The term perennial is frequently used by gardeners to refer to herbaceous perennial flowers. Most herbaceous perennials grow and flower for several years. Some perennials are short-lived -- surviving for only three or four years. In the fall, the tops of herbaceous perennials (leaves, stems, and flowers) die down to the ground while the root system persists through the winter. In the spring, the plant grows new leaves from its crown or roots. Plants that grow from bulbs and bulb-like structures are also herbaceous perennials but are often classified separately as flowering bulbs.

An advantage of perennials is that they do not have to be planted every year. Many perennials only flower for a few weeks each year, however, with careful planning you can have some perennials in bloom most of the season. Some consideration should be given to how a plant looks when it is not in bloom. Perennials with colorful or interesting foliage can provide interest even when they are not in bloom. Annuals can be combined with perennials to produce a continuous colorful show.

Site Selection
Consider the same aspects of site selection for perennials as you do for annuals; sunlight ( sun or shade), slope, soil type, moisture requirement, drainage, and the roles plants will play in the garden. This is especially important with perennials since they are usually left in the site for several years or indefinitely. Shaded sites pose the additional problem of tree roots competing for moisture. Even when you do an excellent job of preparing the site, tree roots tend to grow back.

Select a site that does not have a severe weed problem. This is especially true for hard-to-control weeds such as bermudagrass and nutsedge. A site that has been cultivated for several years often has fewer weeds. You may decide to use a nonselective herbicide or to cover the site with clear plastic the summer before planting to reduce weed problems (referred to as soil solarization).

Many perennials need a well-drained soil. While plants will tolerate a wet site for a short period of time, most will be killed by extended periods of "wet feet". Avoid locating the perennial border in low lying areas that are subject to standing water. Incorporate a 3- to 4-inch layer of organic matter, such as pine bark mulch or compost, before planting.

Soil pH requirements vary among perennials but most prefer a pH between 5.5 and 6.5. Lime can be applied individually to those that need a higher pH. Fertilize according to a soil test or incorporate 5 pounds of 5-10-10 per 100 square feet before planting.

Selecting Plants
Observe the bloom period for perennials in your neighborhood. Chose plants that will bloom together as well as those that will be showy when little else is in bloom. To obtain details on particular plants, consult plant societies, specialty books, nurseries, and local botanical gardens.