How does mulch work?
Mulch works by suffocating weeds. The weeds are deprived of light and in order for them to grow, they have to break through the barrier formed by the mulch. The depth of the mulch will be determined by the weeds that you are trying to control. Vigorous weeds will need a greater depth of mulch than perhaps small annual weeds. Most weed seedlings will require covering with mulch to a depth of 8‑10 cm. Some weeds like nutgrass may break through any mulch barrier so weedicide may still be needed.
