Monday 28 October 2013

Gardening transformed. Herbaceous borders do not have to be high maintenance.

Even when planted this border has never been dug

I have hundreds of square yards of herbaceous perennials in my four acres of cemetery gardens which I maintain with an average labour input of two hours per week. I use some of my methods in my own herbaceous borders.
My friend Isobel had magnificent herbaceous borders. As she gets older - she is younger than me - to reduce garden maintenance, she is converting to growing roses! I am very pleased about this because as a result she has given me some magnificent herbaceous plants. Her superb peak season, colour co-ordinated borders, hugely acclaimed on her Open Day, used to take many hours to maintain. 

Why herbaceous borders are traditionally high maintenance.
It is important before you plant a herbaceous border that you eliminate established perennial weeds. Most gardeners fail to do this and subsequent weed control becomes nye impossible. Many gardeners accept divisions of herbaceous plants riddled with couch and ground elder from ‘kind friends’. These weeds have a way of taking over.

Most gardening books advise deep cultivations before you plant, to dig in huge barrow loads of farm yard manure and to leave fallow for the first winter before Spring planting.
Weed control in traditional borders involves laborious forking and hand weeding (or hoeing under more enlightened management). You might not believe this, but some gardeners actually dig their borders in Autumn!

Most gardening books recommend replanting every three to five years. Absolute nonsense, but I can understand why when rubbishy lanky spreading mildew ridden michaelmas daisies wander all over the place and lupins self seed vigorous purple offspring. Don’t get me wrong, many varieties of asters are my very favourite plants. I love lupins too but they are  very high maintenance. There is a ridiculous idea that clumps need to be divided because their centers become moribund. Once in a blue moon this will be true but I have yet to divide a herbaceous perennial for this reason. Of course vigorous plants do have a tendency to out grow their space and need to be reduced…
Some plants such as primroses and polyanthus do respond well to regular division. I grow these elsewhere in my garden.

Staking perennials is a skilled and time consuming job. Not only does inserting bushy supports need to be carefully timed and synchronised with plant growth they need to be carefully removed when the plant is cut back in Autumn. Some gardeners insist on staking all their herbaceous  plants. I remember years ago in a famous park in Leeds where even Dicentra formosa was supported. As holder of the National Collection I shuddered.

I do not stake any herbaceous perennials plants in the cemeteries but of course it does not matter if they flop everywhere!

Cutting back is an extremely labour-intensive task and if as I do, you believe that every ounce of beauty should be extracted from your plants before you prune back, the process needs to be spread over a long period.

Many herbaceous borders are riddled with powdery mildew, have slugs on the hostas, caterpillars and aphid. I never spray  against pest and disease in my herbaceous borders but many gardeners find this necessary… 

And we have not even considered watering, adding organic matter and feeding!  All this angst and hard labour. And after three years you need to do it all again. Not for me, thank you.

Better quality borders with much less labour.

On a new site eliminate perennial weeds before you plant using glyphosate. If in a new garden this takes a whole season start a lifetime’s policy of not letting germinated weeds seed.
Do not cultivate other than to adjust levels. Unless it is compacted by previous bad management do not disturb the existing soil profile at all. I am particularly addicted to making new borders by direct planting in a grass sward killed a few weeks earlier by a glyphosate spray. Why destroy wonderful  soil structure? I have been planting into dead lawns for clients and in my own gardens for many years now!

I am planting Cathi’s garden next door and am reshaping the borders to ease mowing

Best to plant in early Autumn and get the plants off to a good start in warm soil. However  where necessary and with appropriate management you can plant anytime. The only time I water my plants is when getting them established. I never water my established borders but of course in a very dry summer period an occasional very thorough soak with more than an inch of water is a beneficial option. Never faff around watering established plants with frequent applications of small quantities of water.

You must of course design your borders. Personally, I am incapable of drawing but do have the advantage of having a large stock of plants and divisions - knowing my plants intimately, I design as I plant. You will never get things completely right the first time and be prepared in the first few years to make small adjustments. This is best done at the time you can see something is wrong.

I am pathologically opposed to staking. I never stake plants in my cemetery gardens and  at home I can count on the fingers of one hand the occasions when Brenda insists that a delphinium, helenium or peony is given a cane or a loop of string. I prefer to plant bold self supporting clumps that grow sturdily in good light. Plants drawn as a result of poor light due to close proximity to buildings and hedges or planted in too narrow borders might need supporting in some gardens. I admit I am lucky to be able to plant in large self supporting clumps. Where small clumps of tall plants are planted, staking is more likely to be  needed. My garden has no special wind protection and is very windy. My plants grow sturdily in response to wind stresses right from first emergence and stand like soldiers even in gales. After exceptional very heavy wind it might take a few minutes to tidy the odd broken shoot but this will be no more (and frequently less) than those gardeners with their mental crutch of a crutch!

 None of these perennials are staked

It would be a shame to stake elegant Verbena bonariensis

Excellent weed control is fundamental to low maintenance borders. Throughout this blog I extol a ‘little and often’ approach to weed control. In my glyphosate post last week I described specific aspects of timing and directional spraying to make weed control in herbaceous borders efficient and easy. In my own borders I spray around herbaceous clumps with glyphosate and if necessary, hand weed amongst delicate new shoots. I sometimes lightly hoe. 

Some herbaceous plants such as helianthus and eupatorium are thugs and without appropriate attention tend to take over and swamp less vigorous plants. You need to adjudicate in this battle. I frequently do this by chopping out pieces to plant elsewhere. Sometimes this is insufficient. A weed is a plant in the wrong place and where my herbaceous perennial has spread too far I spray its invading advancing front. I am totally ruthless but a visitor to my garden is unaware that I sprayed early in Spring as shoots emerged or sprayed portions of the tops at the end of the season a few weeks before the plant’s natural senescence. 

Emerging spring shoots of helianthus have been deliberately sprayed and will die. If I have fastidious visitors I can hoe these yellow shoots off now. Do not try this with delicate plants.

This simple example is on ‘Gardeners Garters’ in late Autumn, the method is of greater value on thuggish miscanthus and elsewhere, bamboo! The dead sections make nice autumn colour!
I generally try to avoid planting pest and disease prone plants and am remarkably tolerant of light infections and await normal health to be restored by natural control as predators and parasites devour pests such as aphids. Because my borders are mainly island borders they receive plenty of light and do not much suffer from fungal disease. Other than my glyphosate I never spray!

I have been trying to convince readers that minimum cultivation creates very healthy soil. I hardly ever find it necessary to fertilize herbaceous  plants. Should your soil be less fertile than mine, top dress with general NPK fertilizer - perhaps in March. Just scatter it, don’t damage the soil and plant roots by working it in!

Cutting down herbaceous borders with secateurs  at the end of the season is very hard work, back breaking and boring. I have been cutting back with a petrol driven hedge cutter for many years now. The technique is now starting to become popular in public gardens. I find I can cut very close to the ground and get a very tidy finish. In my cemetery gardens I shred the tops as I cut and leave the trimmings as a mulch on the surface. Management here does not permit this untidy refinement which I only get away with in parts of the garden Brenda rarely visits. You will probably be horrified that sometimes I flash burn the cut tops in situ on the surface of the border. I would argue that the char is beneficial..

Before and after

At Boundary cottage my herbaceous borders are at least ten years  old. They will outlive me before they need replanting.

It would not be as much fun if I did not sometimes add a few extra plants

Wednesday 23 October 2013

(7) Using glyphosate selectively; selectivity by timing

 As an annual the  poached egg plant will die in July. It will be an opportunity to spray and give self sown seeds a clean start
I make the usual provisos that glyphosate is not selective in itself. It does not distinguish between a plant and a weed. You make that decision when you spray. 
Selectivity by timing relies on your plant being dormant when you spray glyphosate on growing weeds.

Particularly relevant to my theme today is that glyphosate in normal circumstances only acts through the leaves and other green parts of the plant. It does not kill plants lying dormant below the ground and for normal practical purposes does not wash into the ground and leave residues that will damage future growth.

Glyphosate is translocated through the leaf to kill the root. It is useless against chopped up little pieces. It needs an intact growing weed and it is of no value to zap a weed like convolvulus when it has just emerged from the ground. Weeds need plenty green foliage to be killed. A well timed spray to an intact vigorous weed like couch or convolvulus in favourable circumstances will kill it in one go. It is more common however to have to repeat spray some weeks later.

This post is part of a series. I do not want to persuade inexperienced users to follow my methods Certainly not until they have read my previous posts. Insert ‘glyphosate’ into my search box to find out more.

Selectivity by timing
The obvious example of this is spring bulbs that die down in summer. Daffodils for example might be growing in a stand of luxuriant perennial weed. You can safely spray when the bulbs have died down. I have written before about the thousands of daffodils, snowdrops and bluebells which when released from the yoke of ground elder, couch, horseradish and nettles returned to their former glory in my churchyard gardens. The same principle applies to any bulb that goes dormant whenever in the year this might occur. Hardy cyclamen for example lose their leaves between March and  August. It is safe to spray then.

Selectivity by timing can be used on any garden plant that dies down and goes dormant. Many herbaceous perennials die down in late autumn. Even nasty weeds like couch if undisturbed when entangled at the base of a dormant perennial will succumb to glyphosate as late as an December application. You cannot do this amongst those herbaceous perennials that in autumn are already making new green basal growth. 
You can often further increase your window of opportunity with herbaceous perennials that are becoming senescent by prematurely cutting them down to the ground. This comment applies to where you might have a severe problem. I would never normally cut plants back early for routine control of weeds.

A slightly different aspect of selectivity by timing is to spray at the end of your crop. It is appropriate in the vegetable garden to spray to ‘clean up’ between crops or in the winter if the land is fallow. Slightly more subtle in the ornamental garden is where annual plants like limnanthes, nigella and Nemophila ‘Penny Black' naturally die and there is a window of opportunity of a few weeks to kill weeds before self sown seeds germinate. You can even anticipate this event by spraying a little early. 
For some of you, limnanthes may be the weed and you can spray it anytime! On a slightly different note where a plant from seed is as prolific as limnanthes it matters little if there is some collateral damage when you spray.

Nemophila ‘ Penny Black’ No weeds here, it had a clean start
This love-in-a-mist will have already self seeded. I am in no hurry to remove it as I like the dry seed heads. Nasty milkweed has germinated below. I can safely spray it.
Some of the examples I have given involve spraying in late Autumn or Winter. It surprises me how many gardeners do not take advantage of spraying green weeds at this time of year. Yes, the glyphosate is much slower to kill, but against new weeds from seed it is extremely effective at this time when the soil is wet and hoeing is useless. Where plants such as hosta, agapanthus and phlox and indeed most herbaceous plants completely die down you can spray with complete freedom all winter. Where perennial weeds are as  dormant as the plants however glyphosate will be of no value! Take care not to spray un-noticed small Spring sprouting shoots that  are about to appear.

Seasonal variability in plant’s sensitivity to glyphosate

  • There is considerable variation in the sensitivity of different plant species to glyphosate.This will be the subject of a future post.
  • I am assuming in my comments that you are carefully directing your spray and are attempting not to contaminate your plants. These paragraphs are about the degree of care that you need to take.
  • If you spray a large plant thoroughly with glyphosate it will usually be severely damage and in most cases you will kill it. Because of the translocated nature of glyphosate, if killing is your intention, it is not necessary to completely cover all of the leaves, but the better the cover, short of ‘run off’, the more successful you will be.
  • If a large plant only receives a little unintentional drift the proportion of leaves that receive herbicide is small. Such plants will often have sufficient resources to be  undamaged. The corollary of this is that small plants are at much greater risk.
This large eupatorium and helianthus will not be damaged at all by a tiny amount of drift
  • Although I have emphasised in previous posts that it is no use zapping a perennial weed as it emerges when most of the weed’s volume is the roots in the ground, do not be complacent  and assume the same is true of your emerging herbaceous plants. Although it will not kill them, many herbaceous perennials are extraordinarily sensitive as they emerge from the ground. Plants such as Aster novae-angliae, A.amellus, A.frikartii and phlox are liable to be checked and show unacceptable chlorosis.
I have been caught out and damaged  some of the shoots on this aster novae-angliae 
I am thoroughly ashamed of myself. The level of damage on this phlox is completely unacceptable. I must have been somewhere else when I sprayed! Perhaps it was windy?
Even after this desecration, from June the flowers were magnificent!
  • When young plants are making luxuriant active growth and their tissue is soft they are more likely to be damaged. For many delicate green plants including most vegetables, it is never safe to spray among them. I am particularly cautious when spraying my borders in spring and early summer. I am less careful in summer and by late autumn when plants start to become senescent I become positively complacent.
I am particularly careful when I spray at this time
  • Senescence is when plant tissues start to age and leaves turn yellow and brown. I find that damaging translocation of glyphosate to the roots is now minimal.This is at variance with some conventional opinion where ‘old generation’ hormone weedkillers were found to work best when applied to leaves of plants just before they senesced and started to translocate stored food reserves to the roots. Personally I have never found senescent plants to be particularly vulnerable to glyphosate. I find many herbaceous plants start to become more woody late in the season with fewer leaves at the base and I can less carefully spray. With plants such as my asters and phlox which are so sensitive in Spring, by late September provided I direct my nozzle downwards and close to the ground I find I can safely spray very near to a clump - even below the leaf canopy where I cannot see the weeds!

It is late September, my phlox has been flowering for all of three months. I am completely confident I can safely spray these grassy weeds if the spray head is low
I tend to direct my comments to herbaceous plants which are my passion. The same principles apply to shrubs which in general are more easily managed under a glyphosate regime. Because shrubs have a woody base and often a high canopy of leaves they are less likely to be damaged when you carefully spray. Spray that alights on mature bark of a woody plant is unlikely to be absorbed. This does not apply to green basal shoots on woody plants, nor to the green stems of roses. 
Some unexpected shrubs such as thuggish cultivated blackberries and hybrid berries or ornamental elderberry are surprisingly sensitive. I know to my cost!
When deciduous shrubs have dropped their leaves it is particularly safe to spray. 

Mingling. A few mixed messages
I am told the next horticultural fashion is ‘mingling’. You can see from the mingle-mangle below that much to Brenda’s scorn, I have a liking for mingled plants! Here in Bolton Percy cemetery you see a ground cover of Lamium galeobdolon, pulmonaria, ornamental strawberry and infiltrating wild garlic. For thirty years it was under very heavy shade as you can see  from the sculptured stumps of previously very large trees.

The patch can be used to illustrate a few points about using glyphosate.

A mingle mangle
1.If you start by killing all perennial weed the canopy of your plants does much of the the work of controlling weeds from seed.
2 It would be impossible to spray within clumps without causing damage, but the margins of clumps can be sprayed to keep weed free and to halt the spread of over-vigorous plants.
3. If I decide in a few years time that the garlic is becoming too much I can carefully spray the garlic when it is at its most luxuriant before it flowers (it would take all of two minutes). There might be some collateral damage but my vigorous ground cover will quickly grow back and nobody will notice.

The most significant timing of all  
I am afraid it is a council of perfection but where achievable it is really important. The best advice you can give anyone with a new garden or allotment is to get rid of the established perennial weed before they start.

Friday 18 October 2013

Wet soil science

Field capacity theory

I originally prepared this post last year when I was new to blogging. As someone innocent and pure in heart with a soil science message I was quite pleased with my effort…
You can’t publish that I was told in no uncertain terms. Mention was made of ‘Fifty Shades of Grey’; what on earth did they mean? “Juvenile humour” I was told. How appropriate from one who has entered his second childhood from his first without any intervening period! Publish and be damned! My original piece  was un-illustrated. I have learnt in my year of blogging  that pictures help to make one’s real meaning explicit (oh dear, there I go again). There will be no pictures of me bathing!

In the bath with my toy ducks

Lying in the bath my thoughts inevitably wander… to soil water holding capacity. My hand idly goes to...  a small rectangular bath sponge. I gently lift it out of the water and hold it horizontally. Water immediately pours out. If I continue to hold it steady, no more water drains. Is water in the soil like that?  Yes!  Growers would say my sponge -representing the soil -  was at field capacity. The water that spills from the sponge as I picked it up equates to drainage. No more water falls from the sponge as I continue to hold it steady, even though it is still very wet. Is a soil like that? Yes, no water drains from a soil that is only at field capacity.

I take my empty coffee cup and gently pour a little water over the still horizontal sponge (Damn, I need an extra hand). An equivalent amount of water drains from the sponge.  Soil water behaves like that. Soil normally needs the winter rains to restore field capacity before it loses water to drainage. Not this year, (this was 2012) our soil, unusually for summer, is still at field capacity and when it rains, it drains! How topical! How tropical?

I suddenly sit up really excited now. What if the sponge was compost in a seed tray or a plant pot? I experience a moment of acute revelation as I gently tip the sponge from the horizontal to the vertical and water cascades out. The depth of the sponge has affected its ability to hold water. Eureka, compost in thin layers holds a lot of water at field capacity, more than the same compost in a deep container. If the compost holds less water it is better  aerated.
I examine the still vertical sponge closely. It is much wetter at the bottom than the top. Compost in pots is the same. Maybe old fashioned crocking of pots wasn’t so daft after all! 

Sponge held steady on a horizontal axis. It’s holding a lot of water but none drains away
By tipping the sponge the vertical profile becomes deeper and lots of water rapidly drains away
Water ceases to drain when the quantity of water settles to the lower field capacity of a deeper profile. But look the base of the profile is wetter than the top! Does water in a pot behave like that?
Excited now, I squeeze the sponge and water runs out. Perhaps my squeezing represents the plants as their leaves transpire, sucking water from the soil. Perhaps it also represents the water that is lost by evaporation from wet soil.
Squeezing the sponge a little harder, I only get a little dribble. I squeeze really hard, no more water. But the sponge is still wet! Soil is like that, the plants cannot exert enough root pressure. Clay soil hangs on to as much as half the original water it was able to hold when at field capacity. Plant roots cannot squeeze hard enough to extract it.
I relax and sink down in the bathwater, still pondering that when I water a plant in a container I will raise the compost to field capacity. If I generously water, as I usually do, the surplus rapidly drains away.
What if my plant pot was in a saucer and the water had nowhere to go? The compost will be water-logged. It will be above field capacity and will be poorly aerated. I sag deep into the bathwater with a quiet shudder.

By this time I have got goose pimples and resolve next time to take a shower.
I used to use this analogy to my students. One year they presented me with a set of red toy ducks at the end-of-course alcoholic celebration!

Now what does the water that leaks from the wet sponge represent when my hand trembles ….? Maybe  a soil scientist will post a suggestion.

I get out of the bath and go to play in the garden

To carry out my experiment I need to make a slit in the bottom of my plastic tray
I fill a seed tray with compost and thoroughly water it.. and again… and again, to demonstrate that it really is at field capacity. At each watering surplus water drains. I leave the seed tray for about a quarter of an hour. Because it is only at field capacity no more water drains over this time.

I convert the shallow tray to a deeper profile by tipping it. Oodles of water rapidly drains away
Just look at all that water lost from the seed tray
I have made a slit in this pot and filled it with sand and thoroughly watered it to examine the profile after drainage. It is wetter at the base than the top.

Practical significance of field capacity theory.
I used to refer to field capacity in a pot or a seed tray (or a sponge for that matter) as ‘container capacity’. A growing medium in a shallow container will have a higher field capacity than the same medium when it is part of a deep profile such as in the ground.
  • In a normal season in the UK, soil in the ground wets up overwinter and is restored to field capacity. Only then will further rainfall run away to drainage. February is not called ‘February fill-dyke’ for nothing.
  • Because a great deal of water per unit volume is held at container capacity, garden soil will often hold too much water if used in containers and will be poorly aerated. Seed and potting composts are formulated with ingredients that are well aerated when at field capacity.
  • Shallow seed trays hold a lot of water after watering. A good thing for a tray of vigorous water hungry bedding plants but not so good for small seedlings if you water  too often.
  • Some gardeners cause themselves endless problems by economizing in the amount of compost they use and sowing or pricking out into only half filled trays. The compost lies too wet.
  • The real reason that some plants are found to do better in deep containers (e.g sweet peas are often sown and grown-on in ‘long pots’) is that the growing medium is better aerated after watering.
  • The reason that outdoor plants in shallow display containers frequently die in wet weather is that they are badly aerated when they remain for a prolonged period at a high container capacity.
  • Thin layers of ‘amended’ soil in the ground, especially when overlying a gravel drainage layer(!) may hold excessive amounts of water and be poorly aerated. Such a gravel layer provides an unfortunate discontinuity to capillary water movement down into the soil.

Definition of field capacity

A soil is at field capacity when it holds all the water it can against gravity assuming free drainage.  

Container capacity is a term used by some growers to refer to the field capacity of a growing medium in a container - or a block of compost - or even a sponge!

I failed with this experiment to demonstrate clearly that water levels at the base of a soil profile is greater than at the surface. By now some of you will have decided I am somewhat mad. I present you with evidence - I make mud pies. Guilty m’lud as charged.

Sunday 13 October 2013

Garden myths discussed. A modern meme

Rhododendron ponticum is allelopathic

When I read the popular press I learn that Scotland  and Wales has been taken over by Rhododendron ponticum and Japanese knotweed, not to mention bracken. In my previous post Peter Williams eloquently described how a hybrid swarm (I love that phrase) called R. x super-ponticum is extremely invasive. It smothers adjacent plants and on wet Welsh hillsides and pastures starts to take over. I know that Peter considers this rampant vigorous plant when in its optimum growing conditions has the botanical resources to be a complete thug. On a related theme my botanist friend, Mike Ashford tells me that in his lecture on ‘the functions of leaves’, if he is feeling provocative he declares that leaves are a weapon! They enable a plant to overgrow and swamp their neighbours. As gardeners we know that it is sometimes appropriate to snip off a few leaves to restore a balance of power between competing neigbouring plants.

Rhododendron x superponticum  A real threat to the environment but perhaps overhyped?

Varieties of true Rhododendron ponticum growing in a parkland are not a threat to nature
I recently read in a popular garden magazine that Rhododendron ponticum is allelopathic. That means that it exudes toxins into the soil which enables it to suppress and outgrow other plants. I complacently filed this information away at the back of my head. The idea is completely plausible and indeed those other two thugs, bracken and Japanese knotweed really are allelopathic. I mentioned this to Peter who is both an expert on rhododendrons and allelopathy. He was not aware that ponticum was allelopathic and as a good scientist made no further comment.

Memes are information that pass from one person to another and like Chinese whispers a story becomes somewhat garbled in transit. It only needs someone to suggest that ponticum is so invasive that “it must be allelopathic” that it quickly becomes “ponticum is allelopathic”. If the next person in the chain is horticulturally authoriative, is even titled, or worse, mentions it at a horticultural conference and it gets into the popular press it becomes a horticultural fact. It must be true.

Now personally I have no idea whether or not we are dealing with a myth. Rhododendron x super-ponticum is an amazingly aggressive plant which does suppress and kill surrounding  herbaceous and scrubby vegetation and can survive under very dense tree cover such as in an oak wood. The story is all the more plausible because ‘super-ponticum’ does produce toxins that makes its leaves poisonous and unpalatable to animals.
Rhododendron has amazing powers of regeneration 

In an oak wood 
James Merryweather is an ecologist and botanist and coincidentally is a former scientific colleague of Peter Williams. He has investigated the notion that Rhododendron x super-ponticum is allelopathic and can find no evidence whatsoever that it is so successful because it exudes phytotoxins with which it kills neighbouring plants.
James Merryweather is actively involved in practical considerations of rhododendron control and measures that will help restore local ecologies in Scotland. A true return to original conditions is difficult for all manor of reasons. Not least is the loss of mycorrhiza and other beneficial soil living organisms and there will also be local loss of propagules of formerly colonising plants. James promotes a simple manual method of initial restoration. It’s called the lever and mulch method. This involves a fairly straight forward dismantling of the rhododendron and leaving cut branches on the surface as mulch.This is Infinitely better, cheaper and kinder to nature than scraping them out of the ground with great ugly bulldozers as sometimes happens!
Please read James’s beautiful prose as he elucidates his passion. I love his turn of phrase when he debunks the allelopathic story. He refers to a cautious speculation that has lead to a dogmatic factoid.

These rhododendrons were originally planted on graves in my cemetery garden in Barnsley a very long time ago.

They were cut back hard to the ground fifteen years ago - you can safely do this with all garden rhododendrons.
To find other gardening myths on this blog insert ‘myths’ in my search box

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

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