Onions which produce no seed, and the Egyptian bean, from which one withheld water thirty days before Rosh Hashanah, are tithed according to the [year] past and are permitted in the seventh [year]; if not, they are forbidden in the seventh [year] and are tithed according to the coming year. [If they are] from a field watered by rain — that he withheld water from them for two periods; [these are] the words of R’ Meir. But the Sages say: Three.