Alms Tax: Giving the Value of Zakat
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1902
It is not obligatory to wait until wheat and barley are ready for threshing, or until grapes and dates become dry, and then give zakat; rather, once zakat becomes obligatory, it is permitted (jāʾiz) to calculate the value of zakat and give the value of it with the intention of zakat.
-Ayatullah Sistani, Practical Laws of Islam, Alms Tax (Zakat)