From when is produce obligated in tithes? Figs [are obligated] from when they begin to ripen. Grapes and avashim, from when they reach the stage of be'ushah. Sumac and mulberries, from when they redden; and all red [fruits], from when they redden. Pomegranates, from when they become soft. Dates, from when they develop sourdough cracks. Peaches, from when they develop “sinews.” Walnuts, from when they form a “storeroom.” R' Yehudah says: Walnuts and almonds [are obligated in tithes] from when they form a skin.

They stated a rule concerning tithes: Anything that is a food, and is protected, and whose growth is from the ground is obligated in tithes.  And they stated another rule: Anything which is a food at the beginning [of its growth] and a food at the end [of its growth], even though one protects it to add food, [it] is obligated [in tithes when it is] small and [when it is] large. And anything which is not a food at the beginning [of its growth], but is a food at the end [of its growth], is not obligated [in tithes] until it becomes a food.