UK Oak Open Days: June 15–17, 2024

The 2024 edition of the UK Oak Open Days focused on day visits to two parks in Berkshire, a county just west of London: Silwood Park and Windsor Great Park (mainly The Savill Gardens inside it). A third day saw us venture due south of London to two gardens near Haywards Heath in West Sussex. A total of 24 IOS members participated, mostly from UK, but including travelers from France, Belgium, and Uruguay.

We congregated on Saturday, June 15, at Silwood Park, the rural campus of Imperial College London, where Prof. Mick Crawley has single-handedly created a remarkable oak collection. Prof. Crawley is a renowned ecologist. His research has focused on the relationship between plants and their herbivores, and his studies have included the dynamics of oak acorns and the alien cynipid gall-forming species, Andricus queruscalicis. The infamous great storm of October 1987 provided an opportunity to acquire trees to relandscape a new area of the campus, and Mick managed to enlist the landscape design services of his multi-talented wife Greer (a theater designer by profession), so that the entirety of the scant budget for the project could be dedicated to acquiring interesting tree species, including many Quercus.

The day kicked off with a welcome from Mick, who shared his fascinating research on galls and acorns (you can watch some of it here). Then followed a tour of the oaks in the park. Though the trees are not labeled, Mick provided a very practical list of the oaks grouped by location. The collection is impressive both in the number of taxa and the size of the trees. Plant Heritage has recognized the oak collection as one of four National Collections of Quercus in the UK, with 230 taxa (200 species and 30 cultivars), while The Tree Register records 60 oaks at Silwood, including 10 County Champion trees, of which three are Britain and Ireland Champions. Highlights of the morning tour included some fine North American Red Oaks (Quercus hemisphaerica, Q. arkansana, Q. oglethorpensis, and the enigmatic and as yet unnamed taxon known as the Langtry oak—one of Silwood’s champion trees). Also noteworthy were several cultivars, including the attractive Q. ×hispanica selections ‘Wageningen’, ‘Fulhamensis’, and ‘Lucombeana’, as well as Q. ×turneri ‘Pseudoturneri’ and Q. robur ‘Filicifolia’. There was much discussion about the true identity of trees grown from acorns allegedly from a Q. faginea and a Q. canariensis in Silwood, both apparently crossed with Q. robur. Surely the most impressive specimen of the morning was a Q. castaneifolia, which has been strategically planted in space to allow it to spread its limbs, forming a fine canopy.

Following lunch Kevin Martin, Head of Trees at Royal Botanic Gardens, Kew, delivered a presentation outlining how Kew is preparing for the future and the anticipated changes in climate. Plans include sourcing Q. robur from West Asia to test whether it is better adapted to the conditions Kew is likely to face in the future.

Much of the afternoon tour centered on what Mick called Drive Field Arboretum, a large rectangular space, formerly a kitchen garden, where many oaks have been planted around the perimeter. Oaks from Europe, Asia, and North America co-habit this space, including Q. xalapensis, Q. pontica, Q. robur ‘Salicifolia’, and a champion Q. georgiana. Most interesting was a tree of unknown identity with very attractive new growth, dark red to purple against the light green mature foliage. Several theories were floated as to what it might be, the most plausible suggesting a hybrid between Q. myrtifolia and Q. nigra.¹

We saw some rare species planted next to a residence hall (Q. vacciniifolia, Q. durifolia, Q. semecarpifolia), and the tour culminated with a show-stopping Q. cerris ‘Argenteovariegata’, a mass of cream-lined, delicately lobed foliage.

The next day we were greeted at the entrance of The Savill Garden by John Anderson, Keeper of the Gardens at Windsor Great Park and our jovial host for the day. The Garden was one time the site of a plant nursery and was created in 1931 by Eric Savill, Deputy Surveyor of the Crown Lands at the Windsor Estate, who recognized the potential the area had due to a natural abundance of water. Thanks to this feature it was long known by the far-from-alluring name of The Bog Garden. Fortunately King George V, who had supported Savill’s initiative, renamed it in 1951 to honor its creator, and gave further evidence of his approval by knighting him in 1955.

The oaks at The Savill Garden also have a strong presence in The Tree Register, with 24 trees recorded, including four Britain and Ireland Champions. Several finely structured oaks make an imposing stand as soon as one enters the garden from the Visitor Centre: a Q. ‘Pondaim’ outshines the others with its huge obovate leaves (the taxon has now been changed to Pondaim Group and includes any product of the cross between Q. dentata and Q. pontica, according to The Oak Names Checklist), but other oaks vying for attention there include Q. coccinea, Q. nigra, Q. dentata, and Q. ithaburensis. Further on we encountered a Q. castaneifolia, where those unfamiliar with processionary moth (Thaumetopoea processionea) could get a good look at the ghastly procession of the caterpillars advancing up the trunk and learn of the risks of standing beneath them (aside from the damage to trees, the caterpillars are also a hazard to humans and animals, as contact with their hairs can cause itching skin rashes, eye irritations, and breathing difficulties). Other stops on our way included Q. laurina from Mexico, Q. stenophylloides from Taiwan, and the always spectacular Q. oxyodon.

John ably shepherded us at a steady pace so that we could cover quite some ground in the sprawling gardens and see all he meant to show us, despite a leisurely lunch extended by Father’s Day crush at Benugo, The Savill Garden's restaurant. The day closed with a trek to the Q. robur by Cumberland Lodge, one of the ancient oaks at Windsor Great Park, where author, scientist, and arboriculturist, Ted Green, MBE, shared his boundless knowledge of veteran oaks (a term he prefers to ancient oak: a veteran oak is an oak that shows ancient characteristics, regardless of its real age). Ted was born near Silwood on the edge of Windsor Great Park spent his childhood among the Park’s foresters before becoming a laboratory technician in plant pathology at Silwood Park and earning an honorary lectureship there.

On Monday our group, reduced in size, reconvened at Borde Hill, where we were hosted by IOS member Harry Baldwin, Head of Horticulture. Our morning tour took us to woodlands containing champion oaks (10 Britain and Ireland Champions are listed in The Tree Register, where 50 of Borde Hill’s oaks are recorded). Of particular interest were the unusual hybrids Q. ×ludoviciana (Q. pagoda × Q. phellos) and Q. ×morehus (Q. kelloggii × wislizeni). These are now massive trees in dense woodland, and getting a close look at them was at times adventurous. Another rare hybrid at Borde Hill is Q. ×auzendei (Q. coccifera × Q. ilex).

Harry’s tour of the garden and trees was superb and there is not sufficient space to go into detail here, but of special interest was a visit to the greenhouse, where Harry showed us seedlings from acorns of Q. alnifolia he collected in Cyprus, several bearing the silver leaf undersides typical of what some authors recognize as var. argentea.

After a sandwich lunch at The Gardener’s Retreat Café in Borde Hill, we scooted down the road to Wakehurst, a historic house and garden managed by Royal Botanic Gardens, Kew (it is described as Kew’s “wild botanic garden”). Jo Wenham, Curation Manager, met us at the door and promptly marched us back to the car park to see large specimens of Q. cerris and Q. petraea ‘Mespifilifolia’, an old (1822) cultivar with leaves resembling those of medlar (Mespilus germanica). Trees of this form are now known as Mespilifolia Group,

Once inside the wonders began with a superb Q. frainetto, then we closely scrutinized what looked very much like Q. serrata, though it is on the books as Q. glauca. A true and champion Q. glauca awaited further on, before we reached Wakehurst’s Quercus pièce de résistance, a large Q. trojana growing in front of the manor house, which at the time was sadly (though decoratively) covered up for repairs. We admired the floral diversity and views offered by the Coronation Meadow and ended our brief tour at the famous Millennium Seed Bank, browsing the exhibits on the ground floor, atop the underground collection of 2.4 billion seeds from around the world.

It is impossible to do justice to the gardens, landscapes, oaks, and other plants we crammed into three days in the UK, let alone the good company and interesting conversations. A more detailed report will be published in next year's Journal. Many thanks go to our hosts and presenters: Mick Crawley, Kevin Martin, John Anderson, Ted Green, Harry Baldwin, and Jo Wenham, and especially to IOS member James MacEwen, who was instrumental in setting up and organizing these Oak Open Days. Finally, a very special thank you to Ed Spurr and Amy Hall of Ilex Studio, who presented each Oak Open Day participant with an Acorn Vase, the Studio's signature creation. We are also pleased to welcome Ed and Amy as new Life Members of the IOS.

¹ Several weeks later, I was made aware that we had seen that hybrid at Arboretum des Pouyouleix during the French Oak Open Days. It turns out that Béatrice Chassé had in 2008 collected acorns from a tree in the citywide arboretum in Aiken, South Carolina that is a natural hybrid of Q. myrtifolia × Q. nigra, planted by Bob McCartney form wild-collected seed. The acorns she collected were distributed among several nurseries and collectors. Two trees from that source grow in Arboretum des Pouyouleix, and another grows in Jardín Botánico de Iturraran. It is quite plausible that the tree at Silwood Park is of the same origin, perhaps acquired from John Gammon of Birchfleet Nurseries, who would have received the acorns collected by Béatrice and distributed in the UK.

Photos © Roderick Cameron unless specified