By definition, a perennial is a flowering plant that lives for three or more years.
Perennials are herbaceous, which means that they have fleshy rather than woody stems like shrubs. The top growth dies down in the winter, but the roots persist and send up new growth each spring.
There are many different types of perennials but all please us by coming up, unprompted by humans, in response to weather changes once winter is over.
Biennials only come back once, whereas perennials happily situated are more predictable about returning. Additionally, with light, water, and air circulation most perennials increase in width year after year.
Generally they only bloom for about 3-4 weeks at a time, so a variety of perennials is needed in a garden to ensure that there is a succession of bloom from spring through fall. Annuals, biennials, and bulbs are useful to plant with a variety of different perennials to ensure continuity of color in a garden bed.
Gertrude Jekyll, the famous English expert on designing perennials borders, said, “Mix and match sizes, shapes, and colors so there is a pleasing combination across the entire gardening season.” Most perennial gardeners still adhere to her sage advice today.