The Colour of Plants at Twilight

by Brian Denison

Some time ago Judi (Barton) asked me why plants look different at Twilight, so here is my definitive answer which I thought I would share with you. It’s all about the composition of light and light scattering.

Fig 1

Light is simply a collection of electromagnetic waves in the visible spectrum. Violet/blue light have the shortest wavelengths and red light the longest. Green, yellow, and orange are in the middle. These rainbow colours are shown in Fig 1.

When a ray of light travels through the atmosphere some of the colours are scattered out of the beam by air molecules and airborne particles, changing the final colour of the beam. At sunset when the path through the atmosphere is much longer, the violet, blue and green components are removed almost completely leaving the longer wavelength orange and red hues (fig 2).

Fig 2

In other words, light may be white or yellow at midday, gradually turning redder as it approaches sunset due to light scattering.

Evening sun is lovely, but twilight turns a garden into a place of enchantment. Colours that dazzled disappear and paler tones come to life. This is the time when white, pale yellow and light pink create really pleasing effects.

We also owe some more of our most spectacular phenomena to light scattering – not just the red of sunset, but also the blue of the sky, the white of clouds and not forgetting rainbows.

The sky is blue: we all know that, but why? Air molecules, like oxygen and nitrogen for example, are small and thus more effective at scattering shorter wavelengths of light (blue and violet). The selective scattering by air molecules is responsible for producing our blue skies on a clear sunny day (Fig 3).

Fig 3

But why is the sky not indigo or violet (shorter wavelengths than blue). This is because the sun emits a higher concentration of blue light waves in comparison to violet or indigo. Furthermore, our eyes are more sensitive to blue rather than violet hence to us the sky appears blue.

So why are clouds white? Cloud droplets have diameters of 20 microns or so (larger than gas molecules) and are able to scatter all visible wavelengths more or less equally. This means that almost all the light which enters clouds will be scattered. Because all wavelengths are scattered, clouds appear to be white. When clouds become very deep, less and less of the incoming light makes it through to the bottom of the cloud, giving these clouds a darker appearance.

Lastly rainbows (Fig 4), but refraction rather than scattering is the mechanism. Most raindrops are spherical, and it is this spherical shape and their size that provides the conditions for a rainbow to be seen.  Light passing from air to a raindrop at an angle slows and changes direction, in a process called refraction (fig 5). Refraction splits the light into the colours of a rainbow just like a prism. The sun’s position (angle) and that of the observer are particularly important, which is why rainbows are not seen so often.

I hope you have enjoyed the science!

Brian Denison

Plant of the Month: November

Saxifraga fortunei

by Sue Gray

Saxifraga fortunei

Had Covid19 not forced the cancellation of the AGS event, originally scheduled to take place at Harlow Carr on October 14th, I am sure that during the past couple of weeks I would have been planting some of these little jewels which I would have been unable to resist buying.  I say ‘little jewels’, and they are usually sold by nurseries specialising in alpine and woodland plants, but although some are grown as ‘specimen’ plants, largely for foliage effect, many are robust, very good garden plants which are extremely useful at this time of year.

Saxifraga fortunei was first introduced to Great Britain from China by the English Botanist William Jackson Hooker, and named for the Scottish Plant Hunter Robert Fortune, in the mid 19th century, and is native to China, Japan & Korea.  Whilst the species form has white flowers, there are now many named forms in colours from white, through various shades of pink, to darkest red.  I would describe them as ‘quiet plants’, almost the Autumn equivalent of hepaticas; you hardy notice the foliage emerging but when it becomes crowned with the delicate flowers, they are such a welcome sight at this time of year.

They are herbaceous perennials and, according to the official advice, prefer a shady, or part shady spot with the usual ‘moist but well drained’ soil. However, I find that by October, when the sun has lost much of its strength, few gardens can really be said to be in ‘full sun’ so S. fortunei can withstand a more open position, and this, now sadly unlabelled, plant (right)

performs beautifully in my garden in a relatively open spot.   From my experience, and this may just be me, I find that the white and pale pink varieties are more floriferous. 

S. fortunei ‘Reica’

The deep pink and red varieties are more dramatic with the flowers set against often dark foliage, but I find the flowers can be rather more sparse, as shown on this plant of S. fortunei ‘Reica’.   

When I started thinking about writing this, I got out my copy of ‘Plant Finder’ to check on some of the named varieties.  I expected to find them all recorded, in alphabetical order under the heading ‘fortunei’, but instead I discovered them all, in common with all other named varieties of other Saxifraga species, in alphabetical order, spread throughout the full list of Saxifraga entries, followed by (fortunei) and (5) so, for example the  entry for one of the best known varieties ‘Wada’ reads ‘Wada’ (fortunei) (5). Turning to the front of ‘Plant Finder’ I discovered that there are 15 classifications of Saxifraga; class 5 is entitled ‘Irregulares’ and describes plants in this class as ‘shade-tolerant, usually herbaceous perennials forming rosettes of broad, palmately lobed leaves, with leafless stems bearing lax panicles of small flowers with short upper, and longer lower petals, in summer or autumn’.

Shortly after discovering all this, I was in the company of a very knowledgeable friend and said to him, ‘explain to me, in words of one syllable that even I will understand, about Saxifraga classifications’.  He gazed into space, as if thinking ‘where do I begin?’, but then said, ‘I shouldn’t worry about it’, so I won’t, but just enjoy these lovely plants for what they are.  I am indebted to our Secretary Pat who has sent me some images taken at Holehird recently, and to a friend with whom I was visiting Harlow Carr and who photographed various examples on display in the Alpine House.  Their images appear below.

You may not be surprised to hear that, having spent some time thinking about these lovely plants, I think I can accommodate several more in the garden, and an order has been sent off to one of my favourite nurseries!

Yorkshire Arboretum

An Autumn visit – 20th October

by Sue Gray

On a gloriously sunny, balmy, afternoon today, I was privileged to visit the Yorkshire Arboretum at Castle Howard.  There are big changes afoot with a new building under construction which will accommodate the UK’s first purpose built ‘Tree Health Centre’ and, like many other places, due to Covid19, the Arboretum was closed for a period earlier in the year but it is now making up for lost time with pre-booked visitors enjoying the glorious Autumn colours.

If you have never visited the Arboretum, now and in the coming weeks is a wonderful time to do so; the café is open from 11am serving delicious drinks and light meals.

Below are a few images of the sights that await you.

And here are some of the individual plants that caught my eye

The aptly named Acer rubrum ‘October Glory’
Prunus incisa – the Fuji Cherry

Sorbus ulleungensis ‘Olympic Flame’
Carya tomentosa

Sue Gray

October 20th, 2020

Plant Forum – October

We missed our Plant Forum in August, like so many other events in this year of Covid-19, so it is proposed that we have some virtual ones! For October, please send your nominations, suitably illustrated, for the best Autumn colour, be it tree, shrub or perennial to

Sue Gray has started the ball rolling with her nomination for Euonymus alatus – the Burning Bush

Euonymus alatus

Acers are always reliable purveyors of autumn colour, but this one in the Hackett garden, is better known for its winter bark – Acer palmatum ‘Sango-kaku’

Acer palmatum ‘Sango-kaku’ – the Coral-bark maple

Pat Gore says: “What a difficult choice! I have some lovely Acers, a Rhys typhina dissecta, a butter yellow Morus nigra – all of which give a great autumnal display.

However, I would like to nominate Viburnum plicatum ‘Mariesii’ as providing my favourite Autumn colour. It starts to turn in late Summer and goes an increasingly dark wine red over the succeeding months. It also has a second small flush of flowers which look lovely against the dark foliage. The leaves are held until late Autumn and I would not expect them to fall until mid- late November.

I have a bird’s eye view of it when I open my bedroom curtains every morning so it gives me a lot of pleasure throughout much of the year.”

Viburnum plicatum f. tomentosum ‘Mariesii’

Terry Benton of Westbury, Wiltshire was a regular contributor to our lockdown gallery. Here’s his nomination: “The choice from my garden is Hesperantha coccinea ‘Major’. It’s not an unusual plant but the flowers provide a strong colour among the garden’s fading hues. I find them still standing proud and blooming long after the leaves have fallen from the trees.”

Hesperantha coccinea’Major’

Ann Fritchley offers the Crimson Bromeliad – Fascicularia bicolor.  “Unfortunately”, she says, “the pale blue flowers in the centre have gone over”. Still pretty exotic for October!

Fascicularia bicolor

Judith Ladley gives us an old and trusted favourite. “I would have sent a picture of Parthenocissus tricuspidata which has been superb but is now nearly finished.  Therefore I nominate Verbena bonariensis which self-seeds freely in my gravelled area.  In the background is Catalpa bignonioides ‘Aurea’ which has done very well this year.  I cut it back in Spring.

Verbena bonariensis

Judith Edmonds picks an Acer: “Here’s my vote for autumn colour: Acer Palmatum ‘Chitose-yama’. Seen at the Himalayan Garden & Sculpture Park, Grewelthorpe, last week. As well as the dramatic colour, I thought the leaves were also a very beautiful shape. It’s definitely on my wish list now! Having checked it out on the RHS website I see it has an AGM and the leaf colour earlier in the year looks good too.”

Acer palmatum ‘Chitose-yama’

Kate van Heel’s nomination is Polypodium cambricum ‘Richard Kayse’. She says “It’s a winter growing fern that is a fabulous lime green at the moment”

Polypodium cambricum ‘Richard Kayse’

Katherine Hill offers two contrasting takes on autumn colour

Holehird Gardens

An Autumn visit – 16th October

by Pat Hunter

This is a garden I regularly visited up to my teenage years as my Mother loved a visit and the May plant sale was a definite date on the calendar.

The view over Windermere

The setting is superb, a sloping site looking down to Lake Windermere and across to the Lakeland Hills; put the Autumn tree colours in the foreground and the views are stunning.

Distant fells

A visit usually starts by going into the walled garden next to the car park. This is full of Autumn classics, Rudbekias, Dahlias, Hesperantha, Leucanthemella serotina, Symphyotricums in abundance as the herbaceous perennials.

The walled garden

Display house – succulents

There is a display greenhouse now against one wall, this has not been there that long in the great scheme of things. It contained a cacti/succulent display, a beautiful Lapageria rosea on the back wall and an A4 piece on the problems that the Lakeland horticultural society has had with whitefly control in the display house and how they have changed the plants and the whitefly regimes to cope.

Lapageria rosea

After the walled garden, a walk through the alpine and Tufa houses to the superb limestone rockery area. I couldn’t help but take some pictures of superb Saxifraga fortunei, as Sue Gray had been talking about these the night before.

The rock garden

The Ponds

After a couple of circuits of this side of the garden, it was down past the ponds to the woodland walk, which takes you down the drive to the Lakeland collection of Hydrangeas.

The Hydrangea Collection

This is the best time to visit. I was blown away by the superb row of Hydrangea paniculata.

Hydrangea paniculata
Hydrangea involucrata ‘Hortensis’

And finally, the seat – how many seats do you see where the arms are snakes, not just any snakes but snakes with ‘pucker up’ lips!!!!

Pat Hunter

October 16th, 2020

Zoom, Zoom, Zoom, we’re going to the….

Gardening in the 21st Century – a zoom talk by Timothy Walker

a review by Carine Carson

Well, if it was a Monday or Tuesday and one of my ‘Grandma Carine’ days, it would be to the moon!  However, in this instance it is to the bijou study in my bijou bungalow in Wetherby to hear Timothy Walker, our first Zoom speaker for WYHPS during this time of the Covid pandemic and various social distancing and lockdown measures.

Before I get to Tim’s talk it seems appropriate to say something briefly about Zoom.  I think that, in common with the rest of the population, almost none of us had heard of Zoom before lockdown 2020.However, thanks to the younger members of our families wanting to maintain visual contact and setting up family quizzes etc, we were forced to take the plunge.  It has been a steep learning curve for us all, but, as with the other evening, people are prepared to have a go and those of us who are just one step ahead are happy to chip in with the odd bit of knowledge we have. I feel we all managed incredibly well and I’m confident we will soon be telling other members how straightforward it is to negotiate zoom.

I also thought that Zoom worked really well in the context of a WYHPS evening meeting.  No one had to negotiate the Leeds traffic, come out in the cold and dark (if that is your issue) and some members even managed to make the whole event even more enjoyable with their favourite tipple to hand!  I for one enjoyed being able to sit at the desk in my study and make notes instead of scribbling in the darkness of Paxton Hall.

I was one of the really lucky people who had never heard Tim speak before and so the evening was a wonderful revelation to me and an introduction to a truly inspirational speaker who delivered his talk in an extremely entertaining manner (never known a garden speaker to squeeze in so many naughty words and phrases – more below) and Tim was certainly someone who wore his knowledge lightly.   As most of you know, I am the ELC (early learning centre) branch of the HPS so forgive me if I have missed important technical details of Tim’s talk and I can hear you all saying -we are all learners – well can I just say, some of us have more to learn than others.  Here goes anyway.

Tim led us through his ten pieces of advice for gardening in the 21st Century.  He started with our soil, about which he warned us, although we can improve it, we cannot change it!  He advised on how you might improve the soil, for a herbaceous border this is done in February, and in various ways – notably by adding nutrients such as a general organic NPK fertiliser, such as Growmore.  Tim told us of an infamous border in which he had employed the extreme measure of double digging (historically known as b**tard-trenching) and from the morning after was henceforth known as the b**tard border!

Tim’s second point was to choose plants that like your soil and his motto now is ‘if at first you don’t succeed, sod it!’ There speaks a man of experience. However, Tim did point out that we shouldn’t be too quick to dismiss plants that wouldn’t appear to be able to thrive on our soil – the acid/alkaline issue.  Here he spoke most lovingly of the winter-flowing shrub, Hamamelis mollis, whose perfume apparently makes Chanel no 5 smell like Dettol. Also on plants, Tim’s next point was to make use of native plants like Honeysuckle which is great for supporting moths.  He waxed lyrical about Viburnum opulus var. americanum ‘Compactum’ which has gorgeous flowers and the bonus of beautiful berries in winter.   Two further points on plants encouraged us to grow fruit and veg and to raise new plants in loam-based compost.

Tim then addressed his concern about watering and informed us he aims never to water except when planting.  His recipe here is to dig the hole and half fill with soil, firming it well around the roots of the plant and then topping up to the brim with water, which you allow to sink in before back-filling with the rest of the soil but not firming this in as much, to encourage the roots. Some call this puddling!

Tim’s next piece of advice was not surprisingly to avoid using pesticides, favouring alternative means of control – with his Hostas, for example, he goes for copper tape collars on his pots.  As I have no water feature in my garden to help with the slugs, I keep all mine in pots and use sharp grit.  I also use nematodes in the soil in spring but if some of you are feeling really brave you might go for the ‘Scandinavian cannibal slug method’ as recommended in the current issue of Cornucopia.

There were three further pieces of advice from Tim.

First,  that climate and weather is just a great unknown – thank goodness for a clear piece of advice at last!  Whilst he recommends Sir David King’s book: A Hot Topic, Tim’s conclusion, as a respected scientist is that it is impossible to know what will happen and what will grow. Don’t you just love someone who gives an honest answer!

Meanwhile we should join our local Wildlife Trusts and Plant Heritage to support conservation.  Tim suggested we also get involved in planting hedges in our own garden, in a community garden or on our estate (I don’t think he meant the variety that runs to our own personal hundred or so acres!).The best thing we can do is to get young children involved – they are our gardeners of the future.  Although, for those of us who are grandparents, we might want to practise a little more health and safety than Tim apparently did with his children – and I was certainly reassured that he was speaking about them all in the present tense – so ultimately the gardening bug has done them no long lasting harm!

And finally, who didn’t laugh when Tim put up a couple of photos of combinations of rhododendrons in flower and uttered that memorable quote – ‘people who grow rhododendrons are colour blind’! He did qualify this slightly but it did make me laugh.  So, all in all, if the looks on people’s faces and the comments people made at the end of the talk are anything to go by, we all thoroughly enjoyed our first zoom speaker and Tim will be a hard act to follow.

A great start to our Zoom future – hope to see more of you next time with or without the wine!

Carine Carson

October 2020

Harlow Carr – autumn colours

by Carine Carson and Pat Hunter

Although the weather was far from perfect, Thursday 15th October was just the sort of day to attract WYHPS members to Harlow Carr in their droves – well, at least two!

Carine and Pat were kind enough to send some pictures of the day for the website.

Carine first – she says:

“Harlow Carr was just magical today – a real profusion of stunning autumn colours and textures. The Acers and Euonymous Alatus stole the show.

I didn’t get long to enjoy the garden before the heavens opened. It was just lovely for the hour I had to wonder through the winter garden and the improved and extended rock garden.”

Pat Hunter was also very taken with an Acer, preferring the back view to the front!

Acer – front view
Acer – back view

Pat was also intrigued by the Flouroselect trials of one of her favourite plants, Rudbeckia hirta. Here are two of them:

Pat commented: “My all time favourite is Rudbekia triloba ‘Prairie Glow’ but I grow this one, so no picture!”

And finally, it was good to see that not only WYHPS members were braving the weather. Pat spotted this Comma butterfly on a single Dahlia

Lockdown Activities 2020

by Brian Denison

Back west corner with Hosta baskets, 19 May 2020

The garden has satisfied my needs during lockdown both mentally and physically. I completed a number of projects, the first of which was to build a Hosta display on the trunk of a chopped down.

The second was to rejuvenate a very shady bed.  The Sasa bamboo is well established but the area now features a new plant arrangement including Campanula glomerata, Kirengeshoma, Pleioblastus viridistriatus, Pulmonaria ‘Diana Clare’, Saxafraga ‘Rubrifolia’, Persicaria virginiana ‘Painter’s Palette’, Dryopteris wallichiana and Hostas. I am particularly pleased with the Hosta ‘Elvis Lives’ and Hakonechloa combo in the hanging bowl to the right.

Sasa bamboo bed, 16 June 2020

My next project was to make use of some large rocks recently excavated from the soil. I used small plants so that the rocks were not obscured, primarily Hosta ‘Blue Mouse Ears’, Hosta ‘Cracker Crumbs’, Bugle and Lamium.

New rocks, 26 June 2020

The bed is East-facing, so also somewhat shady. The rocks form part of the border shown in the picture below.

Wide view of west side of back

To the right of the rocks is a combination of Ligularia ‘Britt Marie Crawford’ and newly acquired Peucedanum ostruthium ‘Daphnis’.

‘Britt Marie Crawford’ and Peucedanum

Just behind the rocks is the new to me plant, Filipendula purpurea on the right.

Filipendula purpurea, 26 June 2020

The picture below is taken from the rock display looking west and features Helenium ‘Moerheim Beauty’ in full bloom in early August.

Back view from the Pieris bed, with H. ‘Moerheim Beauty’

The small bed to the right is nearer the house and features a newly acquired Crocosmia ‘Severn Sunrise’ with Solidago ‘Golden Dwarf’ and Astilbe.

Crocosmia ‘Seven Sunrise’, Solidago, Astilbe combo

Rocks were also used in the front garden as shown in the next picture which features a Rudbeckia hirta ‘Rustic Dwarfs’ plant grown from seed. A free packet of the half hardy annual came with Gardeners’ World Magazine.      

New path to Clematis ‘Broughton Star’

The rocks are sited in the corner of the wider view shown here, and you may have noticed the Cornus controversa ‘Variegata’ in the large pot.

Front garden

This is the main border in the front garden in July, but it is soon to be decimated because some plants are in desperate need of division and a couple are smothering more choice plants.

Front garden, main border

5 October – Work has just begun:

Front border refurbishment begins!

Sadly summer is all too short but I am still hanging on to one or two displays, such as a pot of Euphorbia characias ‘Tasmanian Tiger’ with Aeonium ‘Zwartkop’, Bush rose ‘Darcey Bussell’, Dahlia ‘Orange Turmoil’ and another Rudbeckia hirta ‘Rustic Dwarf’ with Phormium cookianum subsp. hookeri Cream Delight.

Hope to see you all next year, Brian

Plant of the Month: October

Allium cernuum – to buy or not to buy? That is the question.

by Sue Gray

I expect that, over the years, all of us have bought, or been given, plants that we have later regretted.  In my case the regret is usually associated with the performance of the plant, and how keen it is on world domination!  I think I am fortunate in having good loamy soil; I can claim no credit for this – it is what I inherited, which is as well as I am very bad at preparing soil for planting.  If there were an Olympic games for plants, I could nominate several plants for inclusion in a sprint relay, Silene fimbriata, Adenophora, Centaurea and some Phlox to name but a few, but in the main these can be controlled (with the exception of Japanese anemones!) by judicious digging out or, as a last resort, spraying with weed killer, but the ‘self-seeders’ are a totally different matter.

Allium cernuum

The plant that has been causing me particular anguish in recent years is Allium cernuum.  I know it is very attractive but it has got everywhere since I acquired it at a garden on one of our Group holidays some years ago.  I had decided that I would try and use as many bulbous plants as possible in one particular bed and, as they were so pretty, I think I might have even bought two pots.  First mistake.  I should have been ‘put on enquiry’ (as we used to say in my former working life as a bank clerk) by the fact that the garden owners had so many pots of it for sale; it has taught me ever since to be extremely wary of any amateur gardener with a lot of one particular plant for sale!  I brought them home, planted them, and over the years they have cropped up throughout the bed and in the gaps between the paving surrounding the bed.  Of course, they are no respecter of space and quite likely to appear in the middle of other established plants, as they have done in some clumps of, what I believe to be, Allium senescens.

Allium senescens

These alliums are much better behaved; they do not seed around but form clumps of semi-evergreen foliage about 25cms tall with slightly taller mauve flowerheads in mid/late summer.  As they bulk up so well, over the years I have split them and formed four good sized clumps, two in the front garden and two in the back, all of which had A. cernuum growing up through them.

I decided that the time had come to deal with the interlopers, but realised that to do so I was going to have lift all the clumps and try and identify which bulbs belonged to which allium.  As a first step, when the flowers of A. cernuum appeared, I cut the head off, thus hoping to prevent further seeding around, but leaving the stem which I should be able to trace back to the offending bulb.

A. cernuum on the left, one of the lifted clumps on the right

This actually proved to be easier than I could have dreamt, for when I lifted the clumps I discovered that A. senescens – if that is what they are – as opposed to A. cernuum, actually do not remain as individual bulbs, but join together, forming woody, root-like, structures below the bulb.  The clumps were so tight knit that they took some prising apart, but I hope I have managed to remove all the offending A. cernuum bulbs, many of which had already started sprouting in readiness for next year.  This image shows the individual bulbs of A. cernuum on the left and a section of one of the lifted clumps on the right.

An added bonus of this operation is that I was able to identify, and remove, a number of triteleia which, in my book, fall in to the same category as A. cernuum!

My only problem, now, is that as they were such good clumps, and I have only replanted a small portion of each, I have about 20 pots available for sale.  So, if you see me with them, please ignore my comments about amateur gardeners with lots of the same plants for sale, and relieve me of some.  I promise that they are very well behaved, and lovely additions to the mid/late summer border.

Lockdown Gallery – week 28

September 28th to October 4th

This is the final week of our 2020 Lockdown Gallery. We hope you have enjoyed seeing what’s going on in other members’ gardens, even if you haven’t been able to visit them in person. Massive thanks to all those who contributed pictures or supported the Gallery by enjoying it!

Over the winter, we welcome pictures or articles about anything that you think will be of interest to your friends in WYHPS. Hopefully, we won’t be needing a Lockdown Gallery 2021, but if we do…

Weather: Much like last week – A dry warm start, turning cool, wet and windy from midweek. It’s autumn!

The Lockdown Gallery’s most regular contributor has been, without a doubt, Preston Harrison, who has sent pictures from his delightful garden every fortnight. For this last week, he is in contemplative mood – looking forward to the colours of autumn by looking back to October 2019

We haven’t seen Judith Ladley’s garden for a few weeks now, but clearly it does well in September, to judge from this fine contribution!

I’m delighted to welcome Brian Denison to the gallery – and I think he’s found a plant we haven’t seen before!

Sue Gray has been a regular contributor – I don’t know where she finds space for so many rare and interesting gems!

Throughout the season, HPS member Terry Benton has sent us pictures from his Wiltshire garden, providing an interesting comparison with the state of play in West Yorkshire. Here’s his end of term round up.

Well there’s not much in the Hackett garden that hasn’t already been dragged in front of the camera for Gallery duty, so here’s a few you’ve seen before, but in different combinations, in the hope of getting away with it….