Biennial Plant Information: What Does Biennial Mean

One way to categorize plants is by the length of the plant’s life cycle. The three terms annual, biennial and perennial are most commonly used to classify plants due to their life cycle and bloom time. Annual and perennial is fairly self explanatory, but what does biennial mean? Read on to find out.

What Does Biennial Mean?

So what are biennial plants? The term biennial is in reference to the plant’s longevity. Annual plants live just one growing season, performing their entire life cycle, from seed to flower, in this short period of time. Only the dormant seed is left to cross over into the next growing season.

Perennial plants live three years or more. Usually, the top foliage dies back to the ground each winter and then regrows the successive spring from the existing root system.

Basically, biennials in the garden are flowering plants that have a two-year biological cycle. Biennial plant growth begins with seeds that produce the root structure, stems and leaves (as well as food storage organs) during the first growing season. A short stem and low basal rosette of leaves form and remains through the winter months.

During the biennial’s second season, biennial plant growth completes with the formation of flowers, fruit and seeds. The stem of the biennial will elongate or “bolt.” Following this second season, many biennials reseed and then the plant usually dies.

Biennial Plant Information

Some biennials require vernalization or cold treatment before they will bloom. Flowering may also be brought about by the application of gibberellins plant hormones, but is rarely done in commercial settings.

When vernalization occurs, a biennial plant may complete its entire life cycle, from germination to seed production, in one short growing season — three or four months instead of two years. This most commonly affects some vegetable or flower seedlings that were exposed to cold temperatures before they were planted in the garden.

Other than cold temperatures, extremes such as drought can shorten the biennial’s life cycle and compress two seasons into a year. Some regions may then, typically, treat biennials as annuals. What may be grown as a biennial in Portland, Oregon, for example, with a fairly temperate climate, would likely be treated as an annual in Portland, Maine, which has far more severe temperature extremes.

Biennials in the Garden

There are many fewer biennials than perennial or annual plants, with most of them being types of vegetables. Keep in mind that those biennials, whose purpose is for flowers, fruits or seeds, need to be grown for two years. Climatic conditions in your area which are unseasonably cold, with lengthy periods of frost or cold snaps, affect whether the plant will be a biennial or an annual, or even if a perennial appears to be a biennial.

Examples of biennials include:

  • Beets
  • Brussels sprouts
  • Cabbage
  • Canterbury bells
  • Carrots
  • Celery
  • Hollyhock
  • Lettuce
  • Onions
  • Parsley
  • Swiss chard
  • Sweet William

Today, plant breeding has resulted in several annual cultivars of some biennials that will flower in their first year (like foxglove and stock).

Annual, Perennial, Biennial?

Annuals – Plants that perform their entire life cycle from seed to flower

Annual Plains Coreopsis

to seed within a single growing season. All roots, stems and leaves of the plant die annually. Only the dormant seed bridges the gap between one generation and the next.

Perennials – Plants that persist for many growing seasons. Generally the top portion of the plant dies back each winter and regrows the following spring

Perennial Purple Coneflower

from the same root system (e.g. Purple Coneflower). Many perennial plants do keep their leaves year round and offer attractive borders and groundcover (e.g. Tickseed, Shasta and Ox-Eyed Daisy). NOTE: WHEN STARTING PERENNIAL PLANTS FROM SEED, BLOOMS WILL BE OBSERVED IN EITHER THE SPRING OR SUMMER OF THE SECOND YEAR AND EACH YEAR THEREAFTER (e.g. Ox-Eyed Daisy planted in the spring of 1996 will not bloom until the spring of 1997).

Biennials – Plants which require two years to complete their life cycle.

Biennial Foxglove

First season growth results in a small rosette of leaves near the soil surface. During the second season’s growth stem elongation, flowering and seed formation occur followed by the entire plant’s death.

Annual/Perennial – A plant can behave as an annual or a perennial depending on local climatic and geographic growing conditions. In the southern portion of the United States, these plants tend to grow much quicker than in the north due to the warmer weather and extended growing season. For example: a Black-Eyed Susan would behave as an annual if grown in Louisiana; whereas, if grown in Ohio, a Black-Eyed Susan would behave as a perennial.

Plants are basically categorized into three groups based on their life cycles: annuals, perennials and biennials. Knowing which plants are which type can help you anticipate your needs for planning vegetable and flower gardens.


Plants are basically categorized into three groups based on their life cycles: annuals, perennials and biennials. Knowing which plants are which type can help you anticipate your needs for planning vegetable and flower gardens.

Annuals experience their entire life cycle within a single growing season. Every part of the plant dies annually, including leaves, roots and stems. Before the plant dies, it goes to seed. While the seed may grow on its own and start a new cycle, the originally plant is gone in an annual timeframe.

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  • Examples: many grasses, marigolds, petunias, zinnias, corn, wheat, peas, beans, lettuce, rice

Perennial plants live for several growing seasons. Generally the leaves and stems die at the end of the season and the root remains alive through the winter. In spring, the root system produces new flowers or fruit. Many perennial plants keep their leaves all year and make attractive landscape plants. When planting perennial plants from seed, keep in mind that they will not bloom until the second year.

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  • Examples: asparagus, artichokes, rhubarb, leeks, eggplants, most fruit trees, most herbs

Biennial plants have a two-year lifespan. They behave like a perennial for the first season, dying back and regrowing from the root. During the second season, the plant flowers and goes to seed. At the end of the second season, the entire plant dies.

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  • Examples: carrots, celery, parsley

Where the classifications of annual and perennial get tricky is with different climates. Plants that are generally annuals may behave like perennials in warmer climates because they don’t experience temperatures that normally signify the end of their season, and are known as tender perennials, including tomatoes and peppers. Biennials grown in cool climates generally experience the life cycle of an annual.

Plant types are grouped by the growing seasons required to complete a life cycle. In general, plants are classified as Annual, Biennial, Perennial, or Ephemeral. Factors that determine the classification of a plant include location, reproduction, and environmental roles. The harvest times for most produce varies depending upon environmental factors.

Annual plants

Are those whose life cycle is completed over a year’s time. Annuals are usually planted in the spring, bloom in the summer, and seed just before their demise in the fall. Annuals can be separated into three additional groups based on the environmental temperatures in which they can thrive. These groups are:

• Hardy Annuals – which are able to withstand cold soil and hard frosts,

• Half – Hardy Annuals – which are still able to thrive in cold soil temperatures to a certain limit, and can usually withstand light frosts.

• Tender Annuals – cannot survive in freezing temperatures whatsoever.

Most vegetable and grain plants are annuals, but not all. Examples include Potatoes, Tomatoes, Broccoli, Cauliflower, and Melons.

Bush of peas

Biennial plants

Complete their life cycle over a two year growing period. Once sown, vegetative structures such as leaves, stems, and roots begin to grow and form a small rosete. Biennial plants will only produce these structures during the first year. After the first growing season, the tops of the plants will die back, leaving rootstock that will remain during the plant’s dormancy through the colder months. In the following growing season of the second year, biennials will flower, set seed, and finally complete their life cycle and perish in the fall of the second year. Examples of biennial plants include Beets, Cabbage, Carrots, Hollyhocks, Parsley, and Foxglove.

An interesting thing to know about Biennials is that, dependant upon the climate, they can be, and sometimes are grown as Annuals.

Conditions such as rainfall, soil temperature, and location cause these plants to alter their life cycle. Generally, biennials exposed to cold temperatures early in their growth may produce seed in the first year.

Some biennial plants are also grown for their vegetable parts, and therefore harvested in the first growing season. Carrots, for instance. If carrots are left in the ground, they will flower the next growing season and produce seed. By this time, however, the vegetable will have taken on a bitter flavor. Other examples of true Biennials treated as annuals are Garlic, Cabbage, and Celery.

Organic Carrots

Perennials

Are plants that live more than two years. Perennials are a bit more complicated in their classifications, as there are many factors that affect their life cycles and habits. In general, perennials can be very cold hardy, and live longer than annuals and biennials. Perennials vegetative reproductive structures allow them to return and thrive from one year to the next without seeding. These structures include bulbs, rhizomes, tubers, and crowns.

There are two groups of perennial plants; herbaceous and woody.

•Herbaceous, or deciduous perennials bloom in the growing season and die back in the fall and winter. During this time, the top foliage of the plants will perish while the rootstock remains from which the plant will bloom again in the spring. Examples of herbaceous perennials are Rhubarb, Strawberry, Asparagus, and Blueberries.

•Woody, or evergreen perennials are plants whose top growth persists throughout winter, and continues to grow larger during the spring and summer. Many trees, vines, shrubs and herbs exist within this group, including Hydrangeas, Azaleas, Peony, Apple and Pear trees, Mint, and Fennel.

Red apples in an orchard

Finally,

Ephemeral plants

Are likely the most unique and complicated classification of plants. Ephemeral plants live extremely short life cycles with specific requirements, and are broken down into three groups: Spring, Desert, and Weedy. Ephemeral plants live in less than ideal growing conditions, and have adapted to take advantage of short lasting, perfect conditions for growing. Ephemerals germinate, bloom, seed, and die all within a few weeks. The seeds they leave behind are very resilient to drastic climate changes, and lay dormant until optimal conditions once again appear.

• Spring ephemerals are, essentially, perennial plants and flowers, whose life cycles are shortened by climate. These plants typically live deep within woodlands, and their life cycle is determined by the shade of the surrounding trees. These plants sprout early in spring, and bloom and seed shortly afterward before the trees above begin to leave and shade the forest floor. With the shade, the leaves of the plants will wither and die, and the rootstalk remains as the plants become dormant until the next growing season. Examples of spring ephemerals are Ferns, Witch Hazel, and Dogwood.

• Desert ephemerals have adapted to the harsh climate of desert land. The seeds of these plants have a very low metabolism, and require little water. This enables them to survive the dry season. Once the brief wet season arrives, desert ephemerals spring up quickly, stay small, reproduce, and die, all within a few days. Cinchweed, Thale Cress, and Pale Madwort are all examples of desert ephemerals.

• Weedy ephemerals are agricultural weeds that depend on human disturbance, such as ploughing, for germination. As the soil becomes disturbed, aeration is improved, and surface light again becomes available. Weedy ephemerals grow and reproduce very quickly, and yield high amounts of seed. This group includes Hairy Bittercress, Chickweed, and Groundsel.

Annual plants live for one growing season and then die, while perennials regrow every spring. The difference is genetic, and yet, a clever “plant gene therapy” technique can be used to change an annual into a perennial.

In 2008, scientists with the Flanders Institute for Biotechnology in Gent, Belgium, determined what makes plants either annual or perennial. The difference, according to plant geneticist Siegbert Melzer and his team, comes down to two critical flower-inducing genes that, when turned off, can make an annual plant regrow every year.

The rapid growth of flowers, and then seeds, is the strategy most annuals use to propagate from one generation to the next and one growing season to the next. Annuals experience “rapid growth following germination and rapid transition to flower and seed formation, thus preventing the loss of energy needed to create permanent structures,” the researchers explained in a press release.

“They germinate quickly after the winter so that they come out before other plants, thus eliminating the need to compete for food and light,” according to the statement. “The trick is basically to make as many seeds as possible in as short a time as possible.”

Perennials instead build “structures” such as overwintering buds, bulbs or tubers, that contain cells that are not yet specialized and, when the next growing season begins, can be converted into stalks and leaves .

An annual uses up all of its non-specialized cells making flowers, and thus, after dropping seeds, it dies. The growth of the flowers is triggered by the plant sensing the length of day and amount of sunlight. When the light is just right, “blooming-induction genes” are triggered.

By deactivating two of the genes that induce flower growth in the thale cress, a flowering plant whose genome has been entirely sequenced, the researchers created mutant plants that “can no longer induce flowering, but … can continue to grow vegetatively or come into flower much later.” Because the plants don’t use up the store of non-specialized cells making flowers, they become perennials, able to continue to grow for a long time.

And, like true perennials, the altered annuals show secondary growth with wood formation.

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