Report on replies to the Questionnaire on use of peat sent to members in February 2023

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,

A Response to Comments in the Press on Rhododendron ponticum.

An SRS Statement by John Hammond and Ian Douglas

Rhododendron ponticum is found chiefly in the wild in the Caucasus and N. Turkey, and in isolated pockets in Portugal and S. Spain. It was one of the first rhododendrons to be introduced into Britain, in the mid-18th century, with its ubiquitous purple to pink flower. Subsequently in the 19th century Rhododendron ponticum was planted not only for ornamental purposes but also to provide shelter, game cover and has been used as a hardy under-stock for grafting many hybrid rhododendrons.

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.

“Rhododendron ponticum is one species in a genus that contains over 1000 species of
rhododendrons and countless hybrids that have brought pleasure to professional and amateur
horticulturalists and garden lovers alike. None of the other species or hybrids have shown the
ability of Rhododendron ponticum to spread invasively. The rhetoric of press releases fails to
isolate Rhododendron ponticum as being the specific problem:”

“FCS aims to be rhododendron free (in 15 years)!”
“Everyone needs to do their bit and report any rhododendron that they see…”

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.

General Plant Health Advice

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

Sirococcus tsugae

This was originally seen in the United States but first reported in the UK, including Scotland, in 2014 and 2015. It affects the genera Cedrus and Tsuga; cedars and hemlocks. Symptoms are severe shoot blight and defoliation. Dead needles have a characteristically pink colour and later go brown. There can be cankers and bleeding of resin from the bark. Spread is via rain splash and high winds. There is no effective control other than biosecurity and plant hygiene.

Marion Kinns, 2022

Stink Bug

Of less concern to us is a new Stink Bug originating from China and Japan. This has been highlighted by the RHS. The brown marmorated stink bug, Halyomorpha halys spread to the USA in the 1990s and is now found in various European countries. So far only adults have been discovered in the UK and no breeding populations.

They differ from native stink bugs with pale bands on the antennae, a row of pale dots on the body and a rectangular head. They appear to overwinter in houses.

The main threat is to orchards where a small number can cause great damage. Gardeners are asked to watch for them. If you find them, capture them and report suspects to bmsb@niab.com or via the RHS gardening advice service rhs.org.uk/myadvice

Marion Kinns, 04/02/22

Phytophthera pluvialis

Presently known to affect a variety of trees including western hemlock, tanoak, Douglas fir and various pines. It was first reported from Oregon, USA in2013 on tanoak ( Lithocarpus densiflorus) and Douglas fir and has been shown to be the causative pathogen in ‘red needle cast’ in radiata pine in NZ. It also causes shoot die back and lesions on stems, branches and roots.

It wasn’t seen in the U.K. until September 2021 in a Cornish woodland where it was found to be affecting mature western hemlock and Douglas fir. Further outbreaks have been found in Cornwall, Devon, Cumbria and near Loch Carron in Scotland. Wales reported their first outbreak in Dec2021.

Many members in our society will grow conifers so this fairly recent pathogen must be of concern. We have also seen how other Phytophtheras ( ramorum and kernoviae) affect a wide range of hosts including the genus Rhododendron.

Growers are asked to be alert to this disease and report any concerns via The TreeAlert online portal. Phytophthera pluvialis currently meets the criteria to be classified as a GB Quarantine pest for regulatory purposes.

Marion Kinns, 2022

UPDATE : 2024

“Early investigations at various gardens have been encouraging in that there has been no sign of this particular fungal pathogen causing a problem in rhododendrons.“

Marion Kinns,

Phytophthera austrocedri

This soil and water born fungus affects our native juniper which is already rare so there is some real cause for concern. It affects and damages roots leading to death. Discolouration of the foliage is seen which is either a uniform bronze following root damage or patchy from lesions on stems or branches. Tongue or flame shaped lesions up to 50cm can be seen under the bark and sometimes resin pockets. There is no natural resistance but plants on drier sites may survive.

Marion Kinns 04/02/22

Plant Health Questions & Answers

“Your President, Willie Campbell asked me, in my capacity as Plant Health watchdog for the SRS, to investigate problems he had observed in his locality of Doune and in Central Scotland generally.

Willie’s observations were that ‘Horse Chestnuts were dying and cypress hedges, especially the golden ones were dying off’. The following was the result of my investigations.”

Marion Kinns,

Horse Chestnut Bleeding Canker

This is caused by a bacterium, Pseudomonas syringae, pathovar aesculi. From a tree survey conducted across the UK in 2007, it was discovered that half of all trees surveyed showed some symptoms. This disease was first seen in the UK in 1970 and is thought to have arrived from India. Trees of all ages can be affected. Some infections can last for years with little impact on the crown but in other cases the spread can be rapid causing crown thinning, die back and sometimes death of part or of the whole tree. Symptoms noted are cracks in the bark and oozing of a reddish brown sticky liquid. These dry in the winter to leave a rusty brown or black deposit. Under the bark the wood is found to be discoloured with brown or purple discolouration as opposed to the usual white/pinkish colour. In older plants dead bark may fall away to expose the wood beneath.

All plants now sold in the UK must be produced in the UK. If this bleeding canker is observed it should be reported to plant health authorities via Tree Alert at forestresearch.go.uk

(this information was found on the Woodland Trust website www.woodlandtust.org.uk)

Marion Kinns,

Horse Chestnut leaf blotch fungus

This is caused by the fungus Phyllostica paviae. Irregular brown blotches of dead tissue are seen on the leaves. Sometimes these have a yellow edge and sometimes the leaf shrivels totally. This is more prevalent in the south and west of the U.K. and was introduced to this country from N. America in the twentieth century.

Horse chestnut leaves are also sometimes seen to gradually turn brown and shrivel all round the edges, looking like severe water stress. This is not leaf blotch and the cause of this condition is not yet known. (this information was found on the RHS website www.rhs.org.uk)

Marion Kinns,

Horse Chestnut leaf mining moth.

This was first found in the UK in 2002 and the moth concerned is Cameraria ohridella. White or brown batches are seen on the foliage from June to September. Caterpillars or circular pupal cocoons can be seen in the mined area of the leaf if it is held to the light. By September the tree may look as if it is dying but it will survive. Leaves may be dropped early and conkers may be smaller. (this information was found on the RHS website www.rhs.org.uk)

Marion Kinns,

“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,

Cypress needle blight

This is caused by another fungus, Passalora sequoia. Symptoms are needles browning and dropping, usually beginning on the lower branches. Spores are spread by rain, winds and tools. To avoid this disease, trees for hedging should be placed far enough apart to allow sun and air to pass through the branches. Infected branches should be pruned out and the loppers used should be sterilised. Do not chip or compost infected branches.

Marion Kinns,

Canker in Cyprus trees

This is another fungal disease and is caused by either Seiridium unicorne or by Botryosphaeria . In the former, the cankers rarely girdle the stem and in the latter they can girdle the stem. The cankers are dry lesions and are often sunken. Surrounding bark can show dark brown or purple discolouration and water flow can be restricted by these cankers. Branches can be seen to die back and there can be oozing of sap. It is found that canker tends to occur only on stressed plants. Fungicides are not effective. Recommendations are to plant trees a minimum of 12-15ft apart and avoid over fertilising. Infected branches should be pruned out, sterilising the pruners. A programme of regular irrigations should be followed and the trees should be mulched to the drip line.

Marion Kinns,

Root rot

Species of Phytophthera fungus are responsible for this condition. Roots die off and foliage goes yellowish, purple or tan. The whole of the tree is affected. There is no chemical treatment. It is often caused by planting where the drainage is poor and young plants are most often affected.

(information for the above three diseases was found at www.gardeningknowhow.com and the RHS website www.rhs.org.uk

Marion Kinns,

Cypress aphid (Cinara cupressiora)

Damage develops in late spring and summer and is most often found initially at the base of a hedge. The pest is a large greyish greenfly. Brown patches often develop after the aphids have gone. It is, however, possible to see cast aphid skins and sooty mould which grows on the honeydew excreted by the aphids. Damaged hedges can recover but this can be a slow process. The RHS suggests the use of biological controls to avoid killing beneficial insects. Information from RHS website www.rhs.org.uk

Marion Kinns,

What is the difference between Rhododendrons and Azaleas ?

“Azaleas are all now all classified within the genus Rhododendron although historically Linnaeus put them into distinct genera. When he devised his system of classification, very few rhododendron species were known.”

*Azalea. Rhododendron ‘Daviesii’ Flower with 5 stamen*

By the 1920s, large numbers of species were being introduced to cultivation. A new classification system was devised by Sir Isaac Bayley Balfour (RBGE), though still following the binomial system of Linnaeus where each plant was included within a genus followed by a distinct species name. Different rhododendron species were grouped into series.

Further changes, proposed initially by Sleumer in 1949, led to the gradual adoption of a new system in which rhododendrons were grouped into subgenera, sections then subsections. This was as a result of the discovery of new species and increased understanding of the genus. DNA analysis is now allowing other adjustments to be made to their classification.

This latter system is generally in use today. Plants which are known as azaleas in the horticultural trade are placed within the subgenera Azaleastrum and Pentathera. None of these have scales i.e. they are elepidote.

“One difference of note between so called Azaleas and other Rhododendrons is that the ‘Azaleas’ have 5 stamens per flower and Rhododendrons have 10 or more.”

*Rhododendron ‘Madam Mason’* *with at least 10 stamen*.

Author : Marion Kinns 2024

Footnote: Details on Rhododendron classification can be found on the American Rhododendron Society website.