Plants can be classified according to the lenght of their life cycle into three categories: annuals, biennials, and perennials. Understanding the difference between these categories is helpful when planning and tending to your garden.
Annuals
Annuals are herbaceous plants that complete their life cycle within a short period of time. They germinate, grow, flower, produce seeds, and then die, all within the space of a year.
Annuals need to be replanted or sown every year. However, many annuals naturally reseed as long as all the dead flower heads aren’t removed and that there are areas in the garden beds that are cleared of mulch. Some examples of self-seeding species are cornflowers, spider flowers, corn poppies, cosmos, and love-in-a-mist.
The main appeal of annuals is their long flowering period, with many blooming all summer long and some even up until the first frost.
Biennials
Biennials are herbaceous plants with a two-year life cycle. In the first year, biennials only put out leaves. In the second year, they produce flowers and fruit, before dying. Some examples are purple foxglove, silver mullein, honesty, and Miss Willmott’s ghost.
Biennials often have a long flowering period and can reseed themselves naturally.
Did you know? Onions, beets, carrots, turnips, parsley, and many other plants commonly found in vegetable gardens are biennials! They are usually grown as annuals, unless you collect their seeds.
Perennials
In botanical terms, perennials are herbaceous or woody plants (like trees or shrubs) that live for many years.
In horticulture, the term “perennial plant” is more commonly used to refer to herbaceous plants that are hardy within the climate they are growing in and that live for many years.
Perennial plants can survive the winter thanks to their underground organs (roots, bulbs, tubers, and rhizomes). These plants go dormant in the fall and resume their growth in the spring. With the exception of certain species, the leaves of most perennials die back in winter.
Some examples of perennials are coneflowers, daylilies, asters, and rhubarb.
Perennials tend to require less care than annuals and biennials but have a shorter flowering period. Still, some perennials can flower for four to six weeks, or even up to three months, like lesser calamint (Clinopodium nepeta).
Perennials grown as annuals
Many plant species that are sold as annuals in our climate are actually perennials from tropical or subtropical regions. This is true for garden impatiens, petunias, geraniums (Pelargonium sp.), tomatoes, and eggplant. These plants are often called tender perennials, and some can be overwintered indoors as plants or cuttings.
Short-lived perennials
Some perennials, called short-lived perennials, only live for a few years. Though these perennials sometimes only live two or three years, they are not biennials, as they are able to produce flowers and seeds more than once before they die. Many short-lived perennnials reseed spontaneously.
Some examples of short-lived perennials are columbines, blanket flowers, mallows, and blue vervain.
Planting perennials, biennials, and annuals together in garden beds is a great way to enjoy their complementary and unique traits. You’ll enjoy varied, colourful flower beds from spring through fall.