What Are Perennials?

Wondering if perennials are right for you? Dig into a perennial definition to learn more about these garden favorites. Most gardeners are familiar with annuals, courtesy of the colorful flats of marigolds, petunias and pansies at garden centers and box stores. Annuals create a showy display that’s tough to miss. Perennials, on the other hand, are often sold as green plants or a few stems in a large pot. Once you define perennials and understand their nature, you might find you’re eager to learn more about them. 

In the purest sense, the definition of perennials comes down to understanding a plant’s life cycle. Plants are genetically wired to reproduce—to set seed. This is why one dandelion flower turns into a puffball with hundreds of seeds. 

Annuals accomplish their reproduction, or life cycle, in one growing season. Consider zinnia, an annual. Plant zinnia seed in late spring, and the seed sprouts and produces a plant. The plant flowers and, if frost doesn’t arrive too early, the flowers die—filled with viable seeds. The plant dies with frost. When all of this takes place in one growing season, that plant is an annual. 

The definition of perennial embraces plant reproduction along with form. Try this for a working perennial definition: a plant that lives for more than two years, producing seed each year. Perennials usually die back to the ground with frost, but resprout from roots or stems in spring. Where annuals do their thing in one growing season, perennials are the original come-back kids, returning to grace the garden with beauty year after year. 

Most perennials are non-woody plants, meaning they don’t have woody stems like a shrub or rose. Some perennials, however, can develop woody stems over the course of a growing season. Russian sage plants and most types of lavender develop woody stems during a growing season. In cold regions with freezing winters, these stems die back over winter. In spring, these perennials must be pruned to a shorter height of 6 to 12 inches. After mild winters, buds on the woody stem remains sprout; after hard winters, new growth emerges from the plant’s roots. 

Many garden catalogs and books tout perennials as forever plants. By comparing annuals and perennials, they show that annuals must be planted every year, while perennials come back new each spring. The reality is that most perennials live an average of seven years. Some perennials, like stokes aster and blackberry lily, are short-lived, lasting only a few years. Other perennials, like peony and hosta plants, can survive many years in the garden. 

Unlike annuals, which flower non-stop until frost, many perennials have a specific bloom time. Flowers appears during this window and then stop. The rest of the growing season, a perennial’s leaves create food that’s shuttled to plant roots where it’s stored as reserves to fuel next year’s growth cycle. When designing a garden with perennial plants, part of the fun is mixing and matching perennials that flower at different times to create a steady supply of blooms.