Annuals and Biennials
An annual is a plant that completes its life cycle from seed to seed within one season – that is, it is sown as a seed, flowers, sets seed and dies within a single year. Lathyrus odoratus (sweet pea) is an annual. Some plants, such as some types of lobelia and Rudbeckia are really perennials that are capable of lasting for many years, but perform better if they are treated as annuals, or cannot survive the British winter.
A biennial is a plant that requires two seasons in which to complete its life cycle – it establishes itself in the first year and then flowers and sets seed in the second year. A well-known example of a biennial is foxglove (Digitalis spp.)
Biennials really come into their own in the early part of the season because they have a head-start over any annual, no matter how early it is sown. Two of the best biennials are Erysimum cheri (wallflower) and Dianthus barbatus (sweet william).
The annuals that give the best flowers in the early part of the year are those that are tough enough to have been sown the previous autumn, and although they won’t have had as long to grow as the biennials, they will also be approaching flowering by early spring. The following are popular choices: Centaurea cyanus (cornflower – left), Clarkia amonea (satin flower), Consolida ajacis, Echium vulgare (viper’s bugloss), Gypsophilia elegans, and Lobularia maritima.
A half-hardy plant is one that can be grown outdoors in summer but should not be planted or sown outside until all danger of frost has passed because it will not withstand temperatures lower than 0oC (32oF). Tagetes spp. (French and African marigolds) are half-hardy.