To keep it that way, the best method to stop the weed from growing through mulch is by putting a layer of weed barrier underneath. So, yes, as you can see, there’s a need to place a weed barrier even if you already have mulch. Similarly, you can pull perennial and annual weeds as soon as you can see them. Remember, pull the weeds out by their roots before they reach the seed. You can use a trowel to easily remove the roots of the weeds.
166