The strict definition of a perennial is a plant that lives for more than three seasons, but in gardening terms it usually applies to non-woody plants that live two or more years. Many tender or short-lived perennials are often grown as annuals or biennials, for example, foxgloves, hollyhocks and snapdragons.
Many perennials are herbaceous, which means they die down to ground level in winter and re-grow from the base each spring. The disadvantage of this for the gardener is that they can look boring for a considerable part of the year. Some plants, such as poppies, have interesting seed heads but more die down or just collapse and look sad. The way round this seasonal drabness is to plant a mixed border that also includes shrubs, bulbs and annuals to fill in any gaps.
It is worth bearing the following points in mind when choosing perennials.
– The requirements of the plant itself.
– Time and length of flowering season.
– Size and shape of the plant and the flowers.
– The size, shape and color of the surrounding plants.
Perennials are easy to grow and give good results over a long period in return for your efforts. Most are best planted in mid-spring with a layer of mulch to conserve water. Tall perennials will need staking and many will flower repeatedly if deadheaded. Do not be tempted to feed and water them too much when they are young. Left within reason to their own devices they will grow into stronger plants.
Many perennials that flower in late summer or autumn benefit from the ‘Chelsea Chop’ in May. This is named after the Chelsea Flower Show that takes place in London at the same time. Cut back by a third or even more to create a more compact plant that will bear more flowers.
The exact timing obviously depends on the weather but as a rough guide the plants should have reached about two-thirds of their final size. Make sure the plants are strong and healthy, cut back to a bud, and water and mulch afterwards. Echinacea, rudbeckia, helenium, bergamot (Monarda), sunflowers (Helianthus), phlox, Michaelmas daisies (Aster) and heliopsis all benefit from this treatment.
In the late autumn, many need to be cut back to just above ground level and tender species should have their crowns covered with a light layer of dry leaves, straw or bark to protect them from frost. In spring, new growth will appear and any dead parts should be cut away. Every three or four years many perennials benefit from being dug up and divided.. Many perennials flower in the first year they are planted, provide a good display for several months and financially work out as better value than bought annuals because they do not have to be replaced each year.