From Seed to Seed:
Plant Science for K-8 Educators


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Different types of life cycles

    Annual, Biennial, or Perennial?

Annuals. One could argue that the entire life of a plant is geared toward one thing: reproducing. For annual plants, the production of flowers and seeds is the culmination
of their very existence! Soon after annual plants produce mature seeds, they die. In just one growing season, they have exhausted their resources by sprouting, growing foliage and flowers, and finally producing viable seed. Although the mother plant dies, she may have left hundreds, or even thousands, of seeds to carry on her legacy. For annual plants, one generation per year is the norm, so annuals have a life cycle of one growing season. The bean plant mentioned above is an annual.

Other common garden annuals
include zinnia, cosmos, and


Biennials. Biennial plants complete their life cycles over two growing seasons (bi = two). During the first season, these plants grow only foliage, commonly a low-growing rosette of leaves. In the second growing season, they form flowers and produce seeds. After the second season, the mother plant dies. Common biennial plants include foxglove and Canterbury bells. Did you also know that parsley, cabbage, kale, Brussels sprouts, carrot, and celery are also biennials? We usually harvest them during their first season of vegetative growth so we never actually see the flowers.

Perennials. Perennial plants continue to grow and flower for more than two years, and many will live for decades. As with annuals and biennials, perennials produce flowers that, if successfully fertilized, form seeds. The difference is that the mother plant does not die after producing seed. Since we define the life cycle of a plant as the time it takes for a plant to go from seed to seed, a perennial's life cycle can vary widely. For many common perennials, completing a life cycle usually takes from two to perhaps five years. For example, if you plant a coneflower seed, you'll get only foliage the first few years, with flowers and seeds being produced in subsequent years. If the first seed is formed in the third season, then we would say that the plant has a three-year life cycle, from seed to seed.

The word perennial is commonly used to describe long-lived herbaceous plants-those with green, non-woody stems. In temperate regions, most perennials die back to the ground in the winter, then sprout from their underground growth in the spring. Strictly speaking, woody plants are also perennials, since they grow for many years. Commonly, however, a distinction is made between woody and non-woody perennials. The word perennial is reserved for herbaceous, non-woody plants. Woody plants whose aboveground parts persist through the winter are categorized as shrubs, trees, or woody vines.








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