What Are Biennial Plants?

biennial-plants Credit: Toshiyuki IMAI/CC-BY-2.0

Biennial plants are plants that takes only two seasons or 2 years to complete their life cycle. Some of the more popular biennial plants include the onion, parsley, silverbeet, cabbage, Lunaria, common mullein, Black-eyed Susan, colic weed, carrot, California poppy, forget-me-not, poppy, Sweet William, some hollyhock species, stock and foxglove.

When exposed to extreme weather conditions, some biennial plants will have a shorter life cycle. For example, a biennial plant that is exposed to extreme cold may have a life cycle of only 3 months instead of 2 years. This common occurrence has led some people to consider a typical biennial plant as an annual plant in some locations.

The first season of biennials is marked by the growth of a small rosette of leaves near the soil as well as its stem and roots. It stops growing at the onset of the cold months. During its second year a biennial plant will grow a longer stem and start sprouting flowers that develops into seed-bearing fruits before dying off.

Biennial plants that are cultivated for their edible roots or leaves are treated as annuals and are harvested each season. Those that are cultivated for their flowers, fruits or seeds needs to be grown for their full life cycles.