Definition - What does Biennial mean?
Biennial plants produce only foliage during their first year. During the plant’s second year of life, it produces flowers, develops seeds, and then dies. Its entire life cycle only lasts two years.
After a biennial dies, only the seed remains to produce a new plant and begin its own two-year life cycle that will culminate in its own the production of seeds.
A biennial plant is in contrast to an annual plant, which has a life cycle of only one year. There are also perennials, which live for more than two years. They can either be short-lived (only a few years) or long-lived.
MaximumYield explains Biennial
In the biennal's plant’s first year of life, its seed germinates into a seedling. The seedling grows strong roots, stems, and foliage. In the second year of life, the plant will produce flowers, the flowers will be fertilized, and produce viable seeds. Upon completion of the seed production, the plant will die and shed its seeds.
Some biennial plants must experience a period of cold between their first year of growth and their second year in order to flower and produce seeds. Without a chill period, the plant will fail to bloom or seed.
Growers can force a biennial plant that requires vernalization to complete its entire life cycle in less than a year by manipulating its exposure to cold. This is done to force the plant to produce flowers in the first year of growth. Such a practice basically turns a biennial plant into an annual.
Other deciding factors such as periods of drought or excessive heat can also shorten a biennial's natural life cycle. Some biennials also only grow as annuals in areas with overly severe winters. Beets, Brussel sprouts, hollyhocks, foxgloves, Swiss chard, onions, lettuce, and evening primrose are all biennials.