The standard depth of mulch for garden beds is between 2-3 inches. If your much is too thick (4+ inches), then it’ll keep water from getting to the soil and your plant life will be threatened by dehydration. If your layer of mulch is too thin (1 inch or less), then it’ll be easier for weeds to grow through and the ground may get exposed in some areas where the mulch gets moved. These principles apply to every type of mulch including woodchips, and they also apply to different colors of mulch such as red, black or brown.