Northern rock: Hard work and good timing have transformed a Cumbrian garden

It was kind of David and Gail Sheals to spend so much time showing me round their Cumbrian garden. Outside their back door stood a mountain of cardboard boxes, packed with 300 small pots of Ilex crenata. The dreaded blight had killed all the box hedging in a part of the Sheals's wonderfully intricate garden and they hope that the little ilex, much used for topiary in Japan, will prove to be a suitable replacement. If I'd been them, I would have been dropping hints about the best route to the motorway, so I could start planting. But no. They even offered coffee.

Their garden, made over the past 14 years round a former rectory at Nook, near Lupton, is a perfect example of the luck that brings the right people to the right place at the right time. When the Sheals took over Summerdale House, the house was almost derelict. The bank rising behind the 18th-century building was a wilderness of bramble. The yard between house and outbuildings was mostly concreted over and though the garden itself was bounded by good stone walls, there was little worth keeping in it, apart from a few fine trees.

Few people would have had the patience to chip away at the concrete of the yard, lift all the setts and pebbles and re-lay the whole thing. But the Sheals did. And then continued throughout the garden to lay paths of extraordinary beauty, setting cobbles, pebbles and thin slivers of slate in patterns between the superb great stone slabs once quarried from the Cumbrian limestone. This is the first year, said Gail, that they haven't had a path to work on. I entered the yard under a fragile stone arch draped in clematis and the wonderful texture of the cobbled floor stopped me in my tracks. I thought it had to be original. It's that good.

Ahead was another wonderful sight, a stand that looked like an old cupboard with its doors knocked off, filled with shelf upon shelf of auriculas, each in its own clay pot. If you've never grown auriculas, you've probably seen pictures of them. They're a special kind of primula, once extensively grown by weavers and cutlers and other enthusiasts in the industrial cities of the north. The flowers bloom in colours that no other flower can match: weird gingers and mustards, grey, pale green, smudgy mauves and faded crimson. They are not easy, but Gail reckons she grows 90 different kinds. Already, I was rather in awe of the Sheals.

Turning left from the yard, you come into the front garden under the branches of a vast red-flowered japonica, with the symmetrical stuccoed façade of the house on the right and the garden sloping gently down to a yew hedge. Vast fat pillars of Irish yew guard the exit. Down the centre runs a path (made by the Sheals, of course) with lawn either side. Under the high stone wall on the left is a wide border, sparkling, when I was there, with tulips in boiled-sweet colours – pinks and mauves and a luscious deep purple. Huge mounds of lupin, phlox, geranium, monkshood, delphinium and catmint showed that the border worked hard for its living all the way through the summer.

Easing through the two yew pillars you emerge at the bottom boundary where a surprise pond fills a corner, its edges beautifully disguised with rheum and meconopsis, ligularia and variegated iris.

A path leads you back up towards the house past a another long border, a match for the left-hand one, but planted mostly with white flowers – the dangling lockets of dicentra, white-flowered brunnera, all set off against the greyish foliage of a weeping pear. A huge laburnum is one of the remnants of the original garden.

The Sheals are great hedge planters and the process of dividing up their space is still going on, with lines of young yews, beech and hornbeam making ever more intricate interlocking spaces in their acre and a half. "It means that each section can then be a little different," explained David Sheals, who recently gave up his work as a radiologist and is now as bound up in the garden as his wife. This side of the garden was once dominated by a huge cedar of Lebanon, which was lost in a storm. Once the wailing was over, the Sheals realised it released a welcome amount of new planting space. They've made two short summer borders in hot colours and in the long grass beyond, planted a small grove of birch trees with cowslips and wild orchids growing underneath. Cumbrian limestone provides a wonderful underpinning for a wild flower meadow. It keeps the grass short and fine. The only problem is finding a place where you can excavate a hole deep enough to plant a tree. Beyond the garden, the huge rounded bulk of Farleton Knott dominates the view, a reminder of the tough land from which this garden was won.

At this stage, the Sheals led me through to their nursery. A nursery was never part of the original plan, but Gail Sheals loves propagating. With an empty garden to fill and no money, she grew most of her plants from seed. She found she had the knack of making things grow and instead of giving away her surplus plants, started selling them. Now she specialises in primulas (the best plants I've ever seen) and shade loving perennials. For a while the Sheals's daughter helped with the nursery. Now she's decamped to set up her own. Which gave David Sheals a good reason to retire.

At the back of the house is a sloping woodland garden. The atmosphere here is very different, with huge old fruit trees providing shade for intricate carpets of woodlanders underneath. Yellow-flowered azaleas bloom above carpets of bluebells, 'Paul's Himalayan Musk' rose throws its great arms up into a pear.

I don't suppose the Sheals ever sit up here – they didn't strike me as the sitting sort – but if you go to the garden (and you should), look for a hidden seat behind an apple log wall. It's got a stunning view of Farleton Knott.

The garden at Summerdale House, Nook, nr Lupton LA6 1PE, is open tomorrow and also 20 & 27 May (11am-5pm), admission £3.50. The nursery is open every Thurs, Fri and Sat (9.30am-4.30pm) until 10 Sept. For more information, call 01539 567210 or go to the website, summerdalegardenplants.co.uk