Inventory Garden & Designed Landscape


Status: Designated


Where documents include maps, the use of this data is subject to terms and conditions (


Date Added
Last Date Amended
Local Authority
Argyll And Bute
NS 27458 84072
227458, 684072

Glenarn contains a large and well-established horticultural collection, dominated mainly by rhododendron species and hybrids, but also featuring many magnolias. The collection is well researched, labelled and under renewal, while tree recording work has identified numerous Scottish and UK champions. Glenarn is also of outstanding historic importance for the survival of its original accession books. These document the evolution and provenance of the collection and chart the story of the garden as a whole.

Type of Site

A west coast rhododendron and woodland garden established in the grounds of an 1840s villa.

Main Phases of Landscape Development

1847-c.1860, 1927-c.1975, 1983-present

Artistic Interest

Level of interest

Although mainly known for its horticultural collections, written accounts also celebrate Glenarn's design qualities and sense of place, indicating its value as a work of art in its own right (Campbell 1983; Spencer-Jones 2007).


Level of interest

Surviving garden accession books chart the evolution of the garden, recording specimens dating from the 1850s through to the 1980s (Royal Botanic Garden of Edinburgh archive: Glenarn Garden, Rhu). It is rare for such records to survive intact, making the Glenarn examples of particular importance in this category.


Level of interest

Glenarn is renowned for its extensive and varied rhododendron collection, encompassing both hybrids and species. The collection is well documented, well maintained, labelled and propagated. The garden also contains a large number of Scottish and UK champion trees (


Level of interest

Glenarn House is recognised for its regional architectural and historic interest through its category B listing.


Level of interest

There are no scheduled monuments at Glenarn. Value in this category derives mainly from the potential for future survey or investigation to reveal further information about this landscape over time.


Level of interest

The mixed canopy of woodland and coniferous trees at Glenarn links up with adjacent plots of trees and contributes some value to the scenic character of this part of Rhu.

Nature Conservation

Level of interest

Although there are no national environmental designations at Glenarn, the site offers some nature conservation value through its participation in the International Conifer Conservation Project (

Location and Setting

Glenarn is located within the village of Rhu, a small settlement on the shore of the Gareloch, 1km west of the town of Helensburgh. Occupying a south-west facing slope above the loch edge and Rhu Marina, the 19th-century house and garden are set within an undulating landscape of secluded stone villas, mature tree-belts and private garden grounds, some of which have been subdivided for more recent housing developments. The north-eastern perimeter of the garden at Glenarn marks the edge of Rhu. Beyond, farmland and then plantations extend towards the hill summit of Tom na h-Airidh.

Glenarn retains the full extent of its original Victorian villa and garden plot, while the fairly significant tree cover connects up with adjacent woodland plots and contributes to the local scenery. The house is centrally located within its grounds and the mature trees within the garden and around its perimeter ensure a secluded setting, with just occasional longer views glimpsed through the canopy to the Gareloch and the hills of the Rosneath Peninsula beyond. A burn dissects the garden along its entire length, flowing to the west of the house. An intricate path network connects all the garden areas, including a rock garden to the east of the house, built around a rock outcrop and within the former quarry which provided the stone for the house.

The boundary is well-defined. The lower half of the western boundary is formed by a modern double-hooped top metal fence, which matches and replaces the original. Elsewhere the boundary is mainly marked by a drystone wall with fabric for repairs sourced from small on-site and local quarries.

The south-west facing aspect at Glenarn together with the influence of the North Atlantic Drift ensures a relatively sheltered, mild and wet climate. These conditions contribute to the success of the horticultural collections within the garden, which are of outstanding significance.

Site History

The first phase of development at Glenarn was the construction of the house and boundary wall in 1847. At this time, Rhu was becoming an increasingly fashionable residence for wealthy Glasgow businessmen and their families, as it was easily reached by the daily steamer sailings along the River Clyde. Mansion houses and garden plots were laid out on the hillside above Rhu, transforming the former rural landscape into one of “elegant villas…richly embellished with gardens, shrubberies, and groves” (Groome 1882-5).

Glenarn House was built for the lawyer, Andrew Macgeorge. Although not known as a horticulturalist himself, his connection with the prominent botanist, William Hooker (1775-1865), may have set the scene for some of the earliest specimen introductions at Glenarn. Popular tradition states that the veteran and much celebrated Rhododendron falconeri Hook.f. at Glenarn was grown from seed collected by William's son, Joseph Hooker, during his expedition to India and Sikkim in 1848-51 (Campbell 1983: 1; Glenarn Rhododendron Book, Royal Botanic Garden of Edinburgh archive: Glenarn).

While this remains unproven (Thornley 2002: 6-7), historic photographs and the first Ordnance Survey map of 1865 provide evidence for other aspects of Victorian garden development at Glenarn. Together, they show that by the 1860s large hybrid rhododendrons defined an open front lawn, a garden enclosure or paddock was laid out to the rear of the house and an intricate path network gave access up and around sloping, wooded grounds, forming a useful backbone for all subsequent garden development.

Although the essential structure of the garden is Victorian, the horticultural elaboration of the grounds took place later. In 1927, the Gibson family moved into the house. By this time, the garden was an “overgrown jungle, rank with ponticum, laurels, self-sown sycamore and ash” (Gibson 1967: 341). Full–time accountants by profession, and with no former horticultural training or knowledge, the two Gibson sons, Archie and Sandy, commenced what was to become a lifetime project of botanical endeavour and hard work. While Grandmother Gibson tended hens in the upper garden, Archie, Sandy, and from 1930, Archie's wife, Betty, undertook clearance work and began planting, encouraged by prominent garden owners of the day.

A significant collection of historical documents from the 1920s to the 1970s illustrates a fascinating journey in terms of both social history and horticulture. Archie and Sandy Gibson represented a new kind of garden owner in the 20th century; self-taught, hailing from the professional classes and forging ahead in a field previously dominated by the landed gentry. Via their contact, John Holms of Formakin, they met major landowners and their surviving correspondence is testimony to weekend forays to notable gardens and estates from which they came away with gifts of rhododendron plants and seed, and even, following a visit to the Balfours of Dawyck, Chinese pheasants.

Perhaps the most valuable document of this period, however, is the Gibsons' accession book, a comprehensive record nicknamed 'The Bible' which records the dates, size and source of all rhododendrons planted at Glenarn, with occasional accompanying notes regarding location and survival (Royal Botanic Garden of Edinburgh archive: Glenarn House). This has greatly informed an understanding of the historical development of the garden and a facsimile copy remains a valuable reference tool for the current owners, who continue the tradition of compiling detailed garden records.

In their first 10-15 years of work at Glenarn, the Gibsons established the core of a large and varied rhododendron collection, preferring species to hybrids (Gibson 1967: 342), but also experimenting with big-leaf crosses. They developed the sheltered lower glen and created a classic, neat rock garden in the former quarry. They welcomed members of the public to the evolving garden, and in 1936, Glenarn became one of the very first gardens in Scotland to offer continuous public access (Campbell 1983: 2). Following the Second World War, the Gibsons shifted their attention to rare or new introductions, maintaining a web of contacts with other collectors, while also cultivating other plants such as magnolias and primulas and planting daffodils by their thousand. The 1950s to early 1970s represent a peak in the garden's development, with many plants and trees in their prime, and the name 'Glenarn' becoming increasingly renowned within horticultural circles (Thornley 2002: 91).

Following the deaths of Archie and Betty Gibson in 1975, and that of Sandy Gibson in 1982, the garden's future looked bleak. Fallen trees and unchecked growth had again created a “jungle”. Commentators from the United States concluded that Glenarn was “probably doomed” (Spady et al. 1983). However, in the same year, the current owners, Michael and Sue Thornley, purchased the property and immediately set in motion a long-term garden restoration project.

At the time of writing (2013), Glenarn is again well-known among rhododendron specialists and garden enthusiasts alike. Through major clearance operations, the Thornleys created space for the collection to thrive once again, breaking up old growth, introducing younger, more vigorous specimens, and re-cutting all of the paths. They have restored garden buildings, redesigned the rock garden and continue their work in propagating, documenting, researching and expanding the collection. In 2012, a tree survey recorded a total of nine Scottish champions and six UK champions at Glenarn (, while the total accession number of rhododendron species and hybrids now stands at 702 (Thornley 2013). The garden also accommodates specimens on behalf of the Royal Botanic Garden of Edinburgh's International Conifer Conservation Programme (

Landscape Components

Architectural Features

Glenarn House was built in 1847 to designs by William Spence (Thornley pers. comm. 2013). It is a two-storey, asymmetrical, gabled villa with Tudoresque details and tall, decorative chimney cans. A refurbished, rectangular-plan coach house and circular-plan garden house (a former dairy room and tool shed), stand immediately to the north east. A pair of ashlar gatepiers with corniced, pyramidal caps mark the entrance to the garden.

To the north-east of Glenarn House, surviving sections of two of the original glasshouses have been incorporated into a new glasshouse and shade house, while a potting shed has also been restored.

Drives & Approaches

A curving entrance drive lined with rhododendrons and other flowering shrubs leads from Glenarn Road to Glenarn House. It follows the original 19th-century route to the house (First Edition Ordnance Survey map 1865).

Paths & Walks

The path network at Glenarn was mainly established by 1860 and gives access to all parts of the garden grounds (First Edition Ordnance Survey map 1865).

The Gardens

Glenarn is essentially a woodland garden, with a large and diverse collection of rhododendrons, flowering trees, shrubs and seasonal bulb flowers growing beneath a mature canopy of trees. The whole is unified by the original Victorian path network, the burn which flows along the entire garden length, and a general sense of enclosure and seclusion, due in part to the landform, and in part to the mature surrounding vegetation. Many visitors report a strong sense of place at Glenarn, forged by many decades of devoted gardening (Thornley 2002: 94).

The house occupies a near central position. There is a mainly open front lawn, while to the rear, a large vegetable and fruit plot occupies the same site as a 19th-century enclosure, either a kitchen garden, or paddock. To the west, the small burn valley is known as the Glen. A pond in the lower section with horizontal chute and cascade was re-excavated in 1992 and reformed in 2013, and is planted with iris, primulas, hostas, rheum and Gunnera. A stepped path ascends towards the Upper Glen, past veteran rhododendrons and large conifers, towards the Little Glen, near the head of the burn at the top of the garden.

Other named areas of Glenarn recall past events and practices dating to the Gibson years. At the north-west edge of the garden, Granny's Hens has long since lost its chicken coops and now features some of the Gibsons' large-leaved rhododendron hybrids, magnolia, a Rhododendron lindleyi 'Geordie Sherriff' from Ludlow and Sherriff 1939 seed, and drifts of candelabra primulas in May. Further east, Germany marks past felling work by two prisoners of war. Further downslope, Melrose was named after relations from the Borders who came to help in the garden. This area at the bottom of the lawn is planted with tender rhododendrons and a range of magnolias species, including the UK champion Magnolia rostrata, which is considered to be a threatened species in the wild (International Union of the Conservation of Nature 2013,

Along the eastern edge of the garden, Sunnyside Path connects up the higher parts of the garden with the Daffodil Lawn, due east of the house, and the large Rock Garden. Once a classic rock garden with scree, boulders, dwarf conifers and other small-scale plants, this is now a less formal garden space. Redesigned from the 1990s around a natural rock outcrop and within the shelter of a former quarry, it provides habitats for smaller plants such as meconopsis, primulas, paeonia, dwarf rhododendrons and many bulbs in season (



Maps, Plans and Archives

Ordnance Survey (1865), 1st edition OS 1:2500 (25 inch to the mile), Dumbarton Sheet XVI.4, survey date 1860

Ordnance Survey of Scotland (1861), Book of Reference to the Plan of the Parish of Row in the County of Dumbarton.

Royal Botanic Garden of Edinburgh archives, Glenarn Garden, Rhu, Dunbartonshire, comprising:

o Early Plant Book 1

o Rhododendron Book (Bible / Stud Book)

o List of Abbreviations relating to above two books

o Letter from Jim Gibson to David Ingram dated 24/01/1994 regarding donation of above and history of the garden


Printed Sources

Campbell, I. (1983) Glenarn and the Gibson family. Rhododendrons with Magnolias and Camellias, Royal Horticultural Society, pp.1-5.

Gibson, J.F.A. (1967) The garden at Glenarn. Journal of the Royal Horticultural Society, Vol. XCII, 8, pp.341-347.

Groome, F. (ed.) (1882-85) Ordnance Gazetteer of Scotland: A Survey of Scottish Topography, Statistical, Biographical and Historical, [accessed 04.11.2013].

Hammond, J. (2013), Unpublished correspondence with Historic Scotland, dated 04.11.2013.

Historic Scotland on behalf of Scottish Ministers, The Lists of Buildings of Special Architectural or Historical Interest.

Land Use Consultants (1987), Inventory of Gardens and Designed Landscapes in Scotland, vol. 2, Edinburgh: Historic Scotland, Scottish Natural Heritage.

Spencer-Jones, R. (2007), 1001 Gardens You Must See Before You Die, London: Cassell Illustrated.

Spady, H. et al. (1983), Some British Rhododendron Gardens 1982, Journal American Rhododendron Society, Vol. 37, Issue 4 [accessed 05.11.2013].

Thornley, M. (2002) Glenarn: a Scottish West Coast rhododendron garden. in Argent G. and McFarlane M. (eds) Rhododendrons in Horticulture and Science, Edinburgh: Royal Botanic Garden Edinburgh, pp.86-94.

Thornley, M. and S. Thornley (2013) Glenarn, the garden in 2013, Rhu, Helensburgh. Leaflet for garden visitors.

Thornley, M. (2013), Unpublished correspondence with Historic Scotland, dated 06.06.2013 and 21.12.2013.

Internet Sources

Glorious Gardens of Argyll, [accessed 05.11.2013].

The International Conifer Conservation Programme, Royal Botanic Garden of Edinburgh, [accessed 04.11.2013].

The International Union for the Conservation of Nature (IUCN) 2013 Red List of Threatened Species. Version 2013.1, [accessed 30.11.2013].

The Tree Register, [accessed 04.11.2013].

About the Inventory of Gardens and Designed Landscapes

Historic Environment Scotland is responsible for designating sites and places at the national level. These designations are Scheduled monuments, Listed buildings, Inventory of gardens and designed landscapes and Inventory of historic battlefields.

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Printed: 18/04/2024 14:04