A biennial is a plant that normally requires two growing seasons to complete its life cycle.

 

Biennials do not flower in the first season of their growth, but flower and bear fruit in the second season, and then die. A familiar example is the common foxglove (Digitalis), shown here.

 

Many cultivated plants are biennials, including the carrot, turnip, parsnip, parsley, and celery, as are many garden flowers, such as stock, wallflower, and honesty. But plants which in ordinary circumstances are biennials, often become annuals when early sowing, warm weather, or other causes promote the earlier development of a flowering stem. If, on the other hand, the flowering of the plant is prevented – or, in many cases, if it is merely prevented from ripening its seed – it will continue to live for a much longer period; the same bed of parsley, if regularly cut over, will remain productive for a number of years (i.e., it will be a perennial), while a normally annual plant may be kept growing for two years or more if its flowering is carefully prevented.