biennial [ bahy-EN-ee-uhl ] noun: a plant that lives for two years, flowering and fruiting the second year
Biennial plants live for two years, usually growing vegetatively the first year (often forming a basal rosette of leaves) and flowering and fruiting or setting seeds the second year, after which they die. Like the annuals, these plants may seem to come back for many years, but it is because they drop seeds that continue the cycle. Gardeners may also harvest the seeds to plant at alternative locations. Some herbs are biennials, flowering and striving to set seeds the second year, producing less of the desired green herb for culinary use. Basil is a biennial or short-lived perennial in its native tropical habitat, but is grown as an annual in the Mid-Atlantic Region because it becomes increasingly sensitive to temperatures as they descend below 50 degrees.
Non-natives Verbascum thapsus (woolly mullein) and Alcea rosea (hollyhock) and native Rudbeckia hirta (black-eyed Susan) are all biennials that reseed readily, becoming invasive in some areas. The latter two are also considered short-lived perennials. Additionally, black-eyed Susan is often referred to as an annual because it can establish so easily, blooming in the first season from seed sown early spring. How black-eyed Susan acts in the garden–as an annual, biennial, or short-lived perennial–depends on its environment. It is highly adaptable, adjusting its life cycle to yearly weather conditions, soil conditions, and the amount of daylight that it receives.
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