Privacy fences are often an essential feature of the urban backyard, and they may even play a role on some rural landscapes. Privacy fences work in both directions. Firstly, they screen out unpleasant external sights and sounds that would otherwise impinge upon the senses. Secondly, increase privacy.
Choosing shrubs for privacy screens, however, doesn't necessarily entail growing a hedge -- or sticking exclusively with shrubs, for that matter. The "loose border" is an alternative to hedges. While hedges are usually homogeneous, a loose border can be composed of different kinds of evergreen shrubs, as well as deciduous shrubs. If you are not limited for space, chances are you will find a loose border of shrubs, mixed with other plants, more to your liking than the formal austerity of hedges.
In planning for a loose border, select shrubs that will attain the desired height and width. To act as effective privacy screens, shrubs with dense growth habits have obvious advantages. Part of the attraction of the loose border alternative is low-maintenance. You are thus defeating the purpose if you plant shrubs that will outgrow the bounds intended for privacy screens, forcing you to get out there with the pruning shears and restore order.
Privacy screens taking the form of such loose borders should be layered for maximum effect. That is, put your tallest plant selections (probably tall shrubs) in the back row, shorter shrubs and tall perennials in the middle row, and your shortest plants in the front. In fact, building attractive privacy screens of plants means adhering to the same design principles one would employ in designing a perennial flower bed, including: