Deadheading of Rhododendrons
Head Gardener, Isel Park, Nelson, New Zealand
Reprinted with permission from New Zealand Rhododendron Association Bulletin.
We expect much of our Rhododendrons. They must flower prolifically every year, grow vigorously and always look healthy. They must tolerate scorching sun and wind, or too much shade. They must put up with heavy soil or light stony waste. In all they must be perfect garden plants.
The amazing thing is that they will do just this, accommodating as they are, but obviously it is not without a little help from their friends, you and I, the rhododendron enthusiast. For plants to perform well in our gardens there are some things we must do that would not normally occur in the wild. One of these is deadheading.
Rhododendrons growing in the natural state tend to flower well only every second year, the intervening season being given over to the production of enormous quantities of seed. This of course is necessary to ensure the survival of the species and those who have seen the regeneration of rhododendrons on burnt over or cleared ground can testify to the prodigious amount of viable seed produced. However, we are not particularly interested in seed from our plants, rather a good annual display of bloom. This is where deadheading can assist. Removal of the fading flowers allows the plants energy to be channeled into bud production for the coming season.
The ideal time to deadhead is as the flowers wilt and fall and with most rhododendrons this is a very simple operation. If the base of the flower stalk is gripped between thumb and forefinger and bent sharply to one side, it will snap off cleanly. Care should be taken that new growths which will be developing in most cases from around the base of the flower stalk are not broken off. But even the loss of the odd shoot or two will be far outweighed by the benefit to the plant as a whole.
If you have only a few rhododendrons, deadheading will be no problem, but obviously the larger the collection and the larger the plants more work is involved. However, if each plant is done as soon as the flowers fade the job is spread out and not such a chore. Leaving the deadheading until later may negate the purpose of it somewhat as energy will already be going into seed production and flower bud development suppressed.
I have found that R. griersonianum and its many offspring seem to suffer more than most if not deadheaded. Flowering becomes sporadic and bushes become straggly and untidy looking. The 'Scarlet King' group certainly come into this category. Some rhododendrons are difficult if not impossible to deadhead. These are generally the smaller, dwarf hybrids and alpine species that produce myriads of small flowers with no definite stalk. Once again, if you have only a few plants and plenty of patience, pinch these off with your finger nails. R. carolinianum is a plant that does not do at all well unless the numerous small trusses are removed. Otherwise do not worry about these small plants, it is fortunate that they generally reward us with plenty of flowers anyway. If you wish to save some seed then it is a simple matter to leave a pod or two on the plant.
You will find that rhododendrons with R. griffithianum blood (or sap) in them, for example, the Loderi group, have incredibly sticky flower shoots, particularly the calyx, so that deadheading is a rather stuckup affair. Many times have I walked away from this job with sticky calyxs firmly attached to the hairs of legs and arms. Nevertheless the benefits far outweigh any inconveniences such as the loss of a few hairs.
Over the last three years we have endeavored to keep right up with the deadheading of our nearly nine hundred rhododendrons, quite an undertaking, but the results have been very gratifying. The amount of flower produced and the general vigor of the plants has increased considerably, with some plants quite dramatically. This has been especially true of the large leaved species, although deadheading becomes a little daunting over the fifteen foot mark.
So deadhead your rhododendrons if you possibly can, you will find the time and effort well worth while.
Note. The curator of the Pukeiti Rhododendron trust Mr. Graham Smith informed the Editor that deadheading is also carried out annually at Pukeiti. This task takes up to twenty people working at any one time and is spread over a period of four months.