Shrubs come in a wide variety of sizes, shapes and textures. Their growing requirements are as diverse as their looks. In other words, there are shrubs that will suit nearly every landscaping plan and environment. Knowing the characteristics that shrubs tend to have in common lets you plan for the shrubs you can incorporate into your landscaping.
Look for woody, bark-covered or semi-rigid stems. Note that "shrub" and "bush" are generally descriptive--rather than botanically accurate--words for many woody perennials that tend to grow from, usually, several or numerous stems, setting branches all over the plant, and growing anywhere from 1 to 15 feet high. Shrubs differ from trees in the cluster of stems that characterizes their growth, rather than a single main stem, or trunk. Shrubs also tend to send out branches over the full height of the plant, rather than clustering all leaves at the top or overhead. Although a 15-foot-high shrub is an imposing sight, it is easily dwarfed by the 10 to 80 feet of height achieved by trees.
Note that, although they may lose leaves in the fall, shrubs are plants that are alive year-round and return to new growth every spring. Annuals, like many summer flowers, live only a single year. The word "perennial" means "through year(s)," and shrubs, as perennials, can live for many years. Perennial flower plants, such as coneflower or black-eyed-susans, may die back in the winter and start all over with fresh new stems in the spring. A perennial shrub, such as forsythia, stops blooming and loses its leaves in the fall, but the branches remain through the winter.
Remember that some shrubs, such as arborvitae or holly, are not only perennial but also evergreen. In the case of evergreen perennials, both branches and needles remain in place during the winter. Some evergreen shrubs produce berries that remain throughout the winter--until eaten by hungry birds.
Choose shrubs for part of your landscaping when you want certain areas to look the same year after year. Once established, many shrubs can grow for 30 to 50 years or longer. Annuals can be changed every season; if you were disappointed in your red zinnias, plant other colors. Shrubs are, however, long-lived. Swapping your purple lilacs for white will be a major decision, in terms of both labor and expense.