when you put mulch on your gardens it should be applied thick enough to stop
new weeds from germanating genraly this is about 100mm thick. the wy this work is that the mulch stops sun light from getting to the ground. Another thing to remenber is that mulch draws nitrogen from the soil and air to decompoise the same nitrogen that your palts need to grow. So it is a good idea to spread alittle fertalizer before you applie your mulch to your gardens. one should also applie fertalizer in a small amount when composting grass clippings. for the same reason.