RHS Wisley has gorgeous borders if only those 12ft begonia eyesores would give them a chance to shine

My mum and I are in the car park at Wisley, the RHS's flagship garden just off the A3 in Surrey, trying to work out how to find our way to the ticket counter. The car park comprises vast acres of tarmac in compensatory acres of Lord of the Rings woodland glade, criss-crossed by a slightly confusing network of paths. Since last I visited, the car park has been organised with highly tasteful dividing lines, gauzy ribbons of verbena bonariensis, wheaten grasses and pale yellow daylilies. We begin to feel optimistic that we are in for a good day just wandering its ranks.

And then, through the greenery, we both spot something orange. Not something small, either. More like two traffic cones stolen from a drunken night out on the town by Shrek's gigantic girlfriend. They are actually luminescing at us through the trees. As we get closer, we realise that the traffic cones really are gigantic. Each one is about 12ft high. And each is made up of hundreds of begonia plants in various shades of orange and yellow. And here are our fellow visitors, marvelling at them. "Ooh, I don't know how they've done that," one remarks, walking round it, studying the planting up close. ("Oooh, I don't know why they've done that," my mum and I wonder.) No one is marvelling at the gorgeous borders in the car park. They've been blinded by the begonia homing beacons.

The summer holidays do generally mark the disappearance of anything conventionally tasteful from the garden, it's true. These months rev up a display of red, orange and yellow plants for which sunglasses might sensibly be prescribed. Daylilies, red-hot pokers and dahlias all have their contribution to make on the gaudy front. But it must be possible without resorting to begonias, surely? They aren't even nice begonias, such as "Bonfire", with its little orange flowers and ivy-shaped leaves. They are great big tuberous ones with blooms the colour of cycling bibs.

Luckily, our visit does become more tasteful as it goes on, even for a pair of fusspots as my mum and me. In the long borders leading uphill, the gardeners try to restrain themselves, with cannas and dahlias in bronzed tones. Elsewhere, though, the full firepower of August is on show. On the lawn by the Conservatory Café, daylilies, including "Berlin Red" – a real stonker; dinner-plate-sized Achilleas in rape-seed yellow; and red-hot pokers in tones just slightly more muted than the full orange special we're used to. Though if I didn't know they were plants beyond the realms of good taste, I might be tempted to say "Apricot Sky", and "Maid of Orleans" are both almost verging on pretty.

Wisley is open Monday to Friday 10am-6pm, and weekends 9am-6pm (www.rhs.org.uk)

Grandly garish

Crocosmia 'Lucifer'

Famous and ubiquitous for a reason: it's a great, hard- working plant, with gigantic stems six inches taller than most other crocosmias, bearing deep blood-orange flowers that look as though they are dripping juice. £5.99, crocus.co.uk

Achillea filipendulina 'Cloth of Gold'

Tasteful when planted with paler creams and whites, but a real, colourful point of punctuation in a border of hot colours. £6.49 crocus.co.uk

Echinacea 'Tomato Soup'

They didn't mess around when they were naming this. Bright red, whichever way you look at it. If you deadhead it properly, you should have its Heinz- like hues in the garden almost until Bonfire Night. £8.99, crocus.co.uk