WHF Trustee Chris Lane, who holds the national collection of prunus at his Witch Hazel nursery suggests some Prunus worth growing for their beautiful trunks alone, with flowers the icing on the cake (or cherry on top….) Reproduced with the kind permission of the RHS Plant Review (March 2024).
Upcoming events at White House Farm in June, July and August:
-a WHF Hydrangea serrata Study Day on Saturday June 8th (9 places still available), email whitehousefarmarb@gmail.com for programme details and to reserve a spot;
-A Garden Masterclass ‘summer colour’ tour on Weds July 10th (book via Garden Masterclass website here)
-An IDS Study Day on the important ‘asperae’ subsection of Hydrangea (aspera and involucrata) on Weds August 21st (book via the IDS website here)
Jack Aldridge, WHF Trustee and Horticulturalist at RHS Wisley, gave a Thursday Garden Chat for Garden Masterclass about his work on Oakwood at Wisley; other recent talks range from ‘Woody Plants that Should be Better Known and Grown’ for Plant Heritage, and an overview of Camellia sasanqua for the International Camellia Society.
Jack has recently played a key role, along with Rod White, who has an unofficial national collection of Camellia reticulata, in identifying and labelling the camellia collection at White House Farm (some 100+ cultivars and 40+ species) which will be a feature of the April 4th guided tour and discussion; as will Magnolias (200+, some 50+ years old, including 12 national champions), which Maurice Foster is speaking about at a Wespelaar IDS Magnolia Study Day in Belgium next month.
WHF is known for its use of Magnolias as canopy trees for underplanted camellias, rhododendrons and hydrangeas, along with other small trees of interest for their flower or foliage, from cornus, styrax, and corylopsis, to carpinus and euonymus, with clematis, wisteria and climbing roses joining in, wherever siting offers each plant its best combination of light and shade, space and protection. This tiered woody co-growing approach offers sequential colour but is also low maintenance, enabling colourful year-long effects achieved without a team of gardeners. As well as looking at the best spring-flowering plants, and others that deserve not to be rarities, these methods and more will be showcased discussed as design strategies at the April Garden Masterclass event – an informal guided tour designed to be directed by participants’ specific interests and questions.
Spring at WHF is dominated by the spectacle of magnolias on all sides, set off by evergreen camellias and rhododendrons below, with conifers as high backdrops. But WHF is also known for the range of other often overlooked genera in spring gardens, such as Meliodendron, Staphylea and Berberis, as well as the colourful spring foliage of birches, maples, and hornbeams. A few places are still available for the April 4th event: for more information click here.
Jack is working on Cornus for Trees and Shrubs Online (TSO) and has an article in this month’s The RHS Plant Review about Cornus hybrids – an issue which also has contributions by two other WHF Trustees, Chris Sanders (on an overlooked clematis) and Chris Lane (on dark-stemmed flowering cherries).
Jack will join Maurice Foster and horticulturalist and gardening lecturer Caroline Jackson in leading the first of a series of Garden Masterclasses at White House Farm on Thursday April 4th, informal tours designed to be led by participants’ interests and questions – observing not just the best or some rare selections but also some growing and planning lessons learned over the past 50 years.
Maurice Foster shares some observations on some of the newer wild Camellia species growing at White House Farm.
The four seminal species behind the largely nineteenth-century development of literally thousands of cultivars are of course C. japonica, C. sasanqua, C. reticulata and C. saluenensis. Their relative merits as species are already well known, and their influence on the vast treasurehouse of garden camellia hybrids immense. C. cuspidata has also been quite widely grown for many years. But over the last 20 years several other camellia species have been brought into cultivation; some of the most promising of these for garden-worthiness are among the 48 Camellia species we grow here at White House Farm.
The total number of designated camellia species varies markedly depending on which taxonomist you favour. In 1958 Robert Sealy at Kew described some 82 species from the material then available; by 1981, with many more species newly discovered in China, H. T. Chang recognised no less than 280. T. Ming brought this back to a more sensible 119 in 2000 – but this back and forth itself shows there is a challenge here, and scope for more work, both in the field and the laboratory.
Whichever taxonomic classification you follow, about 80% of species are to be found in China, with some new species recently discovered in Vietnam and elsewhere in E. Asia. Most of these Chinese species are found in the warmer temperate zones of the south and south west, with inland populations often at relatively low altitude, meaning that cold hardiness has been seen as the principal limiting factor for successful cultivation in the UK. The vigour of WHF’s collection seems to disprove this concern. Of course we have had a good run of milder winters, and some botanists believe members of Theaceae, such as Camellia, and the closely related Ternstroemia and Polyspora, for example, have cold hardy genes in their makeup. But it may be, too, that as for so many other genera, siting is crucial.
C. pitardii – the best of our 4 seedlingsC. tunganica, introduced by White House Farm
Here, finding the right spot for planting is the first priority, and the key to success in creating optimum conditions for survival and good growth. Most of our species camellias are located in the wood, or as underplanting in the mature garden, with wind protection from the bitter North Sea winter winds to the north and the east to which we are exposed being on a hogsback of some 500ft. But the same slope protects against spring radiation frosts, because colder air, being heavier than warm air, sinks – this katabatic wind means sheltered slopes avoid frost pockets. Rainfall at WHF averages about 30” a year: drainage is another benefit of slopes, and there’s a balance to be struck between top cover, root competition, and good light, although I have found that once established, C. species cope especially well with this. Light woodland is ideal, with part shade, some humidity, and plenty of moisture during growth.
Certainly, winter hardiness appears to be less of a concern after 20 years growing experience here. Not only have these newer Camellia species not succumbed to frost, but last year C. tunganica, introduced by White House Farm some 15 years ago, maintained fresh white flowers in abundance after a series of -7C nights: freshness of flower already the standout quality of this species, which drops before browning, essential in a white.
C. tunganica
Bearing in mind that all species vary from seed, some of these species can clearly hold their own with the best of the garden hybrids in flower and foliage. Of three large flowered red species, the spectacular red flowers of C. chekiangoleosa warrant inclusion in any collection – and although I am now pretty sure that some of my open pollinated seedlings are contaminated with C. japonica and are natural hybrids, my plants still show what is distinctive about the species: a tough, vigorous pyramid of bold glossy large elliptic leaves ( typically 16x5cm) studded with large cupped flowers of a vivid clear blood red, significantly larger than those of typical C. japonica. It outperforms the reds C. polyodonta and C. semiserrata, which have also survived multiple cold winters here (-7C).
C. chekianoleosa – this form likely a wild hybrid with C. japonica
A species that should certainly be more widely grown is C. trichocarpa. From SE Yunnan and SW Guizhou at altitudes up to 2300m it is moderately hardy: here three plants have been growing strongly without problem for 17 years. The 5-6cm white flowers appear in early spring and have a large central boss of bright yellow spreading stamens, presenting themselves beautifully on an upright shrub (reaching about 3m) among green 11 x 5cm wavy edged leaves with deeply impressed veins, and attractive cinnamon bark.
See Maurice’s 2019 RCM Bulletin article on C. trichocarpahere:
Ming reduced C. trichocarpa to a subspecies of C. henryana, but in cultivation the two are quite different. The flowers of the latter are much smaller, on a bush with a loose, spreading habit, and smaller, less impressively veined, acuminate 7x3cm lanceolate leaves more widely spaced on arching shoots. C. henryana is exceptional for its spring foliage: perhaps the best red young growth of all.
C. henryana – worth growing for its spring foliage display alone
Reddish coppery young growth is an attractive character of many species and is also a feature of C. yunnanensis, a species in turn often confused with C. henryana, as both flower from late October, and can continue over winter in milder weather into early spring. But C. yunnanensis flowers are relatively large, up to 8cm, produced both terminally and in the upper axils with the white petals reflexing to give still more prominence to the yolk-like shock of yellow stamens.
C. yunnanensis once mature (c. 10 years+) produces a good crop of conspicuous large fruits, like purple cheeked apples; as does C. tricocarpa, whose prominent apple-sized fruits, red where exposed to sun, are a valuable ornamental feature. I’ve found the seeds of this and most other camellia species also germinate, and the seedlings establish, very easily.
Also white-flowered but entirely different in character are C. forrestii, C. grijsii and C. brevistyla: all are small-flowered substantial shrubs, and all are proving to be hardy, achieving about 3m after 7-10 years. C. forrestii is particularly free flowering, terminally and in the leaf axils. The small flowers of some 3 – 4cms across are slightly cupped and slightly fragrant. Ovate petite leaves have a slight gloss on a bushy neat shrub. From Yunnan and found up to 2500m, it has been perfectly at home here and our two plants are fringed by dozens of self sown seedlings.
C. pitardii, with a wide distribution in China, is perhaps my favourite, variable in habit and in flower, with colour ranging from rich pink to white. In a good form flowers are of high quality, some specimens a clear shell pink, with little of the more typical vinous underlay. I have three different collections, all growing well after a decade; the best has an open habit and clustered flower buds, both terminal and axillary, with up to twelve buds on less than a foot of stem. The elegant open funnel shaped flowers are up to 8cm in diameter and open in succession over a long period from February onwards. It is an excellent plant often confused with C. saluenensis, parent of the great C. x williamsii race.
The Taiwanese species C. transnokoensis is now well known and frequently planted. It has turned out to be surprisingly hardy, and its dense bushy habit, small leaves and abundance of small flowers in spring make a great display. We grow 3 or 4 forms, the best with dark pink buds, the colour retained on the back of the outermost petals when open, particularly attractive. It is an excellent candidate for a small garden, or a specimen plant in a pot.
Many other new Camellia species are thriving in Cornwall – these notes offer a mere glimpse into a future full of exciting potential, and suggest what is already possible in Kent. This looks likely to be a continuously expanding new range of plants which are beginning to prove their value in gardens, and for hybridising, too. They certainly offer beauty and interest in a far more demanding range of garden conditions than their native origins might seem to allow.
References: Collected Species of the genus Camellia. An illustrated outline. By Gao Jiyin, Clifford R. Parks, Du Yueqiang.
See Maurice’s 2017 RCM Yearbook article on Camellia species here.
There will be an IDS Study Day on the genus Camellia on Saturday March 30th at White House Farm: for more information click here.
There will also be a Garden Masterclass guided tour of White House Farm Camellias and Magnolias on April 4th: for more information click here.
By WHFAF Trustee Christopher Sanders VMH. This article was originally published in December 2023 by the RHS Plant Review. Reproduced by kind permission of the RHS.
Erwan Le Bec, a French horticultural student at INH school (Agrocampus Ouest Angers) writes about his recent visit to us as an intern. He left us with extraordinary photographs and research notes about our collections.
Since I was a child I’ve had a particular interest in the world of plants.
It started with my grandfather’s vegetable garden, then moved to ornamental plants, and especially woody plants, whether trees or shrubs, because to me they seemed incredible living creatures, able to survive against all the difficulties of our world. This passion developed over the years and I decided to take advantage of my studies in landscape design to deepen my knowledge of botany. I began in 2019 with an internship at the Roscoff botanical garden, then continued with an internship at the Aoba nursery, run by Cédric Basset and Manon Rivière, and, last year, had a unique experience at Wespelaar arboretum with Christophe Crock and Koen Camelbeke. This world of trees and shrubs is now for me both a refuge and an idyllic setting for a future professional life.
A selfie with Carpinus fangiana
For several years I’d been hoping to be able to have some experience in gardens in England, to improve my English and my knowledge of plants at the same time. Last summer, during a talk in Herkenrode with Philippe de Spoelberch, we spoke about the garden at White House Farm and its wonderful Hydrangea collection. Having worked on the Hydrangea collection at Wespelaar arboretum, WHF seemed a good choice for my next internship destination. After few emails, I agreed with Maurice Foster on a 3-week internship in August 2023. As soon as I arrived, I felt right at home at White House Farm, with a nice welcome from Clare, her children and Maurice. The atmosphere was incredible: a house in the middle of a treasure trove of plants from so many different horizons. The Hydrangea aspera had just begun to bloom and were shining in all their splendor, like images I’d seen in books about the flora of China.
From the very first evening, Maurice welcomed me with open arms into his world, giving me access to his knowledge and some interesting books: it was the beginning of an incredible experience, three weeks of pure happiness. During these weeks I inventoried with Maurice some zones in the garden, and some genera like Carpinus, Sorbus, Corylus and Euonymus. Thanks to this work, I discovered my favourite plant of the garden: the Magnolia wilsonii x Magnolia globosa seedling from one of his collections that he has nicknamed ‘Parachute’ because of its very big white flower.
White House Farm Magnolia seedling ‘Parachute’, 17cm across
Any activity with Maurice at White House Farm is interesting and instructive, because at WHF each plant has its own story, so every day he took me with him to the different regions of his travels. For example, he discovered Carpinus fangiana in Yunnan in 1998 with some American botanists – the tree had no fruits, and they thought that the foliage looked fagaceous, and was probably an oak. But Maurice kept on searching, and finally spotted a the very characteristic single fruit of Carpinus fangiana in some taller branches. I also helped the arboretum team for one day a week, pruning, tree-felling, and weeding, which was a great way to learn about plant collections in a different way, as something constantly changing. And every week Maurice took me to different famous gardens like Wisley, Nymans and Hilliers to meet different plant specialists, such as Chris Sanders, Chris Lane, Rod White and Jack Aldridge. It was a great pleasure to talk to them, each one a specialist in his own areas.
Rod White’s private garden
This unique and comprehensive experience was very encouraging; it helped me feel I belong in this world of enthusiasts. So I’m finishing my last year of study in landscape design by specialising in urban green spaces, with a 6-month work experience in February 2024 to conclude my course, which I hope to do in a garden or arboretum. My sincere thanks to Maurice and Clare for their welcome, and to Philippe de Spoelberch for this recommendation.
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It’s well known that some Mexican species and their hybrids such as P. maculatus, P. mexicanus and P. ‘Belle Etoile’ possess a gene for the colour pink, but this is manifested as a more or less basal blotch on the inner surface of the petals, resulting in a central ring of pink or purplish-pink in the heart of the flower. However, those present at the recent Philadelphus Study Day at White House Farm were intrigued when shown a young shrub recently planted out in the Wood, which was clearly exhibiting pink-flushed flower buds and whose petals had faint pink streaks on their exterior.
Maurice told us that he had been given this as a cutting under the name of Philadelphus aff. delavayi “pink form” during an RHS Woody Plant Committee visit to Bodnant in North Wales a few years ago. The name seems somewhat doubtful, given that P. delavayi is an early-flowering species; other examples of P. delavayi in the collection (a fine melanocalyx B & L collection and the Nymans form, for example) had mostly finished flowering by the study day (17th June), although a longer-lasting P. delavayi flavescens was still going strong into July. It reminded me that I had once seen something similar many years ago on a visit to Highdown, the famous chalk garden near Worthing, Sussex, created by Sir Frederick and Lady Stern. It bore no label, but at the time I attributed it to P. tomentosus.
Philadelphus tomentosus? A pink form of Philadelphus photographed by the author at Highdown
Fortunately, I took photographs of it because on a more recent visit I found that the border where I last saw it had become a dense, overgrown thicket and there was no sign of the pink philadelphus. Hopefully it is still there, but the whole border is in desperate need of drastic pruning in order to give it a chance to recover. In the meantime, fellow trustee Jack Aldridge found in the Wisley library the following brief reference in EXTRACTS from the Proceedings of The Royal Horticultural Society, Vol. LXXXI, 1956, Part Two:
Referred to Scientific Committee and to be seen at a future meeting:
Philadelphus L. & S. 17408 (pink form) exhibited by Sir Frederick Stern O.B.E., M.C., Highdown, Goring-by-Sea, Sussex.
This must be the same thing I saw at Highdown. Further research revealed that L. & S. 17408 was collected by Frank Ludlow in Gyasa Dzong, NW Bhutan, on Oct 3rd 1949. Frank Ludlow and George Sherriff (L. & S.) collected mainly in Bhutan and SE Tibet, and P. tomentosus is native to the Himalaya. More details have been requested on the precise origins of both this and the Bodnant plant, and I’ll report back here as more information comes in.
Another picture (by Jack Aldridge) of White House Farm’s Bodnant ‘pink form’: encouragingly pink in bud.
Might there be a connection between the Highdown and Bodnant plants? Back in the 1950s at the regular RHS fortnightly shows at Vincent Square, there would have been much keen but friendly competition involving many of the great gardeners of the time, including Sir Frederick Stern from Highdown and Lord Aberconway from Bodnant. Plants and/or cuttings were likely freely exchanged afterwards, so the Highdown philadelphus could well have found its way to Bodnant.
It is, then, not inconceivable that the pink genes of the Mexican plants could be married to species like these from the Himalaya, and maybe after a couple of generations we might see a really pink philadelphus.
As a result of the successful Philadelphus study day held at WHF on Saturday 17th June, two rare Lemoine Philadelphus cultivars believed to have been lost to cultivation have come to light.
Philadelphus ‘Oeil de Pourpre’ (Purpureomaculatus Group)
Trustee Jack Aldridge, who is based at Wisley, brought a handsome specimen from that garden labeled ‘Oeil de Pourpre’. At first, both Maurice and myself, who had both grown and lost this cultivar in the past, and remembered it as a rather weak plant of poor constitution, were rather doubtful about its identity. However, on returning home, I dug out some images taken many years ago when I grew a specimen obtained from the National Collection of Philadelphus at Leeds, and I’m now convinced that the Wisley plant is indeed correctly named. In the attached image its chief characteristics of a deep purplish basal blotch (the deepest colour of any Philadelphus) and the distinctive cup-shaped blooms can clearly be seen.
‘Oeil de Pourpre’ was raised by the famous French Nursery of Victor Lemoine et Fils and introduced in 1910.
Philadelphus ‘Oeil de Pourpre’ Photo: Chris Sanders
At the study day, there was some discussion about two other Lemoine cultivars, namely ‘Bicolore’ and ‘Purureomaculatus’, neither of which had been seen in cultivation for some time. I later recalled that a plant from Leeds which had been distributed as ‘Bicolore’ had been misidentified and was really ‘Purpureomaculatus’, but, like ‘Oeil de Pourpre’ seemed to have become very rare and no longer offered for sale. Arguably, this is the most attractive of the group with widely expanded medium-sized flowers having a good purple blotch at the base of each petal.
Philadelphus ‘Purpureomaculatus’ (Crathes)
A couple of days after the event, the indefatigable Jack alerted me to a small Shropshire nursery (Harley Nursery, near Much Wenlock) who were offering ‘Bicolore’ for sale via their website. Photographs accompanying the text left no doubt in my opinion that this was clearly ‘Purpureomaculatus’. A visit to the nursery on the following day resulted in the purchase of five lusty plants for distribution to interested parties. Also, interestingly, the nursery owner confirmed that he had obtained his original stock from the (now defunct) National Collection at Pershore College in Worcestershire. As a former student at this college who was very familiar with the collection in its heyday, I was aware that much of the Pershore collection had been obtained from guess where – Leeds!
‘Purpureomaculatus’ was raised by Lemoine and introduced in 1902.
The above two cultivars are really important discoveries and the intention is to propagate them as soon as possible for wider distribution. Now it just remains to try and track down the real ‘Bicolore’.
On Saturday April 8th students and faculty from Wisley, Great Dixter and Kew gathered round a table of vases of magnolias in current bloom, selected from the WHF collection of around 250 species and cultivars from Magnolia, Michelia and Mangleitia. These students were joined by WHF Friends and Volunteers from a variety of backgrounds, from landscape architects to directors of other well-known gardens nearby. The table was set on the main lawn, ringed everywhere by magnolias up to 30-40 ft in the garden landscape, conspicuous against a dark backdrop of conifers. Twelve of these are Tree Register (TROBI) National Champions (eg Apollo, Arnold Dance, Sundew, Sweetheart, Pickard’s Snow Queen etc).
M. ‘Red Lion’, one of Oz Blumhardt’s sister seedlings to ‘Star Wars’ – a national champion at WHFNarisa Kempster, horticulturalist at RHS WisleyElouise Curtis (Student at RHS Wisley with WHF Truystee Chris Sanders VMH, and ‘Honey Tulip’ (a Jury)Great Dixter studentsCaroline Jackson, Horticultural LecturerPhotographic comparison of one of four WHF meliodrendron selections also in flower, and a wild collected ArizelumThe ‘classic’ denudata, purchased from Marchant’s nursery 52 years ago. Peerless for its form and beauty. M. stellata ‘Mags Pirouette’ with Gresham’s Fortyniner in the foreground and Llanhydrock in the background‘Black Tulip’ stands out in vases for its colour and form: a ‘classic’ from Mark Jury in New Zealand
Another table provided continuous cups of tea and coffee, and someone brought two tins of chocolate crispies, essential requirements to keep the show on the road.
A few last flowers of the earlies – sargentiana var robusta, campbellii , campbellii var mollicomata and dawsoniana- were still available for the vases, plus some examples of their hybrids and forms, such as the Raffilii Group, Premier Cru, sargentiana var robusta ‘Blood Moon’, dawsoniana ‘Clarke’ and ‘Valley Splendour’.
Vases picked that morning showing the main horticultural divsisions, with M. ‘Iolanthe’ and ‘Dawn’ in the background. The Nothogfagus (centre) coming in to leaf marks the spring timing.
Maurice arranged 8 vases divided into main horticultural subdivisions of most practical use to horticulturalists and garden designers, and containing examples of representative specimens:
1 The early Asiatic trees (campbelli, dawsoniana, sargentiana var robusta – see above)
2 Stellata, loebneri and denudata (see above)
3 Sprengeri (Copeland Court, Lanhydrock, Claret Cup etc)
7 Michelia/Mangletia (only Michelia doltsopa, and Michelia yunnanensis in flower)
8 Yellows (only Petit Chicon and Honey Tulip beginning to flower)
‘Honey Tulip’, open on April 8th: a truly precocious yellow of fine globular shape, the colour of solid honey
Vases of M. stellata , like the best pink form ‘Jane Platt’ and pale pink ‘Dawn’ were featured with cultivars of the tough, weather-resistant M. kobus x stellata M. x loebneri, such as the favourite fragrant Mag’s Pirouette, free flowering long-lasting ‘Merrill’ and the larger flowered ‘Donna’.
Is this Peter Smither’s ’32 tepals FV’ or Jane Platt? Are they different?
Two additional vases could be added – the summer flowering Oyamas and the evergreen grandifloras that do not begin flowering until May and were therefore not represented; but our evergreen michelia Doltsopa, over forty feet, gave us a fresh first flower.
Michelia Doltsopa
There was plenty of discussion of subjects like growth rates, weather resistance, length of flowering time and notably the questionable value to horticulturalists of sinking Michelia and Mangleitia into Magnolia when there are morphological characters of significance to gardeners that clearly distinguish them. There was a consensus that this was unhelpful as there is useful horticultural information and history contained in a name, and the value of this is sharply reduced by placing these two genera into the generality of the wider genus of Magnolia. For example, what value is there now in calling Mangletia decidua (significantly named as the only deciduous plant in an evergreen section) Magnolia decidua, when so many other magnolias are deciduous? The power and point of the name is hollowed out…..
A Keith Rushforth collection of campbellii alba, the ‘classic’ white campbellii that really should be the type species if William Griffith (1810-45) hadn’t died prematurely and his diaries taken so long to be published. Photo: Jack Aldridge
After lunch, the group toured the arboretum where distractions like Meliodendron xylocarpum, Corylopsis and Stachyurus and large leaf rhododendrons were seen, along with more magnolias – notably a superb M. campbellii alba from the Himalaya flowering for only the second year with 8 flowers; and the final flowers on ‘Premier Cru’, a WHF seedling.
Extraordinarily delicious home-baked cake generously provided by Wisley staffer Narisa Kempster rounded off the day, with the plant of the day over tea winning most votes (4 out of 24) not a magnolia, but the meliodendrons then in early flower, especially the Hillier form and MF’s own collection, one freely flowering for the first time this year as a 11 year year-old tree, a nice pink. A forty-foot specimen Gresham Magnolia ‘Manchu Fan’ and M. loebneri ‘Mags Pirouette’ were also featured in the vote.
Text: Maurice and Clare Foster. Photographs by Owen Hayman and Clare Foster.
WHF held a propagation skills workshop on a cold weekday in early March 2023. Talks were given by Chris Lane on grafting, Peter Shotter on seed germination, Maurice Foster on cuttings, and Nadeesha Bandara shared details of the research project she’s part of at Nottingham University about the influence of hormones on rooting. We had eighteen students from Kew and Great Dixter plus Rod White from the RHS Woody plant Committee and Jack Aldridge from Wisley, so were crammed cosily in the conservatory on a snowy day with a continuous supply of tea and coffee, followed by a muddy tour of the arboretum when the skies cleared.
Maurice introduced the day by saying that the next generation of horticulturalists carry a great responsibility precisely as propagators, because without ‘looking after, growing on, sharing all the stuff that’s been collected’ the wonderful plants we’ve got now that are not being produced commercially will disappear. He said ‘botanists used to be sniffy about what they call ex situ conservation but have come to recognise this is increasingly important as large areas of wild populations are eradicated…so skilled propagators now and in the future will bear a huge responsibility in conservation’ – not just in enlarging the range of good garden plants available to designers and gardeners.
Chris Lane has done hundreds of thousands of grafts in the past five decades, the prerequisite of being able to create and maintain five national collections at his Witch Hazel nursery in Kent – Prunus (flowering cherries), Hamamelis, Wisteria, Parrotia and Amelanchier. After stressing the importance of maintaining your own razor sharp knives from his talk I learned more about the logic behind the differences between the two main times of grafting, winter and summer. In winter (usually whip grafts – a diagonal cut that binds the end cut of the rootstock with end cut of the scion, aligning and matching the circling edges of the cambium – there will be minimal activity in the scion and rootstock, so pot conditions need to be dry and very well-aired, and low temperatures can be taken advantage of to that end – what Chris Lane calls ‘cold callousing’. With summer grafts, usually side veneer grafts – where only one side of the root stock is cut, peeling back to a short flap at the base where sharply-tapered young scion material is inserted – both scion and rootstock are in the midst of vigorous growth, so moisture is less of a problem, but leaves need clipping by at least half of their area to minimise transpiration. So summer grafts will do well in a fogging unit, or under polythene; whereas winter grafts need to be kept dry in the pot while dormant.
Chris Lane discussing low tech hot pipe grafting at home
A side veneer graft
Hot pipe grafting over the winter enables warmth to applied confined to just the union to encourage callousing while avoiding rot. Chris showed students how to make a home-made version of this technique. For more details of this and other grafting tips Chris mentioned, there’s a good comprehensive print introduction to grafting by Brian Humphrey, The Bench Grafter’s Handbook, by CRC Press (2019).
Peter Shotter on soils for optimal seed germination
Peter Shotter said the key to sowing seeds of woody plants was the composition of the compost – it should be low in nutrient and very free draining. He mixes his own sterile medium with as much as 50% grit, and 50% peat or peat substitute. He also makes his own bespoke leaf moulds. Perlite is a commonly-used alternative to grit, but Peter has found it associated with rot in lilies and other bulb seeds, or other seeds that need a long time to germinate. A heated propagator isn’t necessary if more patience with a cold frame is an option – and artificial warmth can backfire for slow-to-germinate species by encouraging rot and disease, especially in the case of large woody plant seeds such as camellia, peony, oak and magnolia etc. Chris Lane pointed out the need now to be able to grow your own understocks from seed because of reduced commercial availability, and Maurice said he’s seen the same sorbus seeds take from 1-7 years to germinate, which is an evolutionary survival mechanism – if the same seed treated in the same way germinates at different times, if the first to grow dies, more are on their way. For this reason he sometimes uses petri dishes in the fridge to be able to lift seeds as they germinate without disturbing the others. Peter discussed growing-on, and his potting on compost mixture for the seed of difficult bulbs, such as lilies – a third leaf mould, a third grit, and a third commercial ericaceous compost.
Moving to cuttings, Maurice emphasised three things – the importance of juvenility, of the timing when the cutting is taken (a function of the state of the wood, not the calendar), and aftercare. Cuttings have to be taken early enough for the rooted plant to retain enough carbohydrate to survive their first dormant winter. With woody plants such as birches and maples it is essential to keep them dry and not to transplant them until they start growing the following spring. The idea is to keep them in a state of suspension or stasis. During this period if moisture is not controlled they will rot off, so the sterile compost needs good aerating grit to ensure a supply of oxygen at the root: dryness while dormant is key. He added that 80% of losses in planting out woody plants from pots in the garden is due to planting too deep – and it’s the same with cuttings when you first pot them on: allow the root shoulders to be just visible, perhaps adding some grit on top – and again, avoid nutrient-rich commercial composts, as well as potting on into too big a pot. Keeping constant temperature during sunny periods is important, so misting and shading will be necessary, but without restricting too much light for photosynthesis – it’s a balance.
A bark sliver can encourage and enable monitoring of callusing
Then Nadeesha Bandara from the University of Nottingham shared details of an ongoing research project on the effects of hormones on rooting.
Our next Study Day will be on Magnolias, on Saturday April 8th, with a few places remaining. The early Asiatics – campbelliis, sargentianas and dawsonianas will be mostly over, but there will be plenty of others to see – and the soulangeanas, loebneris etc should be at their peak. To apply, or for more information about our 250+ collection of Magnolia cultivars and species, contact Clare Foster at whitehousefarmarb@gmail.com.
Looking at Betula utilis ‘Chris Lane’ with Chris Lane on March 9th, 2023
by Clare Foster, Chair of the WHF Arboretum Foundation
White House Farm Garden and Arboretum 