A perennial is any plant that lives for three or more years when it’s grown in conditions to its liking. This is really just about one type of perennial plant — the herbaceous flowering perennial. Technically, the term “perennial” includes such giants as the majestic, centuries-old redwood and the oak tree in the city park. Unlike trees and shrubs (which have woody stems forming their twigs, branches, and trunks) herbaceous perennials have soft, fleshy stems.

Perennials that hail from cold climates usually indulge in a winter nap, called a period of dormancy. (A few herbaceous perennials go dormant in summer, instead, playing a convincing game of opossum for their uninitiated gardeners.) During the period of dormancy, the perennial dies back to the ground — that is, allows its stems and foliage to die. The above-ground parts of a dormant plant are truly dead, but the roots are alive and well. In fact, the roots may be actively growing even when the top is resting. In more moderate climates, most herbaceous perennials are evergreen (meaning that their above-ground parts are alive and kicking all year long) because they don’t need a coping mechanism, such as dormancy, to escape extreme temperatures.

Boning Up On Perennial Anatomy

Growing perennials is much easier if you have a basic understanding of how the flowers are put together. In spite of their significant variations, all the plants in this large group do share a few characteristics, as shown in the image below.

The following list examines each of a perennial’s basic parts:

• Roots: Roots pull water and nutrients from the soil and carry these essentials to the stems. The roots even store extra water and nutrients in case times get tough. The two main types of roots are fibrous roots and taproots. Fibrous-rooted perennials have a network of branching roots. Taprooted perennials have a fleshy central root (like a carrot), with smaller secondary roots growing off the main root. Taproots can reach quite deeply into the ground, but fibrous roots generally occur primarily in the top 12 inches (30 cm) of soil.
• Stems: Stems transport water and nutrients from the roots to the leaves and flowers, and vice versa. Stems can be squared or rounded, upright or low and spreading, and single or branched. Stem tissue is sometimes specialized to create thickened underground repositories, where the plant can stash extra food and water. Perennials may also spread by modified stems called stolons (or runners) that travel just beneath the surface of the ground. The stolons often send up new shoots along their length, either close by or quite some distance from the original clump, varying by the type of perennial.
• Leaves: Although stems can manufacture food for the plant, this function is primarily the role of the leaves. Leaves also help the plant regulate its moisture content and internal temperature by allowing water to evaporate from their surfaces or by wilting, when necessary, to reduce their exposure to sun and air. Leaves come in a huge variety of shapes, sizes, and textures and can occur singly or as one of several leaves attached in a group on a single stalk. A cluster of leaves at the base of the plant is called a basal rosette. Stems and flower stalks rise from this clump of leaves and often die back to the basal rosette at the end of the growing season. Primroses are a good example.
• Flowers: Flowers are a perennial’s reproductive structure.  ....read more