Dyffryn House (nprn 18592) is a large mansion in French Renaissance and English Baroque styles situated in gently rolling countryside approximately 2km south of the village of St Nicholas in the Vale of Glamorgan. Although a park and gardens have existed around Dyffryn House since at least the eighteenth century, the site is best known for its Edwardian gardens, considered to be the grandest and most outstanding example in Wales, comparable to some of the most extravagant gardens of the period in Britain. They are the result of a remarkable partnership between two outstanding men of their generation - the owner and horticulturist Reginald Cory and the landscape architect Thomas Mawson. Cory was not only interested in garden design but was also an exceptionally talented horticulturist and plantsman. The structure of the gardens, combining the expansively formal and the intricately intimate, survives almost in their entirety, with some later modifications within the general framework.

House and gardens lie within a small park (700370) which was reduced from 1905 onwards for the creation and expansion of the gardens. The Edwardian gardens were initiated from 1891 onwards. The first garden was modest, with a balustraded terrace along the south front of the house, formal beds and a tennis lawn surrounded by Irish yews on a further balustraded terrace. To the east of the house was a formal 'panel garden' laid out with Irish yews. These elements were retained in the plan for the gardens by Thomas Mawson who was commissioned in 1903-04. The formal and compartmented gardens were largely laid out after 1906. The spacious grandeur of the main terraces, lawns and canal (with its central fountain, 23074) to the south of the house is contrasted with the intimacy of the garden 'rooms' to the west, and all parts are cleverly interlinked by paths and steps. The garden is tied to the house by a strong central north-south axis dominated by the canal. Cross axes link the central open space with the arboretum to the east and compartments to the west.
The gardens extend to 36.4 hectares and contain areas of very different character. To the north-east of the house a flight of rustic stone steps lead up to a rockwork water garden (created in the 1950s) with twisting paths and steps, rockwork pools and cascades. To the east and south-east of the house the ground rises gently and is laid out as an informal arboretum, with open glades and more wooded areas. Some of Cory's most notable trees grow in this area. A heather garden, planted in the 1970s, is situated towards the north end. To the south and south-west of the house the garden is very grand and formal, with intimate compartments in eclectic styles flanking the west side of the large open lawn in the centre and with more informal areas along the west and south sides. On the west side the intricate arrangement of compartments, paths and steps leads up a gentle slope at the north end to the older walled garden (23077).

Within the gardens are many notable trees, including some very early introductions. They date from the sixteenth-seventeenth century; late eighteenth-early nineteenth century; 1891 and 1905-31. Many newly arrived plants from countries such as China were grown at Dyffryn.
Evidence of an earlier garden layout was revealed through aerial survey in the form of cropmarks on the north side of the river Waycock (415558). 

Sources:
Cadw 2000: Register of Parks and Gardens of Special Historic Interest in Wales, Glamorgan (ref: PGW(Gm)32(GLA)).
Ordnance Survey first-edition six-inch map, sheet: Glamorgan XLVI.11 (1885).
Ordnance Survey first-edition six-inch map, sheet: Glamorgan XLVI.11 (1901).  

RCAHMW, 15 July 2022