In the footsteps of Wordsworth: In the heart of the Wye Valley in Monmouthshire, Anna Pavord retraces her past and discovers the rebirth of Brobury House Gardens

The Wye river rises in the Plynlimon hills, east of Aberystwyth and wanders south in extravagant loops before it finds the Bristol Channel. I was born and brought up just a river away from it, in the valley of the Usk. This isn't such a grand stretch of water. Going into Herefordshire from our home in Monmouthshire always felt like visiting relatives who were doing rather better in the world than we were. Tea at the Angel hotel in Abergavenny was never quite such a treat as tea at the Green Dragon in Hereford. When a local farmer made good, he would slip east over the border to richer soil and lusher pastures - an easier living.

I wandered up the Wye valley recently to visit Brobury House Gardens, a new entry this year in the National Gardens Scheme's yellow book. From Chepstow, if you are in the mood, you can abandon the fast track of the motorway and fiddle instead up the A466, which closely follows the banks of the Wye up to Monmouth. The grand set piece is Tintern Abbey where, on my first ever school outing, I was sick in the ruins. Unfortunately, the association won't go away. When I should be thinking of Wordsworth - all that fabulous stuff he wrote on his 1798 tour of the Wye: 'the joy/Of elevated thoughts; a sense sublime/Of something far more deeply interfused,/Whose dwelling is the light of setting suns,/And the round ocean and the living air,' - I'm remembering a charabanc and too much chocolate.

The Wye, at Brobury, is crossed by a long, narrow brick bridge built in 1759, one of the few bridges on the upper reaches of the Wye not swept away in the great flood of 10 February 1795. Downstream, the river melts its way through grassy meadows. Upstream, it's bordered by trees. Keith and Pru Cartwright, the new owners of Brobury House, have the Wye as the ultimate water feature, marking the southwestern boundary of their land.

The house is set high, looking directly across the river to the vicarage at Bredwardine, where Francis Kilvert, the famous diarist, spent the last couple of years of his life. The vicarage is built in a fanciful Regency style; Brobury is heftier, fake Scottish baronial, built for a Manchester man in the 1880s. So it's not surprising that the bones of the garden are late Victorian: some good trees, a wide gravel walk for the daily constitutional, strong stone steps connecting the different levels, with the bonus of fine views out over the river to the south and west, where the land beyond rises behind Bredwardine to a steepish little hill called The Knapp.

The original drive delivered visitors to the north face of the house, with the kitchen gardens on the left. Little is left of the original brick walls, but the bases of masses of brick cold frames remain. It must once have been a wonderfully productive place. The new drive delivers you to the south front, where the Cartwrights have added a conservatory and sleek new terrace to cater for wedding parties. The main part of the garden wraps round the south and west, with a mulberry, said to have been planted by Kilvert, on the front lawn.

Atmosphere, a sense of place, often comes most strongly from a collection of incidentals in a garden. The horse pond at Brobury, tucked down in the south-east corner of the garden, had it. So did the big old apple trees in the orchard - the warm colour of the apple skins, the slightly alcoholic smell of the windfalls in the grass. Seeded at the bottom of the retaining wall on the old drive was a colony of autumn-flowering cyclamen, ludicrously out of scale with the heftiness of the wall and the width of the drive, and enchanting because of it. And leading from the old greenhouses in the corner of the former kitchen garden, a clipped tunnel of pyracantha, very tall, very narrow, very memorable.

At some stage, on the flattish land close to the horse pond, a thoughtful former owner put in a formal grid of birch trees that provide one of the best inward views in the garden. I'd limb them up a little now, to augment the impression of being in some cathedral nave, the white-barked trunks making pillars that arch out above into a Gothic tracery of fine-limbed branches. But from here you look through the trees into an enclosed lawn, divided into four by paths that meet at a handsome stone urn, carved with grinning dolphins. Mentally, I found myself planting up the enclosing stone walls, south-facing, a wonderful opportunity.

At Bredwardine church on the far bank of the river, I paid my respects to Kilvert, who was proud of his new parish. 'Showed my father round the garden,' he wrote in his diary in 1878. 'He was much pleased with everything. The house and garden were much larger and more beautiful than he had supposed.' What did he make of the red sandstone lintel over the old north door of the church, carved by Bredwardine masons in the 12th century? Between two geometric roundels sit two savagely strange creatures, half-human, half-animal, fully pagan. It's a speciality of Herefordshire, this kind of carving, and the churches are extraordinary.

On a journey like this, incidentals give as much pleasure as the main objective: the Wye Valley Hotel in Tintern, smothered in a froth of hanging baskets, the grim 19th-century front forced to smile; the extraordinary splendour of the trees lining the road that leads west from Hereford to Brecon; monumental yews in village churchyards. Some un-named person has produced a handsome little series of booklets, The Leyside Yews, Yews of the Wye etc, which leads you round some good trees and some extraordinary buildings.

In the Bredwardine churchyard was a stern notice from the Parochial Church Council forbidding the use of plastic flowers on graves. That must have caused a furore in the parish. But here, I think they are right. In Byford churchyard, not far away, was what seemed to me the perfect solution, a newish grave covered entirely with white-flowered Cyclamen neapolitanum. It helped that the headstone was a good slab of slate, beautifully lettered with a name and dates, nothing else. And the cyclamen were at their best, with ruffs of marbled leaves just beginning to mass around the small flowers. But the flowers will have started in August and the leaves will be there for months more, unassuming, but entirely fitting.

The gardens at Brobury House, Brobury, near Bredwardine, Herefordshire are open every day (10am-5pm), admission £3. There's a special opening (with tea) for the National Gardens Scheme on 29 October. For further information call 01981 500229 or check out the website at www.broburyhouse.co.uk