Gardens: Highland fling

August in Scotland may be a bad month for grouse, but it is a brilliant one for flowers: fuchsias, geraniums, begonias, petunias, busy lizzies pouring out of tubs and hanging baskets and bedded out in searing combinations in the most unlikely places. Perhaps it's the unlikeliness that pleases so much. Who, driving along the A832, the tough, lonely road that connects Inverness with the west coast of Scotland at Kyle of Lochalsh, would expect to come across a garden blazing with spiky purple dahlias, the rest of the ground in front of the low stone cottage bedded round with the brightest annuals that packets of seed can provide? If you are going that way, look out for it at Lochluichart.

It's a look you don't see so much in England any more. Is it the shorter growing season in Scotland that encourages these magnificently defiant summer shows? I'm not talking corporate bedding here. That exists everywhere: roundabouts inappropriately planted up with annuals and sponsored by the local Wimpy. The look that entrances me is a private matter, one gardener in his own garden creating this wild whoopee of colour before darkness falls again.

It probably will be his rather than hers. From random observation of these plots (and they are meant to be observed, otherwise they'd be at the back not the front) I more usually see a man purposefully dead heading, hoeing, than I do a woman. An oldish man too. Will these extravagant displays die out with the generation that created them? I was too late, unfortunately, to catch Rob Young's front garden at Nisbet in Roxburghshire. A few years ago, a reader, Anne Crabbe of Chesham, Bucks, sent me a photograph of it, a classic little stone estate cottage with dormer window eyes looking out over an astonishing front garden packed with pink and red begonias interspersed with orange and yellow annuals. Driving north last month I finally had time to make the detour and found the cottage. But Mr Young had gone and his front garden had died with him.

So I cheer when I pass pillar-box red begonias defiant in the prim main street of Muthill and ranks of acid yellow snapdragons in Crieff. I'd book into the B&B on the A87 at Invergarry purely on account of the brilliant ribbons of yellow and red annuals that line the path to the front door.

In fact, I'd booked into somewhere quite different, the Kinloch House hotel by Blairgowrie in Perthshire to check out something else that Scotland excels in: walled kitchen gardens. It's a handsome early Victorian house, with a view out over Loch Maree; behind, on a south-facing slope, a big walled garden was added in the late 1860s. The approach is through a dark tunnel of vast, sprawling rhododendrons on a path that brings you to an incredibly formal entrance – wide stone steps, stone scrolls supporting a huge slab of stone above the door and a proper bell pull set into the stone surround on the right, just as though this was somebody's front door.

All walled gardens have a particular sense of privacy, particularly the ones in Scotland, set as they so often are, some way away from the house. The one at Kinloch House has been brought back to life over the past 10 years with an ambitious central roundel of flowers, divided into four big quarter circles. There was plenty still in bloom (astonishing lilies that seem to grow much better in Scotland than they ever do in England) but little sign – apart from big beds of herbs – that anything was being grown in the rest of the garden for the hotel kitchen. I had a terrific dinner there, though – crab, followed by turbot with a double whammy of raspberries for pudding, half of them made into a little sorbet sitting in a ginger snap basket, the other half miraculously turned into a soufflé that didn't sink when it came to the table. How do they do that? (And to those cynics who assume this must be a puff in return for a free bed, it isn't and it wasn't.)

None of this – the delight in other people's front gardens, the poking about in old walled gardens (there's another good one at Kinnaird in Perthshire, a hotel on the other side of the A9 from Kinloch House) – is Garden Visiting in the accepted sense. To do that properly, you need the Scottish equivalent of the English and Welsh Yellow Book (Gardens of Scotland 2008, published by Scotland's Gardens Scheme).

The best I saw, in fact the best garden of its kind that I've ever seen in Scotland, was Cluny House at Aberfeldy, a paradise balancing just on the right side of wilderness, where there were more red squirrels than I've seen for years. It belongs now to John and Wendy Mattingley and it was Wendy's parents, Bob and Betty Masterton, who started the present garden early in the 1950s with plants propagated from seed brought back from the 1948 Ludlow/Sherriff expedition to Bhutan.

That in itself is a wonderfully romantic notion, but it would never have worked if the conditions here at Cluny, acid soil, masses of leaf litter, a generally damp climate, had not been as close to home for Himalayan plants as anywhere in the British Isles. The garden covers about six acres of a fairly steep slope, but the paths are so cleverly woven over the terrain you feel that it is much bigger. You are constantly presented with new set pieces: vast stems of cardiocrinum, stupendous trees, sheets of red-flowered tropaeolum thrown over shrubs, orange Himalayan lilies seven feet high. By August the flowers of the cardiocrinums are over, but the leaves and the seedheads are as valuable an addition in this kind of garden.

It's almost the most difficult thing of all to bring off, this sense of effortless mingling of the wild and the gardened, which is not effortless at all, but requires constant refereeing by a gardener with a really good eye. I loved the pale blue meconopsis, the kirengeshoma, the brilliant red fruits of baneberry glowing out from the undergrowth, particularly when set against the soft gingery bark of the giant sequoiadendrons that grow here. These two great trees were among the few things that the Mastertons inherited in the garden, introduced it's thought in 1853 and now the fattest conifers in Britain, 35ft round the trunk. It's not really possible to imagine that. You have to see them and gaze up at their astonishing great trunks, now 135ft tall.

I'll be back at Cluny House because it had all the signs of a garden that's good at any time of the year, plenty of primula foliage, rhododendrons, fine maples which, up there, would colour well in autumn, foliage of snaky arisaemas (my new passion), hellebores. And, although open to visitors, it still feels private. No loos. No tea room. Cleverly manipulated views over the Tay valley below. Bliss.

Cluny House, Aberfeldy, Perthshire PH15 2JT is open every day (10am-6pm) until the end of October, admission £4. For details of the Kinloch House hotel, by Blairgowrie, Perthshire PH10 6SG call 01250 884237, visit kinlochhouse.com