This is what the ASmerican Rhododendrom Society says:
'It is desirable, with the large flowered rhododendrons, to remove the withered flower clusters after the blooming season. This is fairly easily done as the central axis of the cluster, usually called a truss, will break free from the plant with a quick snap of the thumb pushing on the side, or can be cut off with a hand pruner. With the smaller flowered rhododendrons and azaleas, dead-heading is labor intensive and and generally is not required.
Dead-heading is usually done to make the bush look more attractive, to reduce the prevalence of fungus and to prevent a heavy set of seed. If it is not possible to remove the old flowers, it is usually not too detrimental, but flowering the next year may be reduced.'
This should be done when the petals fall, depending on the variety of rhodo you have. Now is surely better than not at all.
I put some in last autumn & didn't know to deadhead, so thanks. They do look rather untidy.
Watering wise definitely worth thinking about. I noticed all my new azaleas & rhodys wilted a while ago. I guess they don't have deep roots yet & there is sadly an enormous tree in the neighbours garden right near the boundary, so it probably takes most of the water from that border.
So in spite of the rain, watch out for watering still! Same with camellias, I always water mine if needed now as I think that also helps them flower next year.
It would be interesting to take the dead flowers off just half the shrub and see whether it made any difference.
The American Rhododendron Society (quoted above) seem to suggest that there are other reasons to do it. I can understand the tidiness argument in certain situations and as a personal preference, but plant health is a diiferent issue. I wonder if the gardeners at Inverewe Gardens and other arboretums with 10 metre high species spend a lot of time precariously swinging about taking off every last seed head.
Obviously not, but then things are a bit different in the average private garden with limited space and the need to maximise the iumber of flowers and make every corner of the garden count.
Which brings us back to whether the reasons for pruning (apart from appearance) suggested by the Americans have any validity.
Here's Millais Nurseries' advice (rhodo specialists) -
'Dead heading is the process of snapping off the spent flower truss after flowering. It really does make a difference, and gives the plant that well groomed look for the rest of the season. However in reality, it is not always possible due to the size of the plants or the size of the garden. Therefore prioritize the operation, and concentrate on your younger plants, and those which seem weak or sick.
If you do not deadhead, then the plant will waste loads of energy making big fat seedpods, and this will inhibit growth and flowering the following season.
Simply snap the flower truss off at the base, above the whorl of leaves, using your thumb and forefinger. Be careful not to break off the new growth coming through underneath. You will soon be an expert and it will certainly pay off next season!'