All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
However, before it appears to be ripe, it is not permissible to sell it with the condition that it is to be left until it becomes ripe. However, the farmer and trader may agree to what is called a Salam contract, which is that the contract will be on a fixed quantity of grains, for example, in the liability of the farmer which he gives to the trader at an fixed time in return for a price which the farmer receives in full at the time of the contract.
If the crop of the seller is damaged, then this does not affect the contract because the contract is according to named specifications and not any specific entity.
The evidence that the Salam contract is permissible is that Ibn 'Abbaas related that the Prophet came to Al-Madeenah and the people there used to buy and sell according to the Salam contract for two or three years. So the Prophet said: “Whoever makes a Salam contract on anything, let him make the Salam contract on a fixed measure, a fixed weight, and to a fixed time.”
For information on buying goods and waiting until their price goes up, please refer to Fatwa 93779.
Allaah Knows best.