Perennials, Biennials and Annuals

Perennials and Biennials

Cottage style plantings often have a variety of hardy perennials and shrubs as their main interest. These may be augmented by the sowing or planting with annuals and tender perennials to give year long colour. 

There can be some confusion as to what is a perennial, a biennial or an annual. So what is the difference between perennials, biennials and annuals?

Perennials

Perennials are plants that return year after year. Some are evergreen and some die back at the end of the season.  Herbaceous perennials flower during the summer, set seed and then die back over winter to regrow again the following spring. There are some perennials that will flower earlier however the lifecycle is the same. For example spring bulbs such as narcissi.

Biennials 

These plants are sown one year and flower in the following year to set seed. Examples are wallflowers and carrots.

Annuals

Annuals complete their life cycle germinating, flowering, seeding and dying in the same year.

In the UK there can be confusion when we treat some plants differently to their natural cycle.

Tender perennials are often grown as annuals as they are killed by the frost. In milder or more sheltered areas they may survive the winter with protection but a hard winter can easily kill them off unless they are stored in a frost free place. Some are so tender they need heat to survive in our UK climate.

Some hardy annuals are treated as biennials and can be sown in late summer or early autumn and will then be more likely to flower earlier in the following year; for example, sweet peas, some poppies, nemophila baby blue eyes, canterbury bells (annual) and honesty. 

Some perennials are treated as annuals to give a better display of flowers as flowering tends to be poorer in subsequent years e.g. hollyhocks, delphiniums. Or they may be affected by adverse weather conditions such as with waterlogged soils and so would be more likely to die off; for example, salvias.

There are many types of herbaceous perennials - those that are used in established borders. Herbaceous means their foliage dies back after flowering but they remain in the ground for the following year. Bulbs, rhizomes, shrubs and trees are also perennial and like herbaceous perennials they can be deciduous or evergreen, short lived or longer lived.

Perennials need to be the right plant in the right place. Moisture, site and sun requirements vary depending on the plant and the variety. Also how hardy they are and what temperatures they need. For example, perennial salvias do not like sitting in continually wet soil, especially overwinter and they will often die off after a few years in such conditions.

When should I sow perennials and biennials?

Check the seed requirements. Sometimes the seed needs a period of cold weather for the seed to prepare for germination in the spring; this is known as stratification. Some seeds need light to germinate, others need dark and some don’t mind and will grow whatever.

If you are thinking what to sow now - if you have any time or are wanting to prepare for next season then the following may be seeds to consider.

Perennials might include hollyhocks, aquilegia, campanula, penstemon ,delphinium and ornamental grasses. Biennials could be foxgloves, sweet william and forget me not. Some hardy annuals are poppies cornflowers, larkspur then, of course across all genres, wildflowers of all kinds.