Boasting 12,000 different types of hardy plants, trees and shrubs, 14 National Tree Collections, and the largest number of Champion trees recorded in any garden within the UK, the Sir Harold Hillier Gardens and Arboretum isn’t to be missed.
AS unlikely as it seems in early July, visitors to the Sir Harold Hillier Gardens and Arboretum (SHHG) near Romsey, Hampshire, are enjoying a rain-free day. From the bus stop to the entrance pavilion, abundant car park landscaping lends a feeling of already being in an arboretum. An avenue of deciduous dawn redwoods, planted 22 years ago, has been growing for moments like these, when sunlight turns swathes of linear branchlets a shimmering yellow-green. Ruffling their fern-like foliage reveals them to be feathery soft.
Entry to the garden is via the courtyard, abuzz with visitors to-ing and fro-ing between the courtyard café and visitor centre exhibition space, the education centre and the gift shop. A bridge over a water feature leads into and out of the gardens. Beside the bridge, a blackboard highlights today’s ‘Plants of Interest’. Beside the blackboard, head gardener Fran Clifton and head arborist Matthew Strand engage in conversation with visitors who are happy to be able to converse with the professionals.
Talking with the managers – no matter how long or short the conversation – always enhances a visitor experience. Today, it fleshes out ‘A Walk in the Woods’, one of an occasional series of features, in an English Heritage Grade II listed Garden and Arboretum with 12,000 different types of hardy plants, trees and shrubs (with over 40,000 individual plants), 14 National Tree Collections and the largest number of Champion trees recorded in any garden within the UK.
The seeds of the 72-hectare SHHG were first sown in 1953, when plant collector and third-generation nurseryman Sir Harold Hillier bought Jermyn’s House and grounds, using some of the land for planting trees to be sold with mature rootballs through the Hillier Garden Centre (now a separate entity). Hardy plantings covering the steep valley sides, such as those in Himalayan Valley, being more complicated to harvest, now form the backbone of this 70-year-old arboretum.
In 1977, Hillier placed the house and grounds into a charitable trust to be run by trustees Hampshire County Council under the remit of ‘Horticulture, Conservation, Education and Recreation’. Today, with Royal patronage of Queen Camilla, SHHG welcomes 250,000 visitors a year, of which 25,000 are paying members.
Across the bridge, a pathway wide enough to accommodate the hospitality buggy (and electric mobility vehicles for hire) leads us towards the National Collections Glade, on the way passing a ‘Current Plant of Interest’, the burgundy flowered smokebush (Cotinus coggygria ‘Candy Floss’), a multi-stemmed Eucalyptus dalrympleana and a Eucalyptus brookeriana.
Planted in 1995, the National Collection Glade contains a well-appointed bench. The view towards Three Acre Paddock is abundant with canopies: the dark-red Acer platanoides ‘Crimson King’; a swamp cypress (Taxodium); a tupelo (Nyssa); bird’s-nest bamboo; the orange top of snow gum (Eucalyptus pauciflora) just coming into foliage; and a tall and bushy champion grey poplar (Populus x canescens ‘Macrophylla’), SHHG’s tallest tree at 32 metres.
Plant Heritage logs national collections nationwide. Fran explains: “To gain national collection status, you must have 80 per cent of the plants offered in the ‘Plant Finder’ catalogue. Ours include some of Sir Harold’s favourite trees – oaks – with 500+ different species and cultivars. Some are so rare they are not even listed. We also have the largest number of big specimens. Seeing the relationship between size and space is quite important, and then you have to manage them.”
Management is courtesy of an 18-strong horticulture team and an arboriculture team that employs two full-time arborists. Both departments offer apprenticeships. Since last year, the Royal Forestry Society has funded SHHG’s arboriculture student. Fran says: “Students are taught not to see trees in isolation.” Matthew gives an example: “We [the departments] blend our teaching. Trees are plants and anyone can formatively prune a small tree with a pruning saw, rather than call in the arb team.”
Fran began her career as an apprentice horticulturalist near Stuttgart in Germany. She moved to Switzerland to work at a nursery specialising in herbaceous trees and shrubs, before travelling through Europe, arriving in England in 1993. Within a year she had gained an internship at SHHG. Following a spell working abroad, she later returned to SHHG, working her way up to head gardener.
Matthew joined SHHG as head arborist two years ago. He brings with him 25 years of experience, having worked in the private and public sectors as lead climber, tree officer for a local authority, arboriculture manager and consultant.
Both teams are based in a former farmyard behind the pinetum. Barn buildings house a mess room and storage for machinery: four tractors and trailers; an ATV utility vehicle; a woodchipper; horticultural hand tools (electric) EGO hedgecutters, blowers, brushes, and arboricultural hand tools, (electric) Stihl blowers, polesaws and small ground saws). At the far end of the yard, a 200 m³ greenhouse is under construction and will also contain a dedicated propagation workspace for (among other things) grafting tricky species like oak, acers and prunus.
Garden arisings decompose in 80 m³ compost bays alongside woodchip used as mulch or for laying on paths. Large logs are often used in log walls or to provide stag beetle habitat. Smaller logs and brash arisings form dead hedges around the grounds. Bindweed leaves the site in normal waste collections, while Japanese knotweed is incinerated.
From the shade of the boathouse, visitors look across the pond to a small-kneed swamp cypress (Taxodium distichum), “one of the Garden’s most photographed trees,” says Matthew. “Our corkscrew willow ‘Contorta’ is ailing for no obvious reason. It was looking a little thin last year. Sometimes plants just do not do very well. It could be that it is on a small island surrounded by water, or climatic conditions: the heatwave two years ago.”
It may be too soon to raise the issue of climate chaos, but when asked, these managers do not shy away. There was a time when night-time temperatures of -10C or -6C for four or five days proved not all shrubs to be hardy, like Acacia (Australia) and Hebe (New Zealand). However, the Fitzroya cupressoides (Patagonia) survived well. Recent summer droughts have revealed some species tolerance. “Pears did well and can equally cope with wet,” says Fran. Matthew adds:
“Some of the oaks and a group of beech also did well. Conifers prefer drier soils, although we noted Pinus strobus and Metasequoia glyptostroboides seem able to cope with wet.”
Storms – more frequent and more severe – and wet winters affect the tree stock most. “Land is waterlogged for months rather than weeks. Losing a wider variety of species in those areas has affected our arb management.” Fran gives an example: “2022’s Storm Eunice, followed by Storm Franklin, severely damaged 84 trees across the Gardens, with some needing removal.” Matthew notes: “Deciduous assets suffered marginally less.”
Fran believes that the climate is warming. If there is a positive to be found, it is the chance to grow more diverse species. She says: “Mexican evergreen oaks would not have survived before.
Given that the garden and arboretum is a living library, a living seed bank, exploring a diversity of species possibilities, we might find some that hold the future ticket.”
Adapting management regimes has helped. Until five years ago, mowing the 6-ha wildflower meadow short every two weeks left the ground hard and cracked in summer and waterlogged in winter. “We stopped mowing, cutting in access paths for visitors and for the education department’s sweep-netting (from which children identify the bugs). Changing the mowing regime, the sward is capturing the water and the water table has balanced out.”
On a ridge above the pond, an abundant lime crown screens the stem of a very bleached and very straight (P1960) snow gum (Eucalyptus pauciflora) stem 25 metres high, with a DBH approximate to a two-person arms-length hug. Nearing the end of peeling season (late spring to July), the red and green bark of a champion Tasmanian yellow gum (Eucalyptus johnstonii) is muted. Youthful camellia plantings are protected from muntjac deer with recycled plastic cages.
SHHG benefits from 200 volunteers who work a day a week throughout the year. One arboriculture volunteer spends their time measuring Champion trees (TROBI), 611 at last count. The ‘Young Treecare Team’ removes cages, adjusts stakes and guides leaders back towards their bamboo canes.
We access ‘Woods of the World’ via a track mown through longer grass, under utility powerlines and between thinned Douglas fir and western hemlock. Until 2003, this 8-ha (P1940) forestry plantation was managed by the FC. SHHG acquired the site in a land-swap with Hillier Nursery and applied for an 80 per cent felling licence. Fran says: “The FC felled the trees and took the timber. We made the decision not to mulch – it destroys all life forms in the soil – and moved the brash into dead hedges.”
The firs provide dappled shade for young woodland plantings from three geographic regions: Japan; Continental Europe; Northern America. “We almost have continuous-cover forestry, with our young plantings growing up in this nurturing woodland habitat.” A nearby example is a rare Magnolia tamaulipana (Mexico). In the UK, Magnolia is best known as an urban garden tree. This whip reveals its true nature as a woodland species, putting on growth of over 7-feet since 2020.
A veteran tree specialist (VetCert qualified at a consulting level), Matthew says that SHHG has older oaks, a 500-year-old boundary yew and a veteran sweet chestnut maintained beside a well-used pathway as a giant pollard. Fran says: “A branch dropped one summer and it became dangerous. We shave off the branches every two to three years.” Matthew says: “Retaining the hollow stem is important as it provides a niche habitat for invertebrates, fungi, birds and mammals. As long as the cambial layer keeps producing new sapwood and bark each year, the hollow structure is still viable in risk-management terms.”
Although subject to a vermin-control policy, squirrels have been at the hazelnuts, leaving empty shells on a stump adjacent to the (double-fenced) one-acre Saddleback pig enclosure. Every year (since 2008), the pigs arrive in March and move on in October. A visitor attraction in their own right, we find them on a break from scrub and bramble clearance, taking a siesta beneath a spray of indigestible bracken. Sycamore and birch are regenerating well.
Moving downhill towards Himalayan Valley, a north Indian poplar grows beside a crenulated (castle) viewpoint as part of a conservation programme. Fran says: “We have three of this rare Populus purdomii. It is on the IUCN Red List, endangered due to overgrazing, overpopulation, industrialisation, and overuse of the timber. This story applies equally to us in England, with Dutch elm. Every plant has a story to tell. For example, you can eat the strawberry-like fruit of the flowering dogwood (Cornus), but it is not particularly delicious. Bladdernut (Staphylea) seed is used as a substitute for coffee or nuts. Conveying these stories is how people remember things.”
The approach to Jermyn’s House (now the garden restaurant) contains the Dwarf Conifer Collection. Growing alongside them is a foot-high umbrella pine (Sciadopitys verticillata ‘Grune Welle’) that has not yet reached full height. Following 60 years of growth, a champion Serbian spruce (Picea omorika) doesn’t appear dwarf-like anymore.
A substantial dawn redwood (Metasequoia glyptostroboides) grows next to the far side of the house. This Metasequoia is a second-generation ‘rescue’, grown from a seed collected in 1941 by the Morton Arboretum expedition to China. “Sir Harold corresponded with people all over the world to make sure he got seed.”
In 1964, Hillier laid out Centenary Border in what was then just a field. Refreshed in 2010, at 250 metres it is one of the longest double mixed borders in the UK. Golden Gleditsia, a (now) champion Abies chengii, a champion sequoia ‘Cantab’, a columnar acer ‘Sentinel’ and a square design feature of four hornbeams are some of the tree species providing a backdrop for vibrant herbaceous and bedding plantings. Matthew says: “Even I can appreciate these pretty things on the floor.”
Centenary Border ends at a wall of green. Species here include (among others) two columnar fastigiate oaks (Quercus fastigiata), one of which is dedicated to the late Queen Mother, who accepted the arboretum on behalf of Hampshire County Council in 1978. Of two small black pines (Pinus nigra ‘Moseri’) planted by Sir Harold Hillier and his then head gardener, Fran says: “The rumour is that that the pine planted by the head gardener is bigger. Whether true or not, I don’t know.”
Each year, SHHG draws up a planting list of 250 shrubs and trees, often based on what is in the propagation nursery. “We grow between 5,000 and 10,000 plants a year, often regenerating or regrowing (grafting in-house) trees and shrubs from material collected on site, because much of what we plant you cannot find in the trade. Sir Harold accepted all plants sent to him, so we are not restricted in our choices to certain regions or eras and we do grow from seeds sent in by collectors or make purchases for specific projects.”
Last January, as part of a European-wide conservation planting initiative (with Botanical Garden Sydney), SHHG were invited to host a new set of Wollemi pine plantings. Matthew explains: “The batch released 20 years ago were not very diverse, suffering with disease, fire and other climatic issues. This time, they have taken genomes from all trees in the valley (outside Sydney) and diversified. We have planted out six. They differ from every other group to ensure resilience, an insurance policy should things go wrong.”
Returning towards the courtyard, the weeping tassels of a white oak (Quercus longispica), collected from western China by plantsman, author and broadcaster Roy Lancaster, prompt Fran to say that there are two genera of oak, Quercus and Lithocarpus. “The way to distinguish them taxonomically is that the genus Quercus has weeping flowers, while Lithocarpus has upright flowers.” With nearly 300 evergreen species, relatively few Lithocarpus have been introduced into cultivation. SHHG have nine in their National Collection.
Matthew mentions that a recent local outbreak of OPM prompted the FC to ask SHHG to host pheromone traps, helping to identify which way and how far the moths are travelling. “I have heard (from Kew and others) that some of the evergreen species of oak are less prone to them. Looking at how they have been managed in London and Europe, infestations appear quite localised and unlikely to completely defoliate trees. We will find out in due course. If we do get them, the biggest issue is the public health risk.”
Now free of school children eating lunch – on some days SHHG accommodates up to four school groups, hosting 15,000 individual educational visits a year – the grassy field behind the education centre is being prepared for two music concerts being held this weekend. Tickets sold out in February. To protect the root zone of two parkland oaks, the arb team has spread a large oval of brown mulch around both stems. Concert-goers are unlikely to set up picnic tables on bare soil.
The courtyard hosts a solitary golden rain tree (Koelreuteria paniculata), selected for its tolerance to heat and drought. Saying their goodbyes, Fran and Matthew suggest some solo walks, through Acer Valley, the Winter Garden, the Pinetum or following the trail of 25 Champion Trees.
The Pinetum wins. Affectionately known as ‘Little Switzerland’ (Hillier’s father was an expert on conifers), planting began here in the 1970’s and includes many of the 84 pine species in SHHGs National Collection. Foliage grows in greens, greys, blues and yellows, in clouds and perky clumps, in dripping tumbles and shaggy fingers and weeping veils.
From the entrance back towards the bus stop, the foliage of the dawn redwood is more familiar now. When asked earlier what emblem appears on SHHG’s workwear, Matthew replied: “Sir Harold had such an affiliation with the Metasequoia, we adopted it as our symbol.”
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