Retaining walls, raised beds and other structures are used for a variety of reasons. Retaining walls are predominantly made from timber, concrete blocks or reinforced concrete and need to be strong enough to hold water as well as soil. In a lot of cases, drainage will be required to relieve the build-up of water behind the wall. Raised beds need not be as strong or as heavy as retaining walls. Both types are there to add screening or structure to help unify your garden style.
