Tuesday 8 October 2013

A passion for rhododendrons.

Guest Post
I am reprinting today a very interesting article written by my friend Peter Williams for the East Yorkshire group of the Hardy Plant Society. I recently wrote about Peter and his beautiful garden In my piece ‘One of Yorkshire’s Finest Gardens’. I hope you enjoy reading Peter’s thoughtful article about a plant about which he has in depth knowledge, loves and grows to perfection. Thank you Pete for this lovely piece and your beautiful photographs.

Rhododendrons – Unloved and dangerous, the tale of one enthusiast
A riverbank in Derbyshire 
I was probably about seven or eight years old when I first became aware of Rhododendrons. It was the Easter holiday and I was with a group of friends in South Wales and we were on one of our regular skirmishes with nature that usually involved building dens, climbing trees and damming small streams.  On this particular day we wandered outside our usual hunter and gather range and came across a small wood packed with Rhododendron ponticum in full flower and I was hooked for life.  I thought that they were the most amazing plants I had ever seen and I just had to take a bunch of the huge flowers home for my mum.  I was expecting a hero’s welcome for returning with such a prize but this was not to be.  Instead, my mum became very flustered and said it was unlucky to bring flowering shrubs into the house and she would only allow them in the windowless garden shed. I could not understand this at all because unlike nowadays, we were encouraged to pick wild flowers and take them home. Only much later did I discover that the wood belonged to a member of the local gentry who owned most of the houses in our village, ours included, and who collected the rent weekly in person. I guess that my mum felt that he might not appreciate seeing a large bunch of his prize Rhododendrons on our living room table.
When I married and we bought our first home, Rhododendrons and Azaleas were right at the top of the list of plants that we wanted for our small garden.  Despite the fact that the soil was not acid, added peat and sequestrene did the trick and they grew reasonably well.  

Our second home had an acid soil and Rhododendrons grew well without having to add peat. Rhododendrons were very much in fashion at this time and expensive to buy. In my day job I was teaching undergraduate students about a technique called meristem propagation that was used to eradicate virus from fruit stocks like raspberries, strawberries, apples and pears. This technique became better known as micropropagation when used to propagate plants that were slow to multiply by traditional techniques.  Rhododendrons were amongst the first hardy ornamental plants to be propagated this way and on a visit to a horticultural trade fair to look for  a new CO2 analyser for our university laboratory, I came across a Canadian nursery selling micro-propagated Rhododendrons.  The range was huge and the small plants, about 3cm high, were very inexpensive (about 50p at today’s prices).  I ordered 500 plantlets in 50 varieties which duly arrived a few weeks later.  I do remember that the getting the plants through customs at Manchester airport and then onward delivery to York  cost far more that getting their health certified in Canada and flying them across the Atlantic!  I grew these plants on and started selling them together with other acid loving species at the early plant fairs at Beningbrough Hall and other National Trust sites.
When we moved to our current home with much more space, I bought a large second-hand poly tunnel and enlarged our range of acid loving plants and started selling plants from home at weekends in spring.  I loved doing this, especially the propagation, but we stopped a number of years ago because of the pressures of academic life and the demands of a growing family.
Rhododendron yakushianum
Most of our customers were knowledgeable fellow enthusiasts but we did have the occasional individual who was unhappy with our plants.  One regular customer came in one weekend and wanted a very special plant for her mother’s ‘significant ‘birthday.   She persuaded me to part with a lovely specimen of R. yakushimanum that I did not really want to sell.  This species is my all time favourite Rhododendron.  It is very compact and has pink bell shaped flowers that fade to white but the most distinctive feature of this native Japanese species is the dense indumentum that coats both surfaces of the leaves. The fine silvery hairs on the upper surface are thought to reflect light to reduce leaf temperature and the very dense, velvety hairs on the underside are thought to reduce water loss.   These features are very important to the species because it grows naturally in very exposed positions on Yakushima, a small mountainous island off the south coast of Japan.
Beautiful indumentum
indumentum on Rhododendron yakushimanum 
Plants of this species were also the favourites of our children who when small, would spend ages gently rubbing off the ‘fluff ‘from the upper surfaces of the leaves to reveal the dark green shiny surface beneath. Unfortunately, the mum whose ‘significant ‘birthday was being celebrated was less enthusiastic and did not like this plant at all.  About a month after the plant left our nursery, it returned in tow with its new and very unhappy owner.   She explained that her daughter had bought it as a special present but she would like to swap it for one that was not diseased.  I was surprised and upset somewhat by this because the plant looked a picture of health.   The unhappy recipient of the plant explained that you only had to look at the plant to see that it was covered in ‘mouldy fungus’ and she was surprised that her daughter,  who she considered to be  a good gardener, had not noticed it herself.  She did not want to offend her daughter so she found out where the plant was purchased and now she wanted a healthy replacement.  She went on to tell me that she had spent hours removing  the ‘mouldy fungus’  from the upper leaf surfaces  with a J-Cloth and Fairy Liquid but within a couple of weeks it had all come back.  I explained to no avail, that the ‘mouldy fungus’ was in fact, the indumentums and it was a major attraction of the plant and many Rhododendron  experts spend more time looking at the indumentums than the flowers. There was no persuading her however, she knew a mouldy plant when she saw one and was having nothing to do with it. This story had a happy end because I was delighted to get my specimen back and she was happy with her choice of a ‘healthy’ replacement without indumentun.
Peacock butterfly on Rhododendron yakushimanum
Despite running down our small nursery more than a decade ago, I have always propagated a few plants each year for use in our own garden and to give to friends and swap with fellow enthusiasts.   I recently gave a close friend who was redesigning her garden, a specimen of Magnolia stellata ‘Waterlily’ . This plant was apparently admired by a work colleague of the friend who subsequently got in contact by e-mail and asked if I had any plants to sell.  I replied that I had a small range of Magnolias and Rhododendrons and a few other shrubs.  Her reply is shown below:
Dear Peter
I was going to express interest in a few rhododendrons, but I watched a TV programme last night about weeds and decided they (rhododendrons) are all rather nasty foreign invaders that won't do much for the general ecology of our garden, so I am having second thoughts at the moment. I will be back in touch soon.
A few days later I received this:
I have now found a website that proves that rhododendrons are a serious threat to the British countryside. It further suggests that once you have them they are impossible to get rid of so I definitely don’t want any thanks very much. 
I am however, still looking for a specimen Monkey puzzle tree so if you come across a good one will you please let me know?
I initially felt offended by this exchange but on a second read I thought it highly amusing - surely she must realise that not all rhododendrons are the same and just what would a Monkey Puzzle do for the general ecology of her garden?  However, it did get me to reflect on R. ponticum which I guessed was the ‘nasty foreign invader’ that my correspondent was referring to.   Now I do appreciate the very serious problems this species causes in many parts of the country and especially so now that it has been recognised as a major host for the very dangerous fungal pathogen Phytophthora ramorum  that threatens many woody species of plant.  However, I was not sure why R.ponticum was so different from all the other species and hybrid Rhododendrons that are impeccably behaved in our gardens. Indeed, in my experience choice plants are more likely to die than run riot even in good growing conditions for Rhododendrons. The answer to these questions has been revealed recently by some fascinating research into the genetics of the invasive and difficult to eradicate wild R. ponticum by James Cullen from the Stanley Smith (UK) Horticultural Trust in Cambridge.  It appears that the troublesome R. ponticum is not a single species but a hybrid swarm (group of interbreeding species) that has arisen by the interbreeding of four species:- R. ponticum from Iberia and R. maximum, R. catawbiens and R. macrophyllum from North America.  The original Iberian R. ponticum is not reliably hardy in the UK but the first two North American species are extremely hardy and have passed on this trait to the new hybrids. The crossing of these four species probably occurred both in nurseries and in gardens in the early nineteenth century and the resulting hybrids escaped into the wild and caused problems we are familiar with today. So just as with many other troublesome weeds (Indian balsam, Giant hogweed, Japanese knotweed)  it is we gardeners who are to blame for the problem.
None invasive ordinary ponticum
James Cullen has proposed that that the invasive ‘ponticums’ be named collectively as Rhododendron × superponticum.
Rhododendrons bought from nurseries do not have the features of the thuggish Rhododendron × superponticum but do have many desirable features provided you have suitable acid soil.  These include vibrant flowers in a wide variety of colours, neat evergreen habit, long life, sizes to suit all gardens or containers and finally transplantability - what other large evergreen shrub can you move in full flower in spring from one bed in your garden to another without it even noticing?  
Yellow and beautifully scented Rhododendron luteum grows wild but does not threaten the environment
The bad press given justifiably to Rhododendron x superponticum has done serious damage to the reputation of Rhododendrons as my e-mail contact showed very clearly above. Further damage comes from the fact that they do require acid substrates and in the potting stage this usually means using peat based composts– so another black mark against this group. These and possibly other factors have meant that Rhododendrons and their allies are now deeply unfashionable – or at least they are  with those gardeners who are followers of fashion and must have the latest Galanthus, Salvia, Heuchera, Hosta or whatever is the ‘To die for’ plant of the day. As we all know, fashions change and I would not be surprised to see them return to favour in the near future – after all what are we going to plant when we get fed up with wild flower meadows and prairie planting!
Rhododendron ponticum in an oak woodland


  1. Where I used to work at Woolley Hall they had a lovely display of rhododendron and azaleas. Also Temple Newsam in Leeds has a lovely display each spring. The colours are beautiful.

    I think the bit about it being unlucky to bring shrubs into the house was maybe a general belief as I was told the same about lilac when I wanted to take a bunch to school.

    1. When I was a kid in Barnsley my parents used to drag me unwillingly round Woolly Hall on country walks. I love the displays of rhododendrons now! And of course Temple Newsam is a classic rhodo garden. The key things to all these wonderful rhododendron landscapes is an acid soil- and preferably high rainfall. Peter would love more rain here where in Seaton Ross it is particularly dry this year

  2. Enjoyed reading about the Rhododendrons and your propagation. The weird stories were fun. I love these evergreens and have some in my garden, I should need a park to have more. The Rhododendron yakushimanum is a special one I have seen in our Arboretum Trompenburg in Rotterdam. Beautiful picture with the butterfly on it.

    1. Yes they do take up a lot of room Janneke. Some of the 'yaks' are more suitable for the smaller garden.


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