By taking a few simple pruning measures, some rhododendrons can be enhanced in shape
and habit, resulting in a profusion of vibrant flowers in years to come
Shaping the plant
Most rhododendrons need little pruning other than the removal of dead wood, but occasionally it may be necessary to cut plants back where they are growing over paths or too closely. Try restricting such plants by following long growth back into the shrub and pruning out at a sideshoot, rather than cutting back all shoots. This produces a natural-looking shrub and ensures flowering the following season.
How to prune
Many rhododendrons respond to hard pruning, but response is better from deciduous azaleas and rough-barked selections such as R. ponticum than smooth-barked kinds. Undertake hard pruning in early spring and less-severe pruning immediately after flowering. Cut back just above a dormant growth bud - often difficult to locate on older wood. If no bud is visible, cut back leaving about 30cm (12in) of stem.
With many of the large-leaved species and smooth-barked rhododendrons such as R. thomsonii, R. taliense and R. barbatum and their hybrids, it is advisable not to prune hard, as they are very shy breaking into new growth from smooth hard stems. If pruning is necessary, it is generally better to cut back a portion at a time, always going back to a whorl of leaves or above a bud scar.
Aftercare
After pruning, feed, mulch and keep well watered to encourage new growth. On all variegated rhododendrons prune out green reverted growth. Most rhododendrons are now propagated from cuttings but at one time were often grafted onto R. ponticum rootstocks. If grafted shrubs are cut back they may produce suckers. Remove as soon as possible by digging down to the root and pulling the sucker away.
Tony Dickerson