Pruning Methodology: Some General Notes
Be sure to use clean cutters and tools whilst you carry out this work. Clean them in a sterilising solution before starting work and clean them regularly as the work progresses. It cannot be emphasised enough that infected wounds and die-back are the products of contaminated tools. Any cuts should be at right-angles to the growth and not slanting.
Most older plants will have a number of tall or spreading branches that need to be eliminated. Remove two or three of these limbs with the goal of spreading the overall volume of pruning over a three-year cycle to make a regularly-shaped framework of branches that will become a sound foundation for future growth. Take care to cut back to just above a side shoot that is heading in the direction that you wish the new growth to take. Avoid leaving a stub when cutting off the limb, cut back close to the side shoot. Stubs tend to die back to a side shoot anyway and the dead wood left behind carries with it the risk of infection at a later date.
If there is not a side-shoot at the location you are intending cutting back to then look carefully for leaf scars and cut immediately above the scars. Rhododendrons produce their leaves in whorls and these are clustered together at the end of the stems produced by each different cycle of growth. These whorls leave scars behind where each leaf has broken off the
branch and the scars are often visible for several years. If the scars cannot be seen then it will be necessary to cut at random and then cut out any stubs that remain after the plant has put out new growth. Rhododendrons usually have two growth cycles each season. Leaf buds are usually formed at the end of the first cycle and either leaf buds or flower buds appear at the branch terminals on completion of the second cycle. In some temperate locations there can be additional growth cycles that take place in-between the two stages referred to above. It may be necessary to cut-back some new growth if some parts of the plant begin to grow more vigorously than others.
Be sure to remove the leaf litter and debris from the general area around the base of the plants and lightly fertilise immediately after they have been pruned. Clearing around the base of the plant will enable the fertilisers to reach the roots and this will help the new growth to get to started. Some authorities suggest a scattering of Osmocote is sufficient, but there is a danger that in hot weather the granules may suddenly release a significant proportion of the feed in a single ‘hit’. I have found that a mixture of the usual recommended strength of Miracid, sequestrene [Maxi-crop or Levingtons, etc ] and a handful of magnesium sulphate to a two-gallon bucket gets the plants off to a good start. This is fed around the base of the plant at the rate of half a bucket per plant; the advantage here is that you know where the mixture is being placed and there are no problems of the rain washing it away. I then generally provide a scattering of bonemeal around the base of the plants as this provides a longer-term feed. Once the fertilisation has been completed the leaf litter can be replaced to form a mulch, but be sure to dispose of any dead branches, paper, or plastic rubbish, etc.
Next year take out two or three more branches using the same process and the same the following year. This approach will enable you to ‘manage’ the shaping of the plant. And, perhaps more importantly for many gardeners, you will continue to enjoy some flowers each Spring throughout the overall process.
Finally, a few words about lichens. These are a fungi/algae association which use the bark as a growth site, not a feeding site. Many old gardens have plants that have become covered in lichen and this tends to be more prevalent on both deciduous and evergreen azaleas. The evergreen azaleas that become badly affected are generally Kurumes, or their hybrids, and some of ‘Wilson’s Fifty’ are particularly noticeable in this regard. I have not noted any particular deciduous cultivars to be especially prone to attack.
Lichen is an indicator of a plant that is under stress and has lost its vigour. It is usually more prevalent in areas with clean air and gardens near the coast tend to be more susceptible. What this means is that lichen is a secondary problem and it is not the primary cause of the lack of vigour, so it is necessary to look much deeper to understand the real problem that needs to be addressed. There are number of possible primary causes of stress and these are all related to poor cultivation. These include, plants being positioned in full sun, damage to the fine roots close to the soil surface and high acidity of the soil. This latter problem tends to be more common in old gardens than first expected, particularly where there has been little, if any, maintenance work over a number of years. Poor maintenance, together with persistent layers of rotting leaves often lead to high soil acidity; but the modern trend towards high levels of mulching, coupled with the over-application of acid-based fertilisers, may lead to the same situation.
There is no practical way of removing lichen. Small areas of lichen that are scattered along the spindly branches of an azalea are not a major concern and, if plant is flowering well, it would be more profitable to address the primary cause of the problem. But in some cases the lichen may extend for long lengths along the branches, or there may be more lichen than bark. In these cases there is no option but to try and re-invigorate the plant by severely cutting-back the affected branches, feeding and mulching.
In Conclusion:
The intent of these notes has been to provide some practical advice, background notes and some alternative ways of approach related to routine pruning of old rhododendrons and azaleas. Back in the early-1950’s I helped to clear and restore the neglected gardens, including a walled garden, of a large old house and since that time I have helped to rejuvenate both mature and damaged plants in a number of old gardens on both sides of the Atlantic. I continue to have an interest in old gardens from an historical perspective and usually visit a few each year. It seems to me that, despite the passing years, pruning has remained a somewhat subjective matter. A number of books have either avoided the subject or the coverage has been somewhat scant and few reasons are given as to why a particular course of action should be taken. For further reading I would recommend The Cultivation of Rhododendrons by Peter A. Cox, Batsford 1993, which also deals with a wide range of other pruning techniques, including shaping for hedging and special effects, creating single stems, cutting out reverted growth, root pruning, propagation work, etc., in a straightforward and practical way.
Whilst it is a myth that rhododendrons and azaleas should not be pruned it is important at the outset to be patient. Be sure to stand back from the plant before you start, think about what you are about to do and what you are setting out to achieve. In this way you are more likely treat an old friend in a way that will lead to an appropriate response from the plant and thus achieve the results you are seeking.