Raffi at 14:31, 4 April 2007

2007-04-04T14:31:55Z

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[[Image:Parsley Curled.jpg|right|thumb|200px|[[Parsley]] is an example of a biennial plant.]]

A '''biennial plant''' is a flowering [[plant]] that takes between twelve and twenty-four months to complete its [[Biological life cycle|lifecycle]]. In the first year the plant grows leaves, stems, and roots (vegetative structures); 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. The next spring/summer the stem of the biennial plant elongates greatly, or [[Bolting|bolts]]. The plant then [[flower]]s, producing [[fruit]]s and [[seed]]s before it finally dies. There are far fewer biennials than either [[perennial plant|perennial]]s or [[annual plant|annuals]].

Under extreme climatic conditions, a biennial plant may complete its lifecycle in a very short period of time (e.g. 3 or 4 months instead of 2 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 behaviour leads to many normally biennial plants being treated as [[annual plant|annuals]] in some areas.
Flowering can be induced in some biennials without vernalization by application of the [[plant hormone]] ''[[gibberellin]]'' but it is rarely done commercially.

From a gardener's perspective, a plant's status as [[annual plant|annual]], biennial, or [[perennial plant|perennial]] 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. [[beet]], [[Brussels sprouts]], [[cabbage]], [[carrot]], [[celery]], [[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 favourable conditions may have highly successful seed propagation that it gives 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.

Examples of biennial plants are [[parsley]], ''[[Lunaria]]'', [[silverbeet]], [[sweet William]], [[colic weed]], and [[carrot]]. [[Pansy]] is a biennial often grown as an annual. Plant breeders have produced annual cultivars of several biennials that will flower the first year from seed, e.g. [[foxglove]], [[Matthiola incana|stock]], and [[hollyhock]].

Biennials may be kept alive longer than two years under environmental conditions that prevent them from flowering. Biennial [[sugar beet]] was prevented from flowering by not giving it the vernalization required for flowering. It was kept alive in a greenhouse for 41 months.<ref>Salisbury, F.B. and Ross, C.W. 1985. ''Plant Physiology.'' Belmont, CA: Wadsworth.</ref>

==References==
<references/>

==External links==
* [http://www.orst.edu/extension/mg/botany/cycles.html Plant life cycles]

[[Category:Plants]]
[[Category:gardening]]

Biennial plant - Revision history

Raffi at 14:31, 4 April 2007