Plant Life Cycles and Hardiness
By Emily Rose Alworth, Horticulturist
Garden plants can be categorized by their hardiness, growing cycle, and lifespan. Each plant has a range of conditions that it can tolerate, some are more flexible than others.
Each plant has different temperature requirements to complete its life cycle. Plants can be hardy yet unable to flower, fruit, or set seed if the duration of exposure to ideal temperatures is not sufficient. This means that zone pushing plants outside of their normal climate may not result in the full seasonal changes they display in their natural habitat.
Learn more about the USDA Plant Hardiness Zones and American Horticultural Society Heat Zones here.
Annuals, Perennials, and More!
Annuals
Annual plants have a short life cycle that completes within a single year; growing from seed, flowering, fruiting, and dying. These plants are often categorized as cool season or warm season annuals. Pansies, for example, are often used as a cool season annual in Salt Lake City as they can survive freezing temperatures of Fall through Spring but will die in the intense heat of the summer. Warm season annuals, such as tomatoes and marigolds, do best in the hot heat of summer and do not need to be hardy, as they do not overwinter in the span of their lifetime. Some perennial plants are treated as annuals, when they are grown outside of their hardiness zone, with the knowledge that they will not survive for more than one growing season. Occasionally, an annual in a microclimate or with particularly hardy genetics may act as a biennial or perennial.
Biennials
Biennial plants have a short, two-year life cycle similar to annuals. Biennials focus on vegetative (non-flowering) growth during their first year, and overwinter if hardy. They use their stored energy to produce flowers and fruit during their second year then die.
Perennials
Perennials have a life cycle that spans multiple years. They can produce flowers and fruit multiple times in their lifespan and are considered hardy if the range of temperatures in an area allow for multiyear longevity. Hardy perennials tend to be very tough and can produce flowers and seeds for many years. Semi-hardy or marginally hardy perennials are those rated for a zone or two hotter than typical conditions in the area and may perish after a particularly cold winter. Short lived perennials tend to die after a few seasons.
Monocarpic vs Polycarpic Plants
Most plants are either monocarpic or polycarpic, which refers to whether a plant dies after flowering. Monocarps only set seed once in their lifetime before dying. They tend to be annuals or biennials; however, some monocarps may be perennials that grow for many years before flowering. Some may even produce offset clones in addition to producing seed. An example of long-lived monocarps are Agave or century plants, so named for living a ‘century’ or many years before sending up an impressive flower spike. Polycarpic plants do not die after flowering, fruiting, and producing seed. They tend to be longer-lived perennials, but must be hardy in the area they are planted in order to survive for multiple seasons.