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We are beginning Klal 12, which discuses the melacha of kotzair.
The Chayei Adam writes that one who cuts something from its source of growth, whether by hand or with a utensil, is chayav for the melacha of kotzair. This applies both to items which grow directly from the ground, such as wheat or flowers, or items which grow from a tree. Pulling an item off a tree with one’s mouth is considered a shinui, and is not assur mideoraysa. However, it is assur miderabanan.
The Chayei Adam continues, and writes that the place from which the item is being cut does not necessarily have to be the ground. If it is growing in some sort of medium, it is kotzair to remove it from that place, as we have learned recently (s346). Examples of this point include mushrooms or fungus, which can grow from detached pieces of wood or other various places. Similarly, a bucket in a well tends to grow moss on it due to the moisture, so removing the moss from the bucket would be kotzair. Another example would be moss which grows on a rock.
The Chayei Adam uses the word toleish to describe the removal of the item in the above cases. The word toleish is primarily used when an item is removed by hand, which is the standard way to remove plants in these cases.
The Nishmas Adam discusses whether there is a difference between toleish and kotzair in the sense that toleish is a shinui and kotzair (ie, using a utensil) is the normal issur deoraysa. However, the assumption of the poskim is that they are both chayav mideoraysa. Thus, although the Chayei Adam uses the word toleish, the halacha would apply equally if using a utensil.
Summary
Kotzair is defined as cutting something, either by hand or with a utensil, from its source of growth, regardless of whether that source is the ground or another medium.
Kotzair with one’s mouth is a shinui and assur miderabanan.
