still needing at least 27 days.

Placing a stone on a watermelon acts as a simple marker. Farmers can easily identify which fruits are close to harvest without having to inspect each one individually. It’s a low-tech but highly effective system.

2. Reducing Direct Sun Exposure​

A stone placed on top of a watermelon can also help shield it from harsh sunlight.

During the day, the stone absorbs heat and slightly reduces the intensity of direct sunlight hitting the fruit’s surface. At night, as temperatures drop, the stone cools down as well.

This creates a larger temperature difference between day and night — a condition that scientists say can help improve the fruit’s development and increase sugar content, making the watermelon sweeter and more flavorful.

3. Helping the Fruit Grow More Evenly​

As watermelons grow larger, they can sometimes develop uneven shapes.

Placing a stone of appropriate weight on top can help guide more uniform growth, encouraging the fruit to develop in a balanced way rather than elongating or becoming misshapen.

4. Preventing Rolling on Slopes​

In areas where watermelons are grown on sloped land, there’s another practical reason.

A stone helps keep the fruit in place, preventing it from rolling downhill. Without this, the melons could bump into each other, crack, or become damaged — reducing their quality and market value.

5. Keeping Birds Away​

The stones can also act as a simple deterrent for birds.

When birds try to land on a watermelon, the presence of a stone makes it harder for them to balance. As a result, they are less likely to stay and peck at the fruit, helping protect the crop.

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A Quick Note About Watermelons​

Watermelon (Citrullus lanatus) is a member of the gourd family and is believed to have originated in southern Africa. Known for its high water content and refreshing sweetness, it’s a popular summer fruit around the world.

Beyond being hydrating, watermelon also provides vitamins and micronutrients. It’s often associated with benefits like supporting hydration, aiding muscle recovery, and contributing to overall heart health.