Border patrol: The team at Trelissick are intent on pleasing the late-summer crowd

On the verge: 'Trelissick Purple' dahlias mix with crocosmia lucifer in the Cornish garden's borders (KIRSTIN PRISK)

I'm eavesdropping again. "This is really incredible," the couple are saying. Then they turn to me. "Isn't it?" I rush to agree. We are all having our eyesight boggled by the grand borders at Trelissick Garden in Cornwall, where the glorious early September display includes the striped leaves of Canna "Durban", sitting alongside the garden's own dahlia, "Trelissick Purple".

Cornish gardens are known for their beauty in spring. You'll hear praises of their gigantic rhododendron and azalea displays sung from here to Yokohama. But the greatest number of visitors arrive in the high holiday season, along with ice-creams, boogie-boards, buckets and spades. So the county's head gardeners take seriously their responsibility to have their borders still looking good in early September.

At Trelissick, head gardener John Lanyon is definitely giving us something to wow at. The garden has always had delightful late-summer planting, as the huge hydrangea collection goes on blooming. (Lacecaps and paniculatas delight visitors with good taste, while the big moptopsa are there for those of us who still prefer our hortensias the old-fashioned way.) But Lanyon has also overseen some startling improvements. The grand borders by the gate, for example, are new for 2010. "At the beginning of the year," explains visitor services manager Hannah Darling, "people were coming in and saying, 'What are you doing here?', as the entire border was recreated from scratch. The idea was to have all-round excitement extending right into autumn." With huge dramatic castor-oil and banana plants, the effect works beautifully.

Elsewhere, there are old favourites to revisit: a sensory garden, as pretty to the nose as ever, and a fine tree collection. And for small children less delighted by a nice shrub, there are winding paths linking stupendous open views out across to St Mawes, a ha-ha big enough to camp in, a series of wooden gazebos to find and even a ride on the King Harry Ferry.

As winter approaches, Trelissick has one more treat up its sleeve: an orchard of Cornish apple varieties. The garden is currently fund-raising to buy a better cider press, and the day we visit, kindly looking ladies press us to buy raffle tickets. Apple Weekend is 2-3 October, with bobbing, apple-themed meals in the restaurant, and opportunities to taste in the stables that houses more than 300 varieties. Or come back in midwinter for a big wassail. "We dress up, choose a king and queen of wassail," laughs Hannah, "and I run round with a megaphone!" Join in the fun on 17 January.

John Lanyon will be speaking on 'Evergreens to Enhance a Cornish Garden' on 2 November, £16 including dinner. He also conducts a free garden walk the following day. Book with Trelissick on 01872 862 090

Still wowing 'em

Great Dixter, Kent

Always spectacular, but visit now for dahlias, begonias and other big leaves arrayed with spot-on colour effects, plus trademark changing displays of succulents from the greenhouse. Open till 31 October except Mondays, greatdixter.co.uk

The Exotic Garden, Norfolk

A friendly, intimate garden with high hedges to protect a tip-top collection of ginger plants, brugmansias and other treats. Open Sunday afternoons till 24 October, exoticgarden.com

Tresco Abbey Garden, Scilly

A garden worth a three-hour boat ride to get to has to be special. And it is. Acres of rarities such as aeoniums and strelitzia that can't be grown on the mainland, in arched ruins with amazing sea views. Daily, 10am-4pm, tresco.co.uk