Plant Terminology: Annuals, Biennials, Perennials
Annual, perennial, biennial – these important terms refer to a plant’s life cycle or life span, which usually includes the production of flowers and seeds that guarantee the next generation. They’re important for gardeners to understand if they’re to choose plants wisely. Although the distinctions are occasionally blurred, for the most part you can refer to the following definitions.
Annuals: Live For One Season
Annual plants complete their life cycle in one growing season. Zinnias, for example, sprout from seeds in spring, produce foliage, and then begin flowering. By late summer these flowers, if left on the plant, go to seed — that is, they mature into a seed-head filled with viable seeds. The mother plant dies with the first frost, but she’s produced hundreds or even thousands of seeds capable of carrying on the next generation. The same holds true for beans. If we don’t harvest them, the seeds will mature within the pods.
Biennials: Live for Two Years
These intriguing plants live for two seasons. In their first season, the seeds sprout and the plant produces only foliage, and then overwinters. The next spring, it sprouts to life and produces flowers and mature seed, after which the plant dies. Some of our favorite vegetables are biennials. In its first season a carrot plant develops a deep, carbohydrate-filled taproot to store energy needed to survive winter. If left unharvested, the plant will re-sprout in spring, produce flower and seeds, and then die back. Cabbage, kale, and celery are also biennials, as are Canterbury bells and many foxgloves.
Perennials: Live for Three or More Years
Defined as plants that live for three or more years, perennials vary in their life spans. Some perennials are described as short-lived. An individual columbine plant, for example, may live for several years and then begin to die back. However, in that span it has produced plenty of seed. Peonies and daylilies, on the other hand, are long-lived, lasting for a decade or longer if given ideal growing conditions.
Self-Sowing Annuals: Reseed Themselves
Some annuals behave like perennials, in that they appear to return year after year. However, each year brings a new generation of plants that have grown from seeds dropped by the mother plant, which died at the end of the previous growing season. This tendency is also referred to as self-seeding or reseeding. Calendula and cornflower are two self-sowing annuals. When a plant shows up in a different spot in the garden, the seed having been carried by an insect, animal, or the wind, the surprise plant is sometimes called a volunteer.
Half-Hardy Annuals: Tolerate Light Frosts
Unlike zinnias and marigolds that need warm temperatures, some annuals will sprout in early spring and continue growing into fall, tolerating frosts and even light freezes. They’ll be killed back by a prolonged or deep freeze. Examples include sweet peas and snapdragons.
Temperennials: Perennial in Warmer Regions
Although it’s not widely used, the term temperennial makes an important distinction. It describes plants that are perennial in their native habitat, often tropical or semi-tropical, but are grown as annuals in colder regions. Some temperennials, such as cannas, are hardy to regions as cool as zone 8. Elsewhere, the roots must be dug up and overwintered in a sheltered spot. Peppers, tomatoes, and eggplants are all perennials, as are many petunias and the bright red geraniums (Pelargonium species) sold alongside the annuals. They can all be grown year-round in frost-free areas, or overwintered indoors in cooler locales.
Woody Plants: Yes, They're Perennials, Too
What about trees and shrubs? Plants that produce woody stems are, technically speaking, perennials, because they live for three or more years. However, we usually reserve the term perennial for herbaceous (non-woody) plants.
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