I put down a weed blocking fabric, always had problems with these weeds with the old shed that would grow under then out of the sides of the old shed (actually through the old sheds floor too!) The shed is pretty high off the ground (its hard to see in the pictures), I put it on blocks also, so no wood has direct contact with the ground, there is a solid 5 inches between the walls of the shed and the ground. I do have a lot of patio blocks (small ones), so I was thinking of putting those up as a small barrier in between the mulch and the shed.