Flowering plants that grow in temperate climates and take two years to complete their biological life cycle are known as biennial plants. The biennials that are grown for seeds, fruits and flowers are grown for two years, whereas those for edible roots and leaves are grown for one year only.
Examples of biennials include: parsley, fennel, onion, cabbage, silverbeet and carrot.
Life Cycle of Biennials
In the first year of its life cycle, a biennial plant shows primary growth where it develops stems, leaves and roots. The stem is short and the leaves are also borne closer to the ground in the form of a rosette.
After this development, the plant goes dormant in the winters. Many biennials require vernalisation or cold treatment for flowering. In the next spring and summer season, the stem elongates and the plant finally produces flowers and fruits before its death. There are much lesser biennial plants found as compared to annuals and perennials.
Biennial plants do not always follow a 2 year life cycle. Those that are found in the wild can take upto 3 years to mature fully. The rosette leaf size of the plant can be analysed to find out if the plant will flower for a second year.
If a biennial is vernalised before planting, they can quickly complete their life cycle in 3 months. This technique is applied to treat biennials as annuals in some areas. On the other hand, if an annual is grown under extreme favourable conditions, it shows successful seed propagation and can be treated as biennials or perennials.
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