Annual flowers bloom in the year they are started from seed/planted, with many varieties directly garden sown. Once annuals start to flower, they generally do so for an extended period, only stopping when killed by the onset of cold weather in the fall.
Biennials are planted one year, grow through the year, overwinter as a plant, then grow on and flower during year two. When flowering is finished, the plants will produce seed before dying. It is advisable to initially plant biennials for two years in a row to enjoy continued flowering year-to-year.
Perennials are hardy enough to survive our winters conditions and come back from the same root every year. Most perennials started from seed (except those started early indoors) will not flower until their second season of growth. Unlike annuals which flower summer-long, perennials generally have a 2- 4 week flowering season, although some perennial species do flower for a much longer period.