The Countess of Burlington's ultra-romantic gardens at Lismore Castle in Ireland

Will you take me for a walk around your garden?' was the elegant phrase uttered by the 12th Duke of Devonshire when he handed the reins of Lismore Castle to his daughter-in-law in 2007. Laura Burlington is the first to admit that, at the time, just three months married to William Cavendish, Earl of Burlington, she was a horticultural ingénue. Well-versed and immersed in visual style from the years she spent as a fashion editor at Harper's Bazaar, she was, however, unable to tell a mulberry from a maple, or a malus from a magnolia.

On the subject of magnolias, the escalating sense of drama as you process under ancient arched gateways to reach the castle is heightened by a magnificent evergreen magnolia flanking the entrance to the inner courtyard. This champion tree is the largest Magnolia delavayi in Ireland. Its creamy-white scented flowers bloom in midsummer, and it is the perfect bold, striking and achingly romantic counterpart to a panorama of battlements, castellations, turrets and towers. The walled walk is the only way into the castle, the west front of which teeters on a precipice descending to the swirling salmon-filled River Blackwater, with a view on the horizon to the Knockmealdown Mountains, which border the counties of Tipperary and Waterford in southern Ireland. The place, the names, the soft Waterford light, the gentle rainfall - everything about Lismore is dripping in romance.

As befits a house in which the 'father of modern chemistry' Robert Boyle was born in 1627, Lismore is a place of fusion and experimentation. The appearance of the castle today is largely the work of Sir Joseph Paxton and the 6th Duke of Devonshire, incorporating elements of Sir Walter Raleigh's original castle. And like house, like garden, as the seven acres, neatly divided into the Upper and Lower Gardens, are a glorious agglomeration of sustained horticultural expertise. The walled Upper Garden was first constructed by Richard Boyle, the 1st Earl of Cork, around 1605, while the more informal, woodland Lower Garden was created in the nineteenth century for the 6th Duke of Devonshire. Although the walls and terraces of the Upper Garden remain as they were when they were first commissioned in the seventeenth century, each subsequent generation has added to the patina, with much work done by William's parents. They were also pivotal in the introduction of sculpture to the garden.

The garden guide that each visitor receives charts the unique castings and pieces of contemporary sculpture that have been commissioned by William's parents since 1999, conjuring covetousness in an art lover as intensely as the glossary of notable plants does in a horticulturist. In the dusky setting of the Yew Avenue in the Lower Garden, a lonesome Antony Gormley figure looks out from the shadows, and a trio of David Nash oak columns punctuates a grassy clearing. The guide also lists follies with eccentric names, from Broghill's Tower in the top south-east corner to the Monkey Tower, situated 50 metres below in the Lower Garden.