An Introduction to Biennial Plants

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This article in as introduction to biennal plants
by Brett · All Zones · Biennial Plants · 2 Comments · February 01, 2011 · 6,718 views

A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots, then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming a rosette. Many biennials require a cold treatment, or vernalization, before they will flower. During the next spring or summer, the stem of the biennial plant elongates greatly, or "bolts." The plant then flowers, producing fruits and seeds before it finally dies. There are far fewer biennials than either perennial plants or annual plants.

Under extreme climatic conditions, a biennial plant may complete its life cycle in a very short period of time (e.g. three or four months instead of two years). This is quite common in vegetable or flower seedlings that were exposed to cold conditions, or vernalized, before they were planted in the ground. This behavior leads to many normally biennial plants being treated as annuals in some areas.

From a gardener's perspective, a plant's status as annual (completes life cycle in one year), biennial, or perennial (lives 2 or more years) often varies based on location or purpose. Biennials grown for flowers, fruits, or seeds need to be grown for two years. Biennials that are grown for edible leaves or roots are grown as annuals, e.g. beets, Brussels sprouts, cabbage, carrots, celery, lettuce, parsley, and Swiss chard. If a normally biennial plant is grown in extremely harsh conditions, it is likely to be treated as an annual because it will not survive the winter cold. Conversely, an annual grown under extremely favorable conditions may have highly successful seed propagation, giving it the appearance of being biennial or perennial. Some short-lived perennials may appear to be biennial rather than perennial. True biennials flower only once, while many perennials will flower every year once mature. Many consider some biennials as perennial because they reseed themselves (self-sow) after flowering in the garden. From these seeds will come a new crop.

Examples of biennial plants:

  • Sweet Williams
  • Evening Primrose
  • Foxglove(pictured above right)
  • Black-eyed Susan
  • Viola
  • Queen Anne's Lace
  • Parsley
  • Lunaria
  • Silverbeet
  • Colic Weed
  • Carrot

Plants related to 'An Introduction to Biennial Plants':



Joyce Joyner

Joyce Joyner · Gardenality Sprout · Zone 8A · 10° to 15° F
I agree with this article...LOL....maybe they will, maybe they won't.....I now consider them short-lived perennials in my garden.....in the past I had very good luck with foxglove reseeding but in the past few years it has been minimal or nonexisistant...I was wondering if it was too much hybidizing?

10 years ago ·
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Gardenality.com

Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F
It might depend on the variety of the foxglove (Digitalis) and/or weather conditions and soil type. If the weather is dry, and the soil dry or hard-packed, the seed might not germinate? I haven't had much luck with reseeding biennials. Probably because I never deep till entire areas where I plant them. Most of the time, when planting perennials and biennials in a garden, I prefer digging individual holes for individual plants rather than tilling the entire garden bed. This helps to keep plants known to be invasive in bounds and smaller in size. In my garden, the space between plants is usually just regular old Georgia clay/dirt, which isn't a good seed bed.

10 years ago ·
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