By John Roy, SRS Autumn Review 2014

I recently came across an interesting document online about whether or not rhododendrons “poison” the soil in which they grow. I have always thought that it would not be in a plant’s best interests to poison the environment into which it is fastened, unless it was highly evolved to deal with the toxins of its own creation.

Some portrayers of this theory make bold statements such as: “Rhododendron poisons the soil around it so that other plants cannot grow.” Plantlife.

“It produces toxins, and suppresses other plants by poisoning the soil as well as year round shading.” Greenham & Crookham [West Berks.] Conservation Volunteers.

“Although considered attractive, this belies its true nature which is to shade out native species, leaving an impoverished landscape in its wake. To do this, it has a nasty trick up its sleeve – the roots are actually toxic to other plants! So not only does Rhododendron block out life-giving light, but it poisons the soil as well.” Ulster Wildlife Trust.

“As well as shading large areas to cut out light for other plants to grow, the bush poisons nearby soil with chemicals that kill other species.” Jenny Fyall, news.scotsman.com.

“This [R. ponticum] litter remains even after the plant is eradicated and can form a toxic humus layer, which is reported to retard new growth of other plant species for up to seven years.” Non-Native Species Secretariat.

Dealing with invasive Rhododendron ponticum, the author puts forward his own thoughts, citing lack of light and changes to the natural soil micro-organisms, summarising:

As rhododendron encroaches and the native community becomes impoverished, the biodiversity of the flora and soil biota decline in tandem. When rhododendron has become a monoculture covering many hectares, we can justifiably suppose that very little remains to represent what was once a dynamic, mycorrhiza-supported, species rich community, other than R. ponticum, one or two associated ericoid mycorrhizal fungi and a handful of shade/rhododendron tolerant plants and plucky survivors.

That is a very poor landscape and a disastrous starting point for its recovery.

Recolonisation by native flora of an area cleared of rhododendron is more likely to be inhibited by: (a) soil rendered inhospitable by R. ponticum leaf litter; (b) poor nutrient supply and (c) low availability of nutrients due to local extinction of the soil community that normally facilitates their mobilisation, than by soil ‘poisoning’.

Whether during occupation or after clearance, it would have been better if the rhododendrons had never arrived in the first place.

If one did not consider the alternative implications of catastrophic reductions in biodiversity as discussed above, one might, influenced by rumour, incorrectly conclude that the soil had been poisoned.

The full article was found at: (no longer available)
http://www.slef.org.uk/userfiles/file/slef-pdfs/rhododendron_poisons_the_soil.pdf

There were only 7 replies to the questionnaire.

The following are my questions and a summary of the seven responses

1. Have you cut down on peat use in your own garden? – 7 out of 7 reported that they had cut down on use of peat and particularly its use as a soil improver.

2. Which commercial compost do you use? – Not everyone responded to this question.

· Melcourt Silvagrow, both ericaceous and multipurpose was mentioned by 3 respondents…..? Possibly its support by the RHS was influential.

· Dalefoot was mentioned by 1. This is a compost containing sheep’s wool.

· Arthur Bowers, peat free or reduced peat, Westland, New Horizon and Dobies (ericaceous) all got one mention as did Garden Solutions of Longniddry.

· Homemade compost was mentioned by four, often to be mixed in with commercial brands. Especially with groups of plants other than rhododendrons. One of the 7 relies entirely on homemade compost.

3. How much growing success do you have with peat free composts?

· Multipurpose Melcourt silvagrow was found to be good for general potting of non-rhododendron subjects.

· Dalefoot alpine peat free was reported as being good.

· There was general agreement that the use of peat free composts required a new approach especially as regards watering requirements.

4. Are any plants particularly difficult to grow in peat free compost in your experience?

· One person mentioned Mecanopsis as being particularly tricky.

· Another said that the early stages of rhododendron growth required special care – see general comments. Sterile nature of peat was mentioned as an important factor for seed sowing.

· One respondent said that in his experience, once a good root ball was established on a cutting of a rhododendron, then a general purpose peat free compost was fine.

5. Are there any particularly difficult stages of growth of rhododendrons where compost is very critical?

· 4 out of 7 mentioned seed sowing and pricking out

· 3 out of 7 mentioned cuttings

Additional comments which may be of use or of interest

Dalefoot composts can be ordered from www.dalefootcomposts.co.uk A comment was made that this compost made using bracken and sheep’s wool is not a sustainable product.

One respondent thought that research into a compost with bracken and redwood bark might be useful. That would not be commercially sustainable either.

One respondent thought that pure peat should still be available for a small number of growers with very specialist requirements and where peat may be the least bad alternative.

One respondent thought the composts containing Coir were dreadful and also that Coir should be kept in the countries that produce it where it could be used locally.

One respondent thought that composted wood was very unsuitable because of fungal growth that comes with it.

Three respondents used a mix of peat free ericaceous compost and perlite for sowing rhododendron seeds. In one case the ratio was 40:60

Two respondents used shredded sphagnum moss mixed with perlite for seed sowing.

For potting on, two respondents used peat free ericaceous compost mixed with fine bark and fine grit or perlite or sand. In one case the ratio was 50:40:10

The one respondent who mentioned cuttings used fine, sieved bark mixed with either or both perlite and fine grit.

In summary

1. We did not receive enough responses to be significantly representative of the view of the SRS.

2. Willie Campbell, our President, was aware of these responses when he sent a response to the Scottish Government questionnaire.

There has been no published analysis of the Government consultation as yet but 484 responses are available to read on the website. There may be other responses which will be used in the final analysis although permission was not given to publish them. The majority of the responses published were anonymous.

To find the published responses go to Ending the sale of peat in Scotland – gov.scot (www.gov.scot)

Survey conducted by Marion Kinns,

An SRS Statement by John Hammond and Ian Douglas

Rhododendron ponticum’s capacity to naturalise itself has created much bad press and sometimes
uninformed publicity. It is an invasive plant, spreading relatively slowly by seed and by layering.
In favourable conditions it can over a significant number of years cover wide areas, seriously
disrupting the biodiversity of natural habitats and ecosystems. It is also one of a number of hosts to
Phytophthera ramorum and Phytophthera kernoviae, which are major threats to both the forestry
industry and to gardens. Its capacity to quickly put on fresh growth, having been cut back to the
ground, means it requires grubbing out or chemical treatment for effective eradication.

Legislation in Scotland classifies Rhododendron ponticum as an invasive species that cannot be
offered for sale commercially and which, if possible, should be eradicated. Forestry Commission
Scotland, for instance, in 2011 launched an action plan “to free the national forest estate of
rhododendron”. This is estimated to cost £15m and take to 15 years to achieve, with £1.6m being
allocated for the year 2011-12 (News Release No. 14783). Forestry Commission Scotland
acknowledges that this is an ambitious programme.

Research commissioned by Forestry Commission Scotland in 2008 estimated that in Argyll and
Bute Rhododendron ponticum covered 4,654 ha, of which 85% was in woodland. However, the
report (Edwards C. and Taylor S. “A survey and strategic appraisal of Rhododendron invasion and
control in woodland areas in Argyll and Bute” Roslin 2008) indicated that the area identified as
being covered by Rhododendron ponticum was significantly underestimated. To eradicate
Rhododendron ponticum from the identified areas only was estimated (2008 prices) to cost £9.3m.
The report also highlighted the problem of re-invasion and spread from untreated areas, so that
without comprehensive eradication the areas of Rhododendron ponticum could increase rather than
decline, with cost rising substantially for its eventual clearance, if achieved.

Given that there are substantial areas of Scotland, in addition to those in Argyll and Bute, which
are affected by Rhododendron ponticum it is clear that a high level of public investment will be
required to eradicate this invasive species. In addition, while the Forestry Commission Scotland
aims to free the national forest estate of Rhododendron ponticum this cannot be achieved without
measures being taken to also to eradicate Rhododendron ponticum in areas outwith the parts of the
country covered by its action plan. These other areas are owned by a multiplicity of interested
parties with varying commitment and financial ability to eradicate this invasive species. Kintyre
alone has vast areas covered by Rhododendron ponticum. Unless a comprehensive approach can
be adopted it is likely that the limited amount of funding earmarked for eradication in defined
areas will be wasted.

This failure to identify in the public’s mind the specific cause of the problem, as well as the giving
of very optimistic forecasts for its eradication, will undermine the campaign to eradicate this
invasive species from the Scottish landscape. In addition, misleading information on costs and the
playing down of the risks of re-invasion will ultimately threaten future funding.

The problems of eradicating Rhododendron ponticum are enormous, as its capacity to survive
clearance, re-grow and generate new seed in a relatively short time cannot be under-estimated.
Ambitious targets and a lack of adequate funding will be counter-productive to achieving full
eradication. The Scottish Rhododendron Society has called on the Scottish Government for the
implementation of a national action plan for the permanent removal of the invasive species
Rhododendron ponticum from the whole country. The action plan should be based on a realistic
and open assessment of the scale and nature of the problems involved, engage the support of all
the interested parties and land owners, be properly funded, be effectively managed; and
implemented on the ground without eradicating or adversely affecting, all other Rhododendron
species and cultivars that are not invasive or a threat to natural habitats or ecosystems.

Prior to commencing work on any eradication exercise, it is vitally important to carefully consider
what use is to be made of the land being cleared of Rhododendron ponticum, as the ground will be
devoid of all the nutrients. Rhododendron ponticum is one of very few plants that is able to survive
on barren soil and, for this reason, it is likely that other invasive species will take over the area that
has been cleared unless there is a plan in-situ for rejuvenating the soil and replanting.

For an interesting article by John Hammond on ‘Powdery mildew’ on subsection Cinnabarina, see the SRS yearbook no. 23, 2022.

“There are three potential problems which could affect Leyland Cypress trees – a blight, a canker and root rot. There is also a pest, an aphid.”

Marion Kinns,

By Kenneth Cox, Glendoick

Peter Cox has a long and distinguished career in the rhododendron world.

In the fields of original authorship; development of new plants; innovative breeding, taxonomic studies; plant exploration and preserving of germ plasma through selection of species.

Peter Cox is widely acknowledged both in the UK and abroad, as perhaps the world’s leading expert on rhododendrons.

Over the last 60 years Peter Cox has made an outstanding contribution to his field, brought distinction to British and International horticulture, and enhanced the reputation of the country within the global botanical and horticultural community, through:

Searching for, studying and introducing plants from the wild into cultivation. Through leading or participating in over 25 major plant-hunting expeditions Peter Cox has introduced significant numbers of plants into cultivation for the first time. He is believed by his peers to have identified and studied more species of Rhododendron than anybody living or dead. He has discovered at least 4 new rhododendron species, one of which Rhododendron coxianum from India was named in honour of his father E.H.M. Cox. Several more Peter Cox collected new taxa are awaiting being described.  The thousands of seed numbers collected from four continents have been expertly curated and together with many plants grown from the seed have been distributed to botanic garden collections, private and public gardens in over 20 countries. Peter Cox’s own gardens, on the west and east coasts of Scotland, contain a unique collection of plant species, many from these expeditions, and have attracted the attention of horticulturists from around the world. Peter’s garden at Glendoick has been voted one of Europe’s top 50 gardens (The Independent on Sunday). He has also worked extensively with Indian and Chinese botanists in the field, helping them to identify their native plants.

Development of hybrids for the small garden.  Peter Cox is considered one of the world’s most successful and skilled hybridisers of Rhododendrons. Peter recognised the need for hybrids suitable for small gardens and his efforts over the last 50 years have produced a range of plants suitable for any size of garden. Peter invented the concept of ‘dwarf rhododendrons’ celebrated in his book of that title. Hitherto, rhododendrons had been considered suitable only for large gardens and estates. His first cross was made in 1959 and Peter continues breeding to this day. His hybrids, mostly named after birds, are now to be found in gardens throughout the UK, northern Europe, Japan, Australia and New Zealand and North America. Many of his hybrids such as “Chikor”, “Curlew”, ‘”Ptarmigan” and “Panda” have become commercial standards in the UK and elsewhere, and are stocked in most garden centres. The hybrids have attracted a large number of prestigious plant awards from the Royal Horticultural Society including Award of Garden Merit, First Class Certificate and Award of Merit. His work continues with a focus on producing hybrids with coloured foliage.

Author: Inspiring and Informing. 

Peter Cox’s leading role in horticulture and his highly distinguished reputation for his unmatched knowledge of Rhododendrons (of which there are over 1000 species) is underpinned by his numerous books on the subject. Alone or in conjunction with his father Euan Cox or son Kenneth Cox he has published 13 books, all of which have been well received by critics and the global horticultural community. You would struggle to find a rhododendron fan anywhere in the world without some Peter Cox books on the shelf.

“The Larger Rhododendron Species shows the results of a lifetime’s work among rhododendrons and monumental scholarship”. Popular Gardening

1997 saw the publication of the definitive publication “The Encyclopedia of Rhododendron Species” (Peter Cox and Kenneth Cox, Glendoick Publishing 1997) Taking five years to write, with 400 pages and 1500 photographs illustrating virtually all temperate rhododendron species in cultivation.  This magnificent volume continues to receive accolades from all over the world:

“The Cox & Cox book…is comprehensive, covering all the species. It incorporates the latest research. It has at least one colour photograph of each species and , above all, it is readable. In my opinion it will set the standard for the next 25 years” Joe Harvey, Victoria Rhododendron Society Newsletter, Canada. 

Other books published include:

Modern Rhododendrons, Nelson 1956. Euan H.M. Cox and Peter A. Cox.

Modern Shrubs, Nelson 1958. Euan H.M. Cox and Peter A. Cox.

Modern Trees, Nelson 1961. Euan H.M. Cox and Peter A. Cox.

The Royal Horticultural Society’s Wisley Handbook Rhododendrons,  Peter Cox. A beginners guide. (5 editions-first published 1971.)

Dwarf Rhododendrons, Batsford, 1973, Peter A. Cox

The Larger Rhododendron Species Batsford 1979, 1990.

The Smaller Rhododendrons, Batsford 1985  Peter Cox- cultivation information and species and hybrid descriptions.

Encyclopaedia of Rhododendron Hybrids- 1988. Peter & Kenneth Cox. 1800 hybrids described. A critical guide to choosing from the multitude of hybrids on offer.

Cox’s Guide to Choosing Rhododendrons 1990. Peter & Kenneth Cox. A ‘which’ guide to making a rhododendron collection. An excellent  aid in choosing the best plants for different conditions.

The Cultivation of Rhododendrons P.A. Cox. Batsford  1993 . This well-illustrated book summarises the author’s lifetime’s experience in cultivating rhododendrons.

Seeds of Adventure Antique Collectors Club 2008 (with Sir Peter Hutchison). Lavishly Illustrated account of 20 plant hunting expeditions.

Winner of Garden Media Guild  Inspirational Book of the Year:

The judges commented: ‘Even someone who couldn’t care two hoots about rhododendrons would be gripped by the sheer bloody mindedness of these two as they suffered awkward locals, ticks the size of pennies, food poisoning, sodden tents and numerous travel headaches in their good-humoured quest. The anecdotes are delightful, the photographs of plants, people and views are breath-taking. What an inspiration to us all.’

Providing Horticultural Advice. 

Peter’s advice on rhododendrons is sought throughout the world; he has selflessly given up significant (unpaid) time to advise, counsel and inform amateur and professional horticulturalists and botanist on his subject in Europe, Asia and the USA. He has served on a variety of committees including:

National Trust for Scotland Gardens Advisory Committee

Advisory Board to Arduaine Gardens.

Gardens Advisor to Achamore Gigha, Scotland.

Board of Trustees Dundee Botanic Society.

President Scottish Rhododendron Society.

Awards:

Victoria Medal of Honour, Royal Horticultural Society 1992
Gold Medal, American Rhododendron Society 1993
Royal Caledonian Horticultural Society, Gold medal
Lifetime Achievement Award, Nurseryman & Garden Centre Awards 2000
Honorary Degree University of St Andrews in 2005.
Book Seeds of Adventure written with Sir Peter Hutcheson winner of Garden Media Guild Inspirational Book of the Year 2008.
MBE 2013 (Member of the British Empire), presented at Buckingham Palace

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All over the UK rhododendrons are well budded up for a spectacular show this year, already the Social Media sites are posting pictures of our favourite plants.

Our seed exchange has been well used again this year with over 60 requests and after taking off expenses, we should be adding another £750.00 to our Education and Exploration Fund.

Talking about our E&E fund, the second recipient Colin Jones has been awarded a sum of £1000.00, Colin is Joining a Botanical trip to Yunnan, which is being organised by Seamus O’Brien.

We are holding our Joint Conference with the RSCG in the conference room at the RBGE, which is a venue we have used on many occasions.

“Modern Day Botanical Travels” on Saturday 5th October. We will have talks from Richard Moore on his trip to NE Nepal, John Roy, Jeanie Jones (Primulas) Grant Moir and hopefully Colin Jones about his trip to Yunnan.

We would be arranging garden visits on the Sunday, along with our usual plant auction. (more details later)

However, we still have our AGM and Spring Show at the Gibson Hall at Garelochead on 26/27th April to look forward to, with Plant and Book sales. Teas and Cakes on offer as well. (again, more information from the show committee later)

The updated show schedule can be download from our website.

As we are talking about our website Grant Moir has been busy modernising how we go about attracting members of the public to visit the website at

Scottishrhododendronsociety.org.uk

Please check it out for yourselves, also with links to plant databases.

As members you can visit our members area

Lots of interesting articles, notice board and details on cultivation of rhododendrons.

Other Social media news is that our Facebook page is being visited daily by many and Grant Moir is setting up an Instagram page hoping to reach the younger generation of the public who may eventually become interested in our favourite plants.

As always, your committee is here to help answer questions or queries you may have on plants, gardens to visit, also if you our members may have some suggestions you may like to see the Society becoming involved in, please contact anyone on committee..

With Gardens to visit, our spring tour itinerary is complete, wonderful gardens in the Oban area, with Baravalla and Achamore on Gigha at the end of the week. Hotels at booked in Oban and Stonefield Castle our old favourite down at Tarbert.

We have had someone drop out of the tour, so we have a single room already booked, so if you’re interested in coming along, please contact myself by email. (contact details in members area)

You may like to join the tour just for the day, again contact myself for details.

All for now, snowdrops at my old garden at Gargunnock have been outstanding as have the early rhododendrons, like praecox, Christmas Cheer and sutchuenense blooming away just fine.

Willie Campbell

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Newsletter Feb 2024

I do hope you all have had a good festive season and find that the weather in your part of the world has been kind to you and the garden is all budded up for a spectacular flowering season. I look at my own garden in Doune in Central Scotland, with snowdrops, aconites, early daffodils, crocus and primroses already giving Fiona and I some early season pleasure.

Although the Seed Exchange is now closed, still have plenty seed left and if you would like to get a £10.00 or £5.00 surprise package of rhododendron, trees and shrubs along with companion plant seed. Just Email me. william.campbellwj@btinternet.com

Again, we as a Society must thank all the seed donors, without them no seed exchange. This year so far, we have had over 50 requests and should add around £750.00 to the Education and Exploration Fund.

Other good news is that we have a nomination for the SRS secretary, if anyone else would like to be nominated at our AGM on the 26th April, 2.00 at the Gibson Hall at Garelochead, contact Katrina our current Secretary.

However, we still are looking for new committee members.

1) Someone to help with editorial work on our publications to take over eventually from John Roy. Perhaps taking on editing the Spring and Autumn journals to start with.

2) Someone to come on as Treasurer, again not this very instant but to shadow Colin Whitehead who has been in the job for some 12 plus years.

3) Someone to take on the Tours and Conferences, I have taken over this task, but hope someone will take over completely.

4) General committee, just come on help out with what ever tasks are needing attention, shadow members many of have been on much longer than the three years as per constitution.

As always, we only meet “Face to Face” twice a year, you can now work remote and join meetings on “Zoom” so no excuses, that distance is an object.

Our Spring Tour to Argyll Gardens this year is all booked, Hotel wise but you can still join on a daily basis, please contact myself for details.

Just a reminder, subscriptions were due at the beginning of the year, if you have not rejoined yet, please do so NOW.

I would also like you to join with me and all my committee in wishing one of our Society founder members Peter Cox a very Happy 90 Birthday.

Kenneth has asked if you want to send Birthday Greetings to Peter, just send to cards to

Kenneth who will read your personal messages out to Peter on the 28th of February 2024.

As always, we want you to be involved in the Scottish Rhododendron Society, you can tell John Roy about your Garden, ask Matt Heasman to identify a plant you have, ask advice on plant propagation or John Hammond on the History of our gardens.

Hope to see you all at the Show 17th April at Garelochhead. More details later.

Regards

Willie Campbell

email contact in members area