[Leasing a Farm for Specified Years]

Answer—and Allah grants success: What appears to me—Allah knows best—is that the lease is valid:
1- By analogy with hiring a woman for breastfeeding; the scholars have held that valid, based on what has come in the Qur’an. It is known that suckling involves two things: first, tending to the infant’s care; second, nursing him with the nurse’s milk. The nurse’s milk is non-existent at the time of hiring, yet that is not a ground preventing the validity of the lease.
Likewise here: the lease’s including the (eventual) sale of non-existent fruit is not a bar to the validity of leasing the land.
2- Because the scholars state we must carry Muslims’ contracts upon validity whenever possible.
Moreover, in al-Muhadhdhab there is what indicates the validity of renting trees for a specified period, where he said: “Purchasing dates on the palm is not valid unless the buyer cuts them at once, or he rents the palm for a specified term for a specified rent.”
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2