Trees and Plants
The sages enacted a number of safeguards in order to ensure that one does not come to accidentally violate the prohibition against breaking off a branch or picking off a leaf or fruit from a tree on Shabbat. Among these safeguards is the prohibition against leaning on a tree or even touching a tree if it might move by doing so. Climbing a tree is strictly forbidden on Shabbat. In fact, one who climbs a tree in complete disregard of this halacha is penalized by having to remain in the tree until the conclusion of Shabbat! If jumping down from the tree is an option then one may do so. It is permitted to sit on a tree stump.
It is forbidden to place or hang an object, such as a hat or jacket, on a tree or branch on Shabbat. One may not remove an object from a tree or branch, either. In fact, it is even forbidden to place something that might be needed on Shabbat on a tree or branch before Shabbat lest one come to remove it from the tree on Shabbat itself. One whose shofar is in a tree or on a branch may not retrieve it on Yom Tov and will therefore be forced to forfeit the Rosh Hashana shofar blowing. A gentile, however, may be asked to retrieve a shofar or any other item from a tree that is needed for a mitzva on Shabbat or Yom Tov.
One may also not benefit from, or use objects that are attached to a tree. As such, one may not hang one’s jacket on a nail that is protruding from a tree. So too, one may not lie on a hammock that is tied to a tree. One may, however, use something that is “twice removed” from a tree. For example, it is permitted to place items into (or remove items from) a bag or basket, if the bag or basket is hanging on a nail or hook that is protruding from a tree. Similarly, if a jacket is hanging on a hook or nail protruding from a tree, one is permitted to remove something from the jacket pocket. As mentioned, however, it would be forbidden to remove the jacket itself from the hook or nail.
One may not smell fruits that are attached to a tree. So too, a fruit that falls from a tree on Shabbat may not be eaten or even touched until after Shabbat is over. The sages forbade eating such fruit because they were concerned that if eating such fruit were permitted, one might forget oneself and pick additional fruit, thereby violating a Torah prohibition. Furthermore, fruit that fell from a tree on Shabbat is muktza since it was in a prohibited state when Shabbat began. Even though fruits that fell off a tree before Shabbat may be eaten on Shabbat, it is forbidden to gather such fruits into a pile. Rather, they must be gathered (or eaten) individually. One may pick fruit off a branch that was broken off or otherwise removed from a tree before Shabbat.
All the precautions and prohibitions concerning trees on Shabbat apply only to trees that are more than three tefachim (about ten inches) high. Trees and bushes below this height are generally not restricted in any way. As such, there are no Shabbat restrictions with touching, walking, or lying on grass, and the like. Nevertheless, one should not run in extremely tall grass that is likely to be pulled out or ripped in the process. It is interesting to note that the entire prohibition against riding animals on Shabbat is due to the concern that one might break a branch off a tree while riding. Nevertheless, it is forbidden to ride an animal even in an area where there are no trees or there is otherwise no reason to suspect that one might pull a branch off a tree.
Potted plants should not be moved on Shabbat. It is permissible, however, to smell potted plants. It is even permitted to touch the stems and branches of such plants if they are not expected to break by doing so. Flowers, even if still growing in the ground, may be touched and smelled, as well. Flowers that are in a vase are not muktza and may be moved on Shabbat. Nevertheless, one may not intentionally move plants or flowers to a sunnier spot in order to promote their growth or hasten the opening of their buds. Flowers should not be placed in water on Shabbat. It is permitted to remove flowers from a vase on Shabbat as long as they have not sprouted roots in the water. Water may not be added to a vase on Shabbat but one may add water to a vase on Yom Tov. One should not create floral arrangements on Shabbat.
 Eruvin 100a; Mishna Berura 336:2.
 Rema, OC 336:13.
 Beitza 36b; Rambam, Hilchot Shabbat 21:10; OC 336:1, 336:13; Mishna Berura 336:1.
 OC 336:1; Mishna Berura 336:7.
 Shemirat Shabbat K’hilchata 26 note 42.
 Aruch Hashulchan, OC 336:13.
 Mishna Berura 336:6.
 Mishna Berura 336:12; Shemirat Shabbat K’hilchata 26 note 55. See also Tehilla L’david 277:7
 OC 586:21.
 OC 336:13,59,60.
 OC 336:13; Mishna Berura 336:59.
 OC 336:12; Mishna Berura 336:63.
 OC 336:10.
 OC 322:3.
 OC 322:3; Mishna Berura 377:7.
 OC 340:10; Mishna Berura 340:37; Aruch Hashulchan, OC 340:2.
 Rema, OC 336:8.
 OC 336:2; Mishna Berura 336:21. But see Mishna Berura 336:19.
 OC 336:3; 312:6; Aruch Hashulchan, OC 312:9, 336:14,17.
 Mishna Berura 336:25. But see Aruch Hashulchan 336:21 and Shemirat Shabbat K'hilchata 26 note 69.
 Shabbat 154b; Rambam, Hilchot Shabbat 21:19; OC 305:18.
 Mishna Berura 336:2.
 OC 336:8; Mishna Berura 336:43; Shaar Hatziun 336:38; Chayei Adam 12:2; Shemirat Shabbat K’hilchata 26 note 6; Shevet Halevi 6:167; 7:184:1; Tehilla L’david 336:6. See also Shevet Halevi 4:36.
 Mishna Berura 336:48.
 Mishna Berura 336:48.
 Rivevot Ephraim 1:258.
 Rema, OC 336:11; Mishna Berura 336:53; Shemirat Shabbat K’hilchata 26:25; Har Tzvi, OC 211; Shevet Halevi 4:36. .
 Mishna Berura 336:54. But see Shaar Hatziun 336:48; Yechave Da'at 2:53.
 Shemirat Shabbat K'hilchata 26:26.
 Mishna Berura 336:54.
 OC 654:1; Aruch Hashulchan, OC 654:2; Shemirat Shabbat K’hilchata 26:26.
 Igrot Moshe, OC 4:73.