What Is an Annual – Biennial – Perennial?

The day I took my grandson (then a second or third grader) to the garden to show him the sensitive plant (Mimosa pudica) and its reactions to the touch of one’s hands, I was greatly surprised to have him ask: “Is it a perennial or an annual?”

It was satisfying to know that youngsters were being taught these plant lessons in school. My answer was that it was an annual. I doubt that I could have held his interest long enough at that time to explain fully but I should not have said, without qualifying my statement, that the sensitive plant is always an annual. Here it has all the characteristics of an annual but in warmer climates it may be perennial.

mimosa pudica

We find this true about other plants whether annuals, biennials, or perennials. We can and do classify them but some do not always follow exactly the traits of that particular group in which they have properly been placed. True annuals complete their growth in a single year. The seeds germinate, the plants grow, bloom, produce a seed crop, and die – completing a life cycle in one year or less. Cosmos, cockscomb, and marigolds are examples.

Perennials have the ability to live for a number of years. This includes such woody plants as trees, shrubs, and some of the vines but when a gardener uses the term he usually has in mind only the hardy herbaceous plants – non-woody plants such as platycodon, columbine, or peonies. Their tops die in winter (except for a few evergreen kinds) but the plants continue to exist because their underground parts remain alive. The tops arc renewed each spring by the live roots. In the case of an annual, the entire plant dies at the end of the first season.

Perennials like the peony, bleeding heart, and dictamnus seem almost to endure forever without special attention but these are exceptions. Many perennials need dividing by the third year if they arc to persist and remain attractive. Iris is a good example. It spreads, makes new growth which sends up the flower stems while the center of the plant dies out.

A true biennial produces only a rosette of leaves the first year. It blooms and makes seeds the second year and then dies, root and branch. Occasionally weather conditions or too late planting may prevent the plant from making enough growth to bloom the second year. It may Then live over another season before it blooms and dies a natural death. Gilia rubra which is found through a large part of central Texas has been found to remain in its rosette stage for as much as five or six years during prolonged drouth before the plant has strength to send up a blossom stem. In my own garden I have had plants of the biennial canterbury bells remain as rosettes for two years, waiting until the third year to bloom.

Some hollyhocks bloom the first year following the pattern of a true annual – others may make only a crown of leaves and wait for blossoms until the second year, and then die as a biennial, or make new growth and live over and bloom for several more years in which state they could be classed as perennials. Penstemons are classed as perennials but in our gardens we find that some varieties perform exactly as biennials. In some instances, preventing seed formation will make them live over.

The seeds of hardy annuals can be sown in the early spring as soon as the soil can be worked, or even very late in the fall. These cannot endure winter temperatures after they are up but arc able to take what frost may occur after germination in the spring. Among these we can include sweet peas, poppies, and sweet alyssum.

Seeds of half-hardy and tender annuals such as torenia, Cobaea scan-dens, and love apples are started early in flats in the house. Seeds cannot be planted outside until danger of frost is over and then the season is not always long enough for them to do their best.

Among the evergreen perennials (those that retain their leaves during the winter) are: heuchera (coral bells), sedum, and yucca. Among the perennials that bloom the first year as annuals but do have the ability to live on after blooming are platycodon, some of the carnations, and hardy candytuft (Iberis sempervirens, also an evergreen perennial). Tender or half-hardy perennials that bloom the first year from seeds but are not winter hardy must be grown as annuals or carried over in storage during winter. Examples are southern star (Oxypetalum coeruleum), dahlias, and four-o’clocks (Mirabilis jalapa).

Short-lived perennials such as basket of gold (Alyssum saxatile), peach-leaf campanula (Campanula persicifolia), and heuchera must be kept going by taking cuttings periodically, or starting new plants from seeds. Although rightly considered true perennials they have a tendency to die out after a few years.

Sweet Rocket (Hesperis matronalis) and woad (Isatis glauca) are both perennials and bring abundant color to the early garden. They self-sow very freely and because the old plants become rather woody and unsightly, these perennials are better if treated as biennials by removing the old plants after blooming, and letting the vol unteer seedlings grow for blossoms the next spring.


All this may sound complicated and confusing because the differences among the three groups are often not sharp and distinct. Too, it may appear relatively unimportant as to whether one knows if plants are annuals, biennials, or perennials, or perhaps fit into several classes. But there are many occasions when it would be a great help to be familiar with a plant’s classification in order to know what can be expected from it. We can hardly make out a garden order without knowing. Seed and nursery catalogs are good reference books for most of them have the various items listed under sections such as annuals, perennials, or biennials, or have symbols of some kind which enable one to tell easily where each belongs.

If we desire something that will give quick results we must know to turn to the annual section or to those perennials that bloom the first year. If we are especially fond of the lovely canterbury bells and want them every year we must realize that they are biennial, and so should plant seeds or buy plants annually. If we plant dahlias we must know that they are a tender perennial and must be dug and stored in the fall if we wish to have them for another year.

There are dozens of reasons why we should know these things. Last but not least, perhaps one of the important reasons for knowing is to be able to answer the question of an 8-year old when he asks, “Is it a perennial or an annual?”

Tips To Improve Your Plant Care
Sign Up For My Free Daily Newsletter

We will never share your email address period.

{ 0 comments… add one now }