There are lots of different varieties of mulch ranging from the kind you see on the side of the road to the gorilla hair you see at houses for sale. Roots 'n Shoots prefers fir microbark even for banks. Mulch is laid down over a garden at approximately two inches thick at least. Mulch retains moisture and protects the plants. It also hides the irrigation lines. Plus it just looks good. We always recommend mulch.