Perennials

Perennial plants provide flowers in our gardens year after year. They are planted together to create herbaceous and mixed borders, which peak in interest in summer and early autumn. However, they can provide colour through much of the year (except the depths of winter) with careful planning and planting.

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Quick facts

Group Perennials
Planting time October and April is best
Height and spread From less than 20cm (8in) to more than 2.4m (8ft) height and spread
Aspect sun, part shade or shade
Hardiness H7 (very hardy) to H1a (heated greenhouse – tropical)  
Difficulty Easy to Difficult

What are perennials?

The term ‘perennials’ is used loosely by gardeners to indicate those plants which grow in beds and  borders, which are not trees, shrubs or bulbs. They are the ‘summer colour’, the ‘border flowers’ and make up a ‘flower garden’.
The two terms commonly used by gardeners are:

  • Perennials This is used for all non-woody perennial plants, including herbaceous perennials. It includes those which are evergreen or semi-evergreen such as Bergenia (elephant’s ears), epimedium, hellebore, Stipa gigantea (an ornamental grass).
  • Herbaceous perennials differ in that all the stems die back in late autumn and early winter. The roots then survive below ground during winter, shooting again in spring. Well known examples include delphinium, geranium, miscanthus (an ornamental grass) and sedum.

To be more botanically precise, the following applies:

  • Perennials plants usually live for many years (those described as ‘short-lived’ perennials may only live for a few years) and vary substantially in shape, size and habit 
  • The foliage may be evergreen or die back in winter
  • It should be noted that the term perennials is often used by gardeners to exclude woody plants (trees, shrubs and sub-shrubs). However, botanically, ‘perennial’ just means plants that live for many years, so can be applied to woody plants too

Cultivation

Perennials are widely used in the garden. However, the two main uses are in:

  • Mixed borders: here herbaceous perennials are used along with bulbs, annuals, biennials, ornamental grasses, trees and shrubs to create a display. This is the most common use in gardens – and, in reality, is a general garden bed or border
  • Herbaceous borders: are displays of herbaceous perennials, grouped together for maximum summer impact. These are now rare as smaller gardens need borders to have interest throughout the year

Planting: Most perennials are usually reliable and easy to plant successfully, but some from warmer climates suffer in winter and need the shelter of a wall or greenhouse and well-drained conditions.

Staking: many tall perennials will need staking to hold the flowers upright and prevent flopping.

Pruning

Perennials need little pruning. However, there are two instances where it is needed:

  • Cutting back: herbaceous plants die back in autumn and the dead stems are cut off at ground level either in autumn or late winter
  • Chelsea chop: Some plants which are liable to flop over are reduced in height at the end of May to produce stockier plants

Propagation

Many perennials can be raised from cuttings; softwood and semi-ripe. Others can be raised from seed. Perennials are also usually divided.

Cultivar Selection

With an enormous range of perennials offered by garden centres and nurseries it is possible to find ones to suit a wide range of sites. Selecting the right plant for the right place and soil conditions and buying a good quality plant is important if the perennial is to thrive.

There are thousands of perennials to choose from and some of the best can be seen on the RHS Find a Plant.

See the links below for help with choosing suitable perennials for your garden as well as our page on choosing plants for perennial borders:

Soil types

Problem areas

Plant groups

Problems

Perennials are usually very robust garden plants, but sometimes will start to decline for no apparent reason. This often starts with browning leaves but may indicate an underlying disease such as phytophthora or pythium root rot.

Young foliage and susceptible plants can be affected by slugs and snails, rabbits and voles.

Yellow leaves (chlorosis) indicate a nutrient deficiency.

It is important to stake taller or unstable perennials to prevent plants flopping and the flower spikes falling over.

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