Biennial plants have a two year life cycle; roots, stems and leaves in the first year with flowers following the next year after a cold winter dormant period. Biennials will produce seed and fruit before dying. There are not as many biennial plants as there are perennials or annuals.
Biennial plants, when exposed to extreme climate conditions, may have a shortened life cycle of a few months especially if the plants were exposed to colder than normal temperatures. Most biennials can be planted as annuals. Some biennials have been genetically altered to produce a flower in the first year from seed.
Carrot, onion, parsley, Sweet William, and hollyhocks all produce seed in the second year making them a biennial. For instance, the carrot must be harvested (or over wintered in a protected area) and then replanted the following year to produce carrot seeds.
Image Caption: Sweet William Dwarf. Credit: AutoGyro/Wikipedia (CC BY-SA 3.0)