I went to my grandmother’s garden to play but I don’t understand why she threw stones at the melons..

First, the stones deter birds from eating the watermelons. When birds land on a melon with stones, they cannot hold on tightly and eat it. So the birds get scared and fly away.

Second, farmers mark the melons as ripe. Watermelons usually take up to a month to ripen after fruiting.

Third, people put ice on watermelons to avoid sunlight.

Fourth, to let watermelons grow evenly. When watermelons reach a certain size, their fruits will grow vertically. If the ice is heavy enough, the watermelons will grow more evenly.
Fifth, to improve the quality of watermelons.