Making use of plants and grass on Shabbos:
It is permitted to make use of grass, plants, soft canes, weeds, vegetables and any soft produce of the ground, even when they are still attached to the ground. It is however forbidden to move any of the above items with one’s hands being that all produce attached to the ground is Muktzah. Hence if one desires to make use of the above produce, he must beware not to move it with his hands [and is rather to move it with his body].
Hard canes are forbidden to be made use of at all [from three Tefach and above from the ground]. Likewise one may not make use of hard stalks of cabbage in the area above three Tefach from the ground.
 Canes that are as soft as vegetables.
 Lit. Yerek. Vetzaruch Iyun as to what this refers.
 As the decree of the Sages was only against making use of trees and the like of hard produce of the ground, however regarding plants and the like no such Rabbinical decree is mentioned. [ibid]
 Hard canes are defined as any cane which has slightly hardened and is no longer as soft as vegetables, even if they are not as hard as a tree.
 As Admur explains in 336 5-6 that below three Tefach the Sages did not make their decree.
 Furthermore, by hard canes the Sages were more stringent than even trees themselves. [ibid] As is ruled in 409/3 that if one left his Eiruv on slightly hard canes the Eiruv is invalid.