Cultivation of Hardy Perennial Plants
1. Growing Conditions  >
Selecting Plants  >
3. Planting  >
Weeding:- Weeds are often not much of a problem in established beds, as the plants dominate the weeds. Mulches and groundcover plants will further subdue weeds. Pulling up weeds avoids damaging the roots of the plants, while hoeing is faster. If there is a severe problem with perennials weeds, digging to remove all the roots or spraying with a deep acting weedk-iller like glyphosphate may be necessary. In wild or semi-wild gardens the weeds are part of the display, and any too dominant plants can be cut back or partly removed to allow the weaker plants to survive.
Watering:- Some plants (eg lavender) can survive without being watered at all, once they are established, while others need watering in dry periods to survive (eg gunnera). A good general approach would be to give them a good soaking during long hot dry periods in summer, and if the plants start wilting. Plants that wilt in the day will often recover at night, and the evening is the best time to water. Mulches will reduce water loss significantly.
Feeding:- Generally speaking most perennials do not really need supplementary feed, although it will not do them any harm. Digging manure or compost into the soil when preparing the bed will improve the soil fertility and structure. An organic mulch will have the same effect. Liquid, powdered, granular or slow (controlled) release organic or chemical fertilisers can all be used as top-dressings, especially for those plants that respond to feeding (eg delphiniums). Most pot-grown plants have slow release fertiliser granules in the compost anyway, which will give the plant a good start.
Mulching:-A mulch will smother weeds and reduce the need for watering, and may also add nutrients and organic matter to the soil. Many plants will grow better with a mulch than without. Gravel (eg 10mm or 20mm shingle) is a good mulch, especially in a dry garden. Woven plastic sheeting is probably the longest lasting mulch. Compost, manure or rotted straw will break down to add nutrients and organic matter to the soil.
Staking:- The stems of some tall plants with large flowers will break in wet windy weather. Staking is most effective if done early, before the plants fall over. There are compact varieties, which do not require staking, of many of these plants.
Cutting Back:- Many plants which flower in early to mid summer can be encouraged to produce a second flush of blooms later in the year by cutting off the first set of flower heads before they can set seeds. Trimming dead flower heads also tidies up the flower border. Late summer flowering plants are unlikely to bloom again. The seed heads can look good in winter, provide food for birds and produce new seedling plants. Some plants, such as comfrey, spread so vigorously that you may want to cut them back hard after flowering, if you want to stop them taking over the whole border.
Pests:- Generally speaking pests are not a serious problem. So the best approach is usually to keep an eye on the plants, and then deal with any major infestations as and when they occur. Natural predators, such as blue tits and great tits, make a good job of keeping insect pests down in many gardens. Growing susceptible plants, for example hostas in our damp shady garden, in containers can make pest control easier. Chemical controls are often effective. There are a number of sprays and pellets which are not harmful to wildlife available now (eg ferric sulphate or aluminium based slug pellets and white oil or permethryn insecticides). If a particular plant is badly affected by pests in your garden, then there may be a suitable substitute plant which will do the same job and is not affected by the pests.
Diseases:- As for pests, the best general approach is to monitor the situation, and try to recognize and deal with any problems at an early stage. Diseases often tend to be related to the plant being under stress from poor cultivation or an attack by pests. For example, not letting asters, monardas and many other similar plants dry out in summer will minimize mildew attacks. Moving a plant to a part of the garden with different growing can result in greater vigour and less disease. Spraying can be effective against mildew and other diseases.
- Division:- Many, but not all, perennials can be divided to make additional plants. The method of splitting depends on the type of plant, and to some extent the time of year. For example, an ajuga will produce more or less separate plants from runners, and these can be transplanted without disturbing the original plant. Whereas an astilbe will form a woody mass of a rootstock, which can be dug up when dormant and sliced up with a knife to make a number of pieces, each with a bud and some roots. It is largely a question of examining the plants and learning by experience.
Division is generally best carried out in Spring, as the plants are beginning to start new growth, but many plants can also be divided in Autumn. The new pieces can be planted straight out in the ground, or grown on in pots for planting out later. Smaller offsets and less vigorous plants are more likely to need growing on it pots before planting out.
With age, the shoots of some perennials, for example aster novi-belgii and leucanthemum, become weak and overcrowded in the clump. Digging up the whole plant and replanting the more vigorous shoots from the outside of the clump will rejuvenate these plants.
- Seed:- Most plants which are a species, as well as many named varieties, will produce seed which can be collected and sown. Left to themselves many will self-seed. Generally speaking seeds germinate best around 20oC in moist and light conditions, but away from direct sunlight. There are many exceptions though, particularly those seeds which need special conditions (eg warmth, then frost, then warmth) to germinate. The seedlings can be grown on in pots and then planted out when large enough.
- Stem Cuttings:- Many perennials can be grown from stem cuttings. The cuttings can be taken either from the new basal shoots that appear from the roots in Spring, or from the stems in summer. The cuttings generally root best under similar conditions to germinating seeds.
- Root Cuttings:- Root cuttings about 2-4 inches long should be taken from roots as thick as possible, up to a maximum of around the diameter of a pencil. Then place them either vertically, preferably the right way up, or horizontally in and lightly covered in compost, in a cold frame, ideally in November, December or January. Once they have produced shoots and small roots, usually around mid-summer, they can be transferred to pots and grown on before planting out when large enough. Plants which can be propagated in this way include phlox, anemone and acanthus.
Back to Top