Perennial? Biennial? Annual? What does it all mean?
Plant type categories may seem a bit confusing, but in fact they simply group plants by their life cycle. Here’s a definition guide to the three types of plants:
The word perennial means plants which flower reliably every year, usually growing in size each time. The stems die back over winter but the roots don’t, so the plant will regenerate the following year.
Most plants in this category fall under the title ‘herbaceous perennials’, with the exception of trees and shrubs which don’t die back to ground level over winter. These are sometimes referred to as ‘woody perennials’.
There is a huge range of perennial plants, and they can be used for a wide variety of planting schemes. Perennials work especially well in borders: classic plants include lilies, salvia, cranesbill, peonies, hydrangea, campanula, delphiniums, alchemilla and kniphofia (red hot poker) to name just a few.
Biennials are plants which have a two-year life cycle. During the first year, they grow only the roots, stems and leaves, and then in the second year they come into flower, produce seeds and die.
Pansies, foxgloves, wallflower, hollyhocks, evening primrose and Sweet William are all biennial plants. Some biennial plants are grown as annuals, such as parsley and celery.
To ensure continuous yearly flowering of biennials, plant a new batch during the year that the first ones come into flower. Many biennials are also self-seeders, meaning they spread seed around the parent plant.
Annual plants are germinated, come into flower, set seed and die during one season or year. Hardy annual seeds are sown in the site where they will flower – poppy, cornflower and nigella are all hardy annual flowers.
Half-hardy annuals are sown in pots and kept sheltered in a greenhouse. These are then planted out later in the year when the risk of frost has passed. Half-hardy annuals include cosmos, lobelia and nasturtiums.
Most prolific flowering summer bedding plants are annuals sown from seed: marigold, petunia, pelargonium and impatiens (Busy Lizzies).
Grow annual plants year after year by harvesting the seeds.