In its first year, the biennial plant undergoes primary growth, during which its vegetative structures (leaves, stems, and roots) develop. Usually, the stem of the plant remains short and the leaves are low to the ground, forming arosette. After one year's growing season, the plant enters a period ofdormancy for the colder months. Many biennials require a cold treatment, orvernalization before they will flower.[3] During the nextspring orsummer, the stem of the biennial plant elongates greatly, or "bolts".[4] The plant then flowers, producingfruits andseeds before it finally dies. There are far fewer biennials than eitherperennial plants orannual plants.[5]
Biennials do not always follow a strict two-year life cycle: plants in the wild can take three or more years to mature. Rosette leaf size has been found to predict when a plant may enter its second stage of flowering and seed production.[6] Alternatively, under extreme climatic conditions, a biennial plant may complete its life cycle rapidly (e.g., in three months instead of two years).[7] This is quite common in vegetable or flower seedlings that werevernalized before they were planted in the ground. This behavior leads to many normally biennial plants being treated as annuals in some areas. Conversely, an annual grown under extremely favorable conditions may have highly successful seed propagation, giving it the appearance of being biennial or perennial. Some short-lived perennials may appear to be biennial rather than perennial. True biennials flower only once, while many perennials will flower every year once mature.
The Sweet William Dwarf plant is a biennial plant.
Biennials grown for flowers, fruits, or seeds are grown for two years, whereas those grown for edible leaves or roots are harvested after one year—and are not kept a second year to run to seed.
^Gross, Ronald S.; Werner, Patricia A. (1983). "Probabilities of Survival and Reproduction Relative to Rosette Size in the Common Burdock (Arctium minus: Compositae)".American Midland Naturalist.109 (1): 184.doi:10.2307/2425529.JSTOR2425529.
