Mulching depth
If your garden is mulched but you are still having problems with weeds growing through, you probably haven’t applied the mulch correctly. Mulch needs to be at least 75-100mm (3-4″) deep to control weeds.
It is very important to mulch your garden. Mulch helps to stabilise soil temperatures in the root zone and it greatly assists with water retention in the soil. Most importantly, it suppresses weed growth.