Whether you want to create a safe place for your children to play or block your view of the engine rebuild next door, separating your yard from your neighbor's also adds design advantages. If you use wood or metal, enclosing your yard provides structure to the garden and an interesting visual contrast to natural elements. If you use natural elements, you gain a sense of privacy, even with a low fence or sunken boundary line.
Fences and Trellises
Standard fencing, which is a quick and easy way to separate your yard from your neighbor's, presents a blank canvas for decoration. Cover it with vines, paint a mural, hang a picture frame filled with succulents or build the fence using driftwood. Instead of a full fence, you could place two or three freestanding trellis panels, giving the suggestion of privacy while not completely blocking the view. Even low fences and see-through fences create strong boundary lines.
Your choice of shrubs and plants for hedging is huge, from small conifers to large evergreen shrubs, planted either in the ground or in large containers. Dwarf or full size brush cherry (Eugenia myrtifolia), for U.S. Department of Agriculture plant hardiness zones 9 through 11, provides a medium-height, compact privacy hedge. For a large space in USDA zones 8 through 10, try a fast-growing California wild lilac (Ceanothus).
Planting a variety of shrubs and small trees gives you the same separation effect as planting a hedge but eliminates pruning tasks and provides more height than most hedges. Possible choices for trees include mugo pines (Pinus mugo) for USDA zones 3 through 7, or pagoda dogwood (Cornus alternifolia) for USDA zones 4 through 8. For USDA zones 7 through 8, try an evergreen azalea (Rhododendron indicum) to add bright, springtime flowers under the trees.
Dry Stream Bed or Rain Garden
Rain gardens, planted in shallow depressions with plants that survive flooding, and dry stream beds, shallow, curving depressions lined with stones, don't provide privacy, but they do create natural boundaries. They also collect runoff from heavy storms, allowing excess water to seep back in the ground. Good plants for rain gardens include red twig dogwood, (Cornus sericea), for USDA zones 3 through 7, or switch grass (Panicum virgatum), for USDA zones 5 through 9.