CONCERN LEST ONE DETACH GRASS OR VEGETATION ON SHABBOS [Shabbos: Tolesh: grass]
(Shmuel): A voluntary Korban of wine is sprinkled on the fire (on the Mizbe'ach).
Question: The wine will (partially) extinguish the fire (where it lands). This is forbidden ("Esh Tamid Tukad Al ha'Mizbe'ach Lo Sichbeh")!
Answer: Extinguishing is permitted for a Mitzvah (e.g. a Nedavah of wine).
Question (Beraisa): Nesachim of wine are poured into the Sefalim.
We cannot say that they are thrown onto the fire, for it says "Lo Sichbeh"!
Answer: Shmuel holds like R. Shimon, who permits Davar she'Eino Miskaven (something one does not intend for).
Eruvin 34b (Mishnah): An Eruv on top of a reed that was initially detached and later inserted into the ground is valid.
(Ravina): This is like Rebbi. He decrees to forbid an attached reed, lest one cut off the top when taking his Eruv.
Rav Nachman (to his Talmidim): Go bend reeds for us to sit on tomorrow (Shabbos).
Question (Rami bar Chama): The Mishnah does not permit a reed that was initially attached! (It is like a tree, and it is forbidden on Shabbos.)
Answer (Rav Nachman): That refers to reeds that became hard like a tree.
100a (Beraisa): If roots of a tree are three Tefachim above the ground, one may not sit on them, for one may not climb a tree, hang on it or lean on it.
100b (Beraisa #1): The same (Isur) applies to a moist or dry (dead) tree.
Contradiction (Beraisa #2): A moist tree is forbidden, but a dry tree is permitted.
Resolution: We permit in summer (people know that it is dead because it has no leaves), but forbid in winter (due to suspicion).
Question: If we permit a dry tree, fruits will fall off, and people will come to detach from living trees!
Answer: The case is, it has no fruits.
Question: Twigs will break off, and people will come to detach from living trees!
Answer: The case is, it is a barren stump without branches.
Question: Rav visited Apastiya and forbade such a tree!
Answer: Rav saw a need to be stringent. (The people there were unlearned.)
(Rami bar Aba): One may not walk on grass on Shabbos - "v'Atz (one who tramples) b'Raglayim Chotei."
(Beraisa #1): One may walk on grass on Shabbos.
Contradiction (Beraisa #2): One may not walk on grass on Shabbos.
Resolution #1: One may walk on dry grass on Shabbos, but not on wet grass.
Resolution #2: Both Beraisos discuss wet grass. One discusses winter, and the other discusses summer.
Resolution #3: Both Beraisos discuss summer (some texts - winter). It is permitted if he wears shoes, but forbidden in bare feet.
Resolution #4: Both Beraisos discuss one who wears shoes. It is forbidden in shoes with spikes, and permitted in shoes without spikes.
Resolution #5: Both Beraisos discuss shoes with spikes. It is permitted on short grass, and forbidden on long grass.
Shabbos 82a (Rav Chisda or Rav Hamnuna): (On Shabbos) if one has a pebble and grass, he cleans himself (in the privy) with the pebble, but not with the grass.
(The other of Rav Chisda and Rav Hamnuna): He uses the grass, but not the pebble.
Question (against the latter opinion - Beraisa): Cleaning with something that can burn causes the anal teeth to fall out.
Answer: The latter opinion discusses wet grass, it does not burn.
Rambam (Hilchos Shabbos 1:5): If something is permitted on Shabbos, but while doing it, it is possible that a Melachah will or will not be done, if he does not intend for the Melachah, it is permitted. One may walk on grass on Shabbos as long as he does not intend to uproot it. Therefore, if it became uprooted, he need not be concerned.
Rambam (21:6): One may not go up a tree, whether it is moist or dry. One may not hang on it or be supported by it. One may not use anything attached. This is a decree lest he detach.
Magid Mishneh: The Gemara answered that a dry tree is permitted in winter. Rav forbade at all times; this was a fence. The Meforshim say that we rely on this to forbid all trees. The Rambam agrees.
Rambam (26:5): If one had a pebble and grass, if it is soft grass he cleans himself with it. If not, he uses the pebble.
Magid Mishneh: He rules like the opinion that we use the grass. Rashi explains that wet grass does not burn. It seems that the Rambam agrees. The Rif and Sefer ha'Itim say oppositely. They permit only dry grass, but moist grass causes the anal teeth to fall out.
Beis Yosef (OC 312 DH Tzeror): Our text of the Rif (distinguishes between moist and dry leaves, but does not specify we use) does not connote oppositely.
Rosh (Eruvin 10:12): (Initially) we forbid in winter, for then grass is hard and it is prone to break. We permit in summer, when the grass is soft and bends. We conclude like R. Shimon, and permit walking on grass in every case. We should decree about a dry tree, for it is more prone to break off. We cannot prove from here that a dry tree is permitted. It seems that the Rif does not distinguish between trees and grass, and this is why he omitted the law of dry trees.
Rosh (Shabbos 8:2): One cleans himself with moist grass, but not with dry grass, lest it cause the anal teeth to fall out.
Hagahos Ashri: The first opinion says not to use grass, for even if it is moist and does not burn, it causes the anal teeth to fall out.
R. Yehonason (on Rif Eruvin 33b DH Asur): (Initially, we say that) one may not walk on wet grass due to detaching. Dry grass is considered as if it were already detached. We are stringent in summer when grass is close to drying out, and it is prone to break.
Rashi (Shabbos 82a DH v'Eino): The first opinion says not to use grass, for it is moist and it cuts the flesh. My Rebbeyim say that the concern is uprooting it. I do not understand. Surely, no one permits attached grass! It seems that they hold that it is attached, and he uses it and leaves it attached.
Shulchan Aruch (OC 336:3): One may walk on grass on Shabbos, whether it is wet or dry, since he does not intend to uproot it.
Beis Yosef (DH Mutar): The Gemara concluded that it is permitted in every case, for we hold like R. Shimon, who permits Davar she'Eino Miskaven.
Bach (5): The conclusion permits even wet grass, which is not considered detached, even in summer when it is prone to break, even in bare feet. Even though grass sticks between his toes and is uprooted, it is Davar she'Eino Miskaven. It is not a Pesik Reishei. If there is no textual error in the Rosh (who is more lenient in summer), we must say that everyone explains based on the grass in his locale.
Taz (6): One may walk on it, but he may not use it. The Rambam forbids using even Yerek (other vegetation).
Kaf ha'Chayim (25, citing Eliyahu Rabah): The Taz holds that we permit only walking, for the hands are far (from the grass, so we are not concerned lest he detach), but one may not use it. This is wrong. (Rather, one may use it.) The Gemara taught the Heter to walk on it, for this is a bigger Chidush. It is more prone to get uprooted through walking than through using it, especially if he walks barefoot.
Mishnah Berurah (24): The Shulchan Aruch connotes that we permit walking even barefoot on long grass, and the grass clings between his toes, for it is not a Pesik Reishei that it be detached. Therefore, even if it is detached, it is not an Isur, for he did not intend. However, if he finds grass between his toes or on his shoes, he may not remove it with his hand. It is Muktzah, for at the start of Shabbos it was attached.
Mishnah Berurah (25): One must be careful not to run on long grass, for it is a Pesik Reishei that it will be detached. Perhaps one must be careful even about walking quickly on it.
Bi'ur Halachah (DH Mutar): Semag says that we do not climb trees on Shabbos; this is a decree lest one detach; also in Eruvin, we say that one may not walk on grass in a place where he is sure to detach. This is astounding. The Gemara concluded that every case mentioned is permitted, since we hold like R. Shimon! Also the Maharshal's explanation of Semag is astounding. He says that all of these (cases that the Gemara initially forbade) are a Pesik Reishei. It is permitted because it is not Meleches Machsheves (the Torah forbids only intended Melachah). This is unlike many Rishonim, who say that it is not a Pesik Reishei. Even if this were all true, Semag is difficult. The Gemara concluded that every case is permitted! Actually, Semag is from Sefer Yere'im. Rami bar Aba forbade walking on grass due to "v'Atz b'Raglayim Chotei." Semag and the Yere'im did not want to explain that is only in the Hava Amina. Rather, it is even like the conclusion, that we hold like R. Shimon. He discusses a case that is a Pesik Reishei, e.g. he goes quickly and runs on long grass. 'Atz' refers to rushing. The Yere'im similarly explains (in another Sugya) that Avin Tzipora'ah is not like R. Yehudah, rather, like R. Shimon, in a case that is a Pesik Reishei.
Shulchan Aruch (312:6): One may clean himself with moist grass, even if it is attached, as long as he does not move it. This is not a problem of using something attached, for Chachamim forbade only trees, but not Yerek.
Beis Yosef (DH Tzeror): Rashi connotes that even if the grass is attached, it is permitted; he may not move it. This is like it says in Eruvin 34b, that Chachamim forbade only trees, but not Yerek. Also R. Yerucham says so.
Gra: This is like Rashi's Rebbeyim.
Magen Avraham (6): One may not move it because it is Muktzah.
Rebuttal (Eliyahu Rabah): The Isur is not due to Muktzah. Rather, we are concerned lest he detach.
Eshel Avraham: Even though it is food for animals, since it is attached, it is Muktzah. One may clean himself with his body; he may not move it with his hand. One may move Muktzah with his body, even for the sake of the Muktzah. Eliyahu Rabah is difficult. The Shulchan Aruch need not teaches that one may not detach!
Machatzis ha'Shekel: Tosfos Shabbos and Eliyahu Rabah hold that Muktzah applies to Peros that were detached or fell on Shabbos. Since he did not detach them before Shabbos, he showed that he did not intend for them. One may use them when attached, unless the Isur of using something attached applies. It does not apply to grass, therefore, the only concern is lest he detach.
Mishnah Berurah (19): One may not move it from where it is attached, lest he detach it.
Kaf ha'Chayim (35): Perhaps it is permitted even with a tree; due to Kavod ha'Briyos (it is disgraceful if he cannot clean himself), Chachamim did not decree. They did not decree about attached leaves, for even if he detaches, it is Melachah she'Einah Tzerichah l'Gufah (it does not give benefit to him, or is not done for the same purpose as in the Mishkan). Also, he does not intend, and it is not a Pesik Reishei. Levush and Eliyahu Rabah say so. R. Zalman permits a tree only if he does not have rocks or pebbles.