There are four reasons why the watermelon in my world game can't grow:
First of all, players are planting watermelons, and there are no spare squares around watermelons.
The second is that when planting watermelon, the four squares around watermelon are not mud squares or grass squares.
The third is that when planting watermelon, there are other squares around and above the watermelon.
The fourth is that the server of the game prohibits the growth of crops.