I am unaware of any historical references to the use of knotwork besides tales and a few old carvings that show knots used to hold back a storm. Modern witches do use them as a binding, spell wise as well as physically.
Witches use a lot of symbolic magics for spells.
Wiccan Information Network, c1989. Therefore all the knots around her clothing had to be untied,and her hair had to be unbound. The witch-mother uses a variety of spells, including knots.