Zakaah is due on coffee if it reaches the nisaab, because it is a kind of grain that is weighed and stored. Muslim (979) narrated from Abu Sa’eed al-Khudri (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “There is no zakaah due on less than five wasqs of dates or grains.”
In Fataawa al-Lajnah al-Daa’imah li’l-Ifta’ it says: Coffee is a kind of grain which is weighed and stored, so zakaah is due on it if it reaches five wasqs. A wasq is sixty saa’s of the Prophet’s saa’, and the time to estimate the amount is when it is ripe. What must be paid is one-tenth if it is irrigated at no cost, such as by rain, floods and water underground that is accessed by the plant’s roots; and half of one-tenth if it is irrigated at a cost such as using artificial and mechanical means. If it is irrigated for half the year in one way and for the other half in the other way, then three-quarters of one-tenth is due. The evidence that one-tenth must be paid for that which was irrigated without any cost, and one half of one-tenth for that which was irrigated at a cost, is to be found in the report narrated by al-Bukhaari from Ibn ‘Umar (may Allaah be pleased with him), that the Prophet (peace and blessings of Allaah be upon him) said: “For that which is irrigated by the sky and springs or by other natural means, (the rate is) one tenth, and for that which was irrigated by artificial means, (the rate is) half of one tenth.”
With regard to three-quarters of one-tenth being due, if one scenario exists throughout the year, then the full due should be paid accordingly. But if the scenario exists only for half of the year, then half of what is due according to that scenario should be paid. The amount collected should be spent as all other zakaah of grain and crops is spent.
Fataawa al-Lajnah al-Daa’imah (9/234).
And Allaah knows best.