A biennial plant is a plant with a two-year growing cycle. Depending on the climate a plant grows in and other factors, the cycle may be completed in more or less time. Plants that complete their cycle in less than two years in some climates may be treated as annuals for the purposes of gardening in these regions, while plants with a more extended lifecycle may be closer to perennials from a gardening perspective. A wide range of plants are considered biennials and can be obtained at nurseries and garden supply stores.
The typical biennial plant starts growing in the spring of the first year, developing vegetation and a root system. Depending on the plant, it may spread out to cover ground, opt to stay highly compact, or grow in a shrublike pattern. As the weather gets cooler in the fall, the vegetation dies back and the plant goes into dormancy. In the following year, the biennial plant produces flowers, going to seed in the summer and dying off once the seeds have been distributed.
Many biennial plants are popular because they reseed themselves. Once a gardener manages to establish a bed of plants, they will continually renew. Plants at different stages in their life cycle will keep the flowerbed continually green and flowering and will also limit the spread of weeds, making less work for the gardener. A biennial plant may also be grown from cuttings in some cases, for gardeners interested in creating clones of parent plants.
One advantage to biennial plantings is that they can be continually changed and renewed to keep a garden more visually interesting. Gardeners can use plants that do not reseed themselves readily, or be aggressive about removing plants before they get a chance to go to seed, clearing the bed to establish a new group of plants. Biennials come in a range of styles, from plants that lend themselves well to very formal gardens to more leggy, wild-looking plants, such as hollyhocks, that can be used for informal gardening.
Because the life cycle of a plant varies by climate, gardeners should not assume that something labeled as a biennial plant will be truly biennial. It is advisable to ask employees at a garden store for information about specific plants of interest, or to consult other gardeners about what they are growing and how plants perform in their gardens. People who are interested in specific plants they see in the neighborhood can ask gardeners if seeds and cuttings are available.