Gemara

45a (Mishnah): If Nochrim worship mountains and hills, the mountains and hills are permitted, but what is on them is forbidden - "Lo Sachmod Kesef v'Zahav Aleihem";

R. Yosi ha'Galili says, "Eloheihem Al he'Harim" - their gods on the mountains, but the mountains are not their gods.

Question: Why is an Asherah forbidden? (Also trees are attached!)

Answer: It is because man had a part in (planting) it. Anything that man had a part in becomes forbidden (if it is Ne'evad).

(Rami bar Chama): R. Yosi ha'Galili and Chachamim (the first Tana) argue about the covering of a mountain. R. Yosi ha'Galili considers it like a mountain, so it is permitted. Chachamim disagree, and forbid it.

(Rav Sheshes): All agree that the covering of a mountain is not considered like a mountain. They argue about a tree that was planted and later Ne'evad. Chachamim permit it, and R. Yosi ha'Galili forbids it.

Rav Sheshes learns from the Mishnah. It forbids anything in which man had a part. This includes a tree that was planted and later Ne'evad.

46a (A reciter of Beraisos): If Nochrim worship mountains and hills, they are permitted. If they worship vegetation, it is forbidden.

Question (Rav Sheshes): This is like R. Yosi b'Rebbi Yehudah, who forbids a tree that was planted and later Ne'evad. Why not say that it was initially planted to be Ne'evad, and the Beraisa is even like Chachamim?

Answer: Presumably, the case is similar to mountains (the Reisha). Just like mountains were not initially made to be Ne'evadim, also the vegetation.

(Bnei R. Chiya or R. Yochanan): If rocks of a mountain came loose (and they were Ne'evadim), they are permitted;

(The other of Bnei R. Chiya and R. Yochanan): They are forbidden.

The lenient opinion learns from the Tzad ha'Shavah of a blemished animal and a mountain, or from an animal and a tree that dried up.

The stringent opinion learns from "Shaketz Teshaketzenu." We never expound to permit idolatry (unless the verse explicitly permits).

48a (Shmuel): If one bows to a tree, the future growth is forbidden.

Question (R. Elazar - Mishnah): If one cut it or the branches, if the new growth is removed, the tree is permitted.

Future growth is forbidden only if he cut it or the branches!

Answer #1: Shmuel holds like R. Yosi b'Rebbi Yehudah, who forbids a tree that was planted and later worshipped.

Answer #2 (Rav Ashi): All forbid future growth (like Shmuel). The Tana'im argue about whether the previous growth is forbidden.

59a: Reish Lakish saw Yisraelim drink water that Nochrim had bowed to. R. Yochanan permitted it, for one cannot forbid public water.

Inference: if the same water were privately owned, one could forbid it. Even if it were detached (e.g. in a Keli), this is like rocks of a mountain that were uprooted. We can deduce that R. Yochanan forbids them!

Rejection: No, the case is, the Nochri took the water in his hands. This is not like rocks that were uprooted by themselves.

Rishonim

Rambam (Hilchos Avodah Zarah 8:1): Anything that man had no part in, and he did not make it, if it is Ne'evad one may benefit from it. Therefore, Nochrim who worship mountains, hills, trees that were planted for fruits, flowing springs of the Rabim and animals, they are permitted and one may eat the Peros that were worshipped where they grow, or the animal. All the more so, one may eat an animal designated for worship or to be offered to idolatry.

Rambam (2): If rocks of a mountain came loose and they were Ne'evadim in their place, they are permitted, for man had no part in them.

Ra'avad: We do not know what Bnei R. Chiya held. We are stringent about the Safek.

Ran (20a DH v'Garsinan): The Amora'im argue about whether we consider the rocks to be like the mountain, for man had no part in it, or not (like the mountain), for they are detached. The Gemara did not rule like either opinion. We are stringent, for this is a Torah law. The Ramah says so. Why is the Rambam lenient?!

Kesef Mishneh: Perhaps the Rambam's text concluded that Bnei R. Chiya permit, and we follow them against R. Yochanan.

Bach (2): The Rambam holds that even the stringent opinion agrees that a Tzad ha'Shavah teaches that it is permitted. Since there is no explicit verse to forbid, he must forbid only mid'Rabanan. We are lenient about a Safek mid'Rabanan.

Shach (1): The defenses of the Kesef Mishneh and Bach are inadequate. The Ra'avad and R. Yerucham are stringent. I say that the Rambam learned from the Yerushalmi, which says that R. Yochanan forbids, and (his Rebbi) Chizkiyah, the son of R. Chiya, permits. (We follow him against his Talmid.) We do not abandon what is clear to the Yerushalmi due to the Safek of the Bavli. Also, R. Yochanan compiled the Yerushalmi, so he himself said that he forbids. Toras Chayim says similarly.

Rambam (3): If one bowed to a tree, even though the tree itself is not forbidden, all the branches, leaves and fruits that it produces as long as it is Ne'evad are Asur b'Hana'ah (forbidden to benefit from them).

Poskim

Shulchan Aruch (YD 145:1): Anything that man had no part in, and man did not make it, even if it is Ne'evad one may benefit from it.

Gra (1): This is like the Rambam and Tur. The Shach brought a proof from the Yerushalmi. There is a proof from the Bavli (59a), which says that R. Yochanan forbids. We do not rely on the flimsy rejection.

Shulchan Aruch (ibid): Therefore, if one bowed to a mountain, it is permitted. If rocks of a mountain came loose but are still in their place, and they were Ne'evadim, they are permitted.

Taz (2): The Kesef Mishneh says that they were not totally uprooted, for man did not lift them. I say that they were totally uprooted, but not through man, for the Gemara (59a) compares this to water that separated from its source.

Shulchan Aruch (ibid): The same applies to rivers and springs of the Rabim. Trees that were not planted to be idols are not forbidden.

Beis Yosef (DH u'Mah she'Chosav d'Ilanos): Rashi (45b DH Ilan) says that the first Tana permits mountains and hills and everything like them, i.e. it is attached and its beginning was not for idolatry. An Asherah is forbidden if it was planted for idolatry. Man's involvement is significant only if it was for idolatry. Planting a seed not for the sake of idolatry is not called that man was involved in it, since he did not intend for idolatry at the time. The Rambam and Ran rule like the first Tana. The Ran was unsure if planting a shoot is different. Rav says that one who bows to a house forbids it; something that was initially detached and later attached is considered detached. The Ran says that Rav could agree that a tree is attached, for it has roots. However, Rashi holds that if he planted a shoot, it is considered detached.

Shach (3): It seems that the Shulchan Aruch permits even if he planted a Yichur, like the Ran.

Shach (4): If it was planted to be an idol, this is the Asherah of the Torah, Shas and Poskim. If a Nochri planted it, it is forbidden even if it was not worshipped. If a Yisrael planted it, it is forbidden only after it was worshipped.

Shulchan Aruch (ibid): In any case, even though the tree itself is not forbidden when he bows to it, all the branches, leaves and fruits that it produces as long as it is Ne'evad are Asur b'Hana'ah.

Beis Yosef (DH u'Mah she'Chosav umi'Kol): 'As long as it is Ne'evad' means after it was Ne'evad.

Gra (3): The Shulchan Aruch rules like Rav Ashi, that all agree to Shmuel's law.