Mulching is one of the best ways to retain moisture in your landscape. If mulching every year, there is no need to go thick. A dusting to an inch is all you will need. For areas that were just recently planted new, and you have just created a flower bed, then you will need 3-4 inches of mulch to begin. If you don’t apply enough mulch, then it will promote weed growth and not help with water retention. I highly recommend mulching around stand alone trees in the landscape. By putting a mulch ring around, you will not have to weed whack along the base of the tree each week, and this will protect the tree against girdling.