It is not permissible
for you to sell the watermelons until they are ripe and suitable for eating. The Prophet (peace be upon him) forbade selling fruits before their condition is known (free from blight). This is for fear that the crops may be destroyed and stricken with blight before its condition is known and then people's wealth would be consumed without right. It is permissible for you to rent the piece of land for a certain period with a fixed sum of money. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.