All perennials need caring for in different ways and we will care for them appropriately. However, general rules apply for caring for perennials and I have outlined these below:
Perennials generally need far less persistent maintenance than annuals. They tend to be hardier plants as their long lifecycle suggests.
Half-hardy and Hardy perennials
Half-hardy perennials, such as fuchias should be brought indoors during the winter months as cold weather can kill such plants. They should be lifted when dormant and stored in moist, temperate conditions. Hardy perennials, on the other hand, do not need to be lifted and taken to an indoor location.
Well established perennials do not need watering but younger, or recently transplanted, specimens will need watering regularly. Most perennials will need watering during times of drought. However, some plants are capable of withstanding droughts such as Dianthus and Geraniums.
An annual top-dressing of bone meal or slow release fertilizer is widely recommended for perennials. Those plants that are grown for their attractive foliage such as hostas thrive on an occasional liquid feed during the growing season.
Weed Killing and Mulches
Mulch can be added to beds, on a yearly basis, containing perennials in order to help the soil retain water and suppress weeds. Weed killers should be applied sparingly and carefully so that we can avoid damaging our chosen perennials.
Top-heavy perennials should be supported with a stake in order to keep them upright, especially if located in a windy area. Staking should be done early in the growing season, as staking later on could lead to plant damage. Stakes should be raised as plants grow. Perennials with numerous stems should be supported with a number of canes.
Dead-heading perennials encourages them to flower again. Dead-heading makes plants put energy into producing more flowers rather than seeds which are usually less attractive. Delphiniums and Rhodendrons are examples of perennials that benefit from dead-heading.
Shoots that are thin and weak can be removed. This allows the plant to focus on its sturdier shoots. This can result in the production of larger flowers. This technique can be used with delphiniums, phlox and Michaelmas daisies.
The number of flowers on perennials that produce numerous side-shoots can be increased by removing or “stopping” the growing tip of each stem. “Stopping” avoids plants becoming too tall and straggly. This technique improves the appearance of plants such as Rudbeckia.
Gardeners tend to prune herbaceous perennials in the autumn so that the appearance of the plants is improved. Tender perennials must be allowed to keep their foliage until April or May of the following year otherwise they could die. Old stems protect the crowns of tender perennials from frost. Penstemons need treating in this way so that they can survive through the winter.
Pruning herbaceous perennials selectively can allow us to rid the plants of dead and decaying material, whilst allowing them to retain pleasant looking dry flowerheads. Sedum spectabile looks aesthetically pleasing if pruned in this way.
Evergreen perennials should not be cut back. However, dead shoots should be removed during the spring and summer months. Cutting away dead foliage rejuvenates them and makes them look tidier.
It is a good idea to divide perennials every two or three years, because otherwise they tend to become too dense and this restricts growth. Some perennials such as Stachys could do with being divided every year, as they are fast-growing. It is best to divide summer-flowering perennials in the spring or autumn. Perennials that flower in spring are best divided in summer when they produce new roots. There is a real art to dividing perennials and different techniques are favoured for dividing different types of plant. Divided perennials should be replanted carefully to allow enough space for each specimen to develop. Dividing perennials gives the horticulturalist the opportunity to clear the area of weeds and add manure or other beneficial products.
Pest and Diseases
Pests such as slugs, snails, aphids and thrips should be kept at bay/targeted by the gardener. An appropriate fungicide is recommended for perennials that are attacked by fungi.