Anna Pavord: 'Dan Pearson conjured up drama on the Chelsea Flower Show's triangle site'

Pearson's monumental evocation of the rockery and trout stream at Chatsworth won Best in Show

There were two outstanding gardens at the Chelsea Flower Show this year: Dan Pearson's monumental evocation of the rockery and trout stream at Chatsworth, which won Best in Show, and James Basson's recreation of a perfumier's garden in Grasse, which won a gold medal. As installations, they could not have been more different, but what they had in common was a sense of truth. Both gardens were made by designers who have trained themselves to properly look at landscapes – both natural and man-made – and to understand how they co-exist.

Basson's show garden made brilliant use of tufa, cut into blocks to recreate the narrow channels that bring water into the cultivated plots of Provence. In the corner was a simple clay-tiled lavoir, the communal washing place once a feature of villages here as well as in France and Italy. Ferns flourished in the damp shade of the building, which provided a dark, mysterious contrast to the bright, open aspect of the rest of the garden, where either side of a simple earth path, the perfumier's once tidy rows of scented plants – roses, sages, lavender, gardenia, jasmine – had been subverted by self-seeding poppies, teasels and sprays of woad.

The garden was a masterpiece of observation, tact and understanding. Basson lives in Provence, but you could have lived there all your life and never noticed or absorbed the texture of the landscape, the detail of plant communities, the acute sense of place that Basson so brilliantly translated to the Chelsea show.

And then there was Pearson and the drama that he and Chatsworth and Crocus (the contractors) conjured up on the potentially difficult triangle site at Chelsea. Show-garden plots are usually variations on a rectangle, most of which you look into from a short side and a long side. The triangle (actually more the shape of an orange segment) sits on its own at the bottom of Main Avenue. It is much bigger than the other sites and you can walk all the way around it.

Chatsworth, the Duke of Devonshire's house in Derbyshire, provided the rock, the same gritstone that Chatsworth's famous gardener, Joseph Paxton, used for the rockery he built at Chatsworth in the 1840s. Rockeries were the height of fashion then but, as Paxton wrote in the Magazine of Botany, "no subject in the gardening profession [calls] for a more vigorous exercise of skill and talent".

The rocks Pearson used were left over from Paxton's vast creation, and were lying in the Derbyshire undergrowth, attracting soft layers of moss and liverworts, even wild flowers. Astonishingly, this overlay survived all the handling, craning, and shifting necessary to stack the rocks into the dramatic tors Pearson had envisaged. They rose majestically between the equally mature trees that looked as though they must always have been on the Chelsea triangle. From a well disguised pool, water trickled over the face of a rock into the narrow stream that wound through the site, with absolutely convincing grassy banks either side.

Convincing was the point. I listened to contractors from another garden discussing how the water had been persuaded to do what it was doing. "Look," one said to the other, "he's even got that scouring out effect. Sand along the stream bed at the middle. The pebbles pushed up to the edges either side. That's exactly how it happens."

Those used to landscaping say that big rocks tell you where they want to sit. But you still have to have ears that can hear them. The rock-work on Pearson's garden was stupendously good: dramatic, yet believable, the curious buff colour of the stone beautifully matched by big bushes of enkianthus in full flower. It's not a shrub I've ever taken much notice of, but here it was brilliant, with hanging clusters of small, bell-shaped flowers, slightly cream, slightly buff, slightly pink, the colour of faded plush.

The strongest scent came from big, rangy old bushes of the yellow azalea, Rhododendron luteum, well settled in among the rocks, with scatterings of campion around them and lily-of-the-valley tucked under their branches.

Walking round the site you were given a masterly sequence of different views into it. One view along the stream gave you superb stands of the royal fern (Osmunda regalis) and the darkly suffused leaves of rodgersia. Another view led through to bright pinpricks of colour from candelabra primulas in magenta and brick red, planted close to the stream, together with an elegant dark-stemmed iris "Dark Aura". That wasn't even in flower, but it still pronounced itself a star, the thin wrapped buds peering out from the leaf axils like birds' beaks.

The planting, as well as the landscaping, balanced triumphantly on the most difficult of tightropes. The design was arresting, but absolutely believable. The planting was complex, yet showed great sensitivity to the way things happen in the wild, particularly the way that a plant seeds itself out from its starting point. Pearson was not afraid to keep planting in some areas quite sparse, as if the underlying soil were the restraint.

The key plants he had chosen were most usually species rather than varieties – Hydrangea villosa, Aralia cordata, Styrax officinalis, Acer campestre – splendid creatures, spanning the divide between the gardened and the wild. White bladder campion spread under ravishing martagon lilies. Acid-yellow smyrnium pushed up through the branches of a pink dog rose. Paxton took several years to make his rockery. Pearson had just 18 days. Triumphantly, he has pulled off the most difficult trick of all: to make the made look not made. Will anyone else ever dare to take on the triangle again?

The number of show gardens at Chelsea provides a novel way of feeling Britain's financial pulse. In 2009 (the worst ever at Chelsea in terms of numbers) there were just 13. In 2007 and 2008 there were 20. The glory year was 2000 when there were 23. Millenium money. This year, as in 2013 and 2014, there were 15 show gardens and seven of them got gold medals. Together they will have cost their sponsors about £7m. Money well spent? Of course I'm going to say yes.

WEEKEND WORK

WHAT TO DO

* Put in Brussels sprout plants. Choose plants that have been grown in the open ground if possible. They make straighter, tougher plants than seedlings grown in trays.

* Split up large clumps of primrose and polyanthus tearing the clumps apart into several separate crowns with roots. Replant the pieces in fresh ground with a handful of bonemeal to speed them on their way.

* Cut out frost-damaged or dead wood from abutilons. You can keep them under control by cutting back two thirds of each new shoot any time over the next month.

* Thin out congested clumps of bamboo now by cutting away some of the old canes at the base.

* Clip away scorched leaves from bay trees in pots and refresh the compost by scraping away the top couple of centimetres and replacing.

* Continue to sow annuals where they are to flower outside.

WHAT TO SEE

The Chelsea Fringe continues until 7 June, with an array of events such as Oh Beehive at Sussex Prairies, where from 1-7 June there is a week of bee-related activities (not 2 June): Details at sussexprairies.co.uk. Information about other Fringe events, at chelseafringe.com