הלכה על נזיר 68:3

From the laws of the commandment is that which they, may their memory be blessed, said (Nazir 34b) that anything that comes out of the grape, whether it is the fruit or the refuse - meaning to say the zag which is the peel, and the chartsan, which is the seed that is inside it - is forbidden to the nazirite, and as it is explained in the Scripture. But behold, the leaves, the shoots, the vines and the immature berries (smadar), they are permissible; since they are not fruit and not refuse, but are considered like the tree. [This] and the rest of the many details of the commandment are elucidated in the tractate that is built on this, and that is Tractate Nazir.