The Impressionist painters never intended their garden paintings to be botanically precise. But in the magnificent exhibition, Impressionist Gardens, now showing at the National Galleries in Edinburgh, you are left in no doubt as to their favourite flowers: hollyhocks, chrysanthemums, dahlias, gladiolus, sunflowers, iris, lilies, waterlilies of course, poppies, geraniums, roses, nasturtiums. Especially nasturtiums, which Degas proposed should be the symbol of the Impressionist group, partly because their first show had been held in a studio on the Boulevard des Capucines in Paris, partly because of the flower's exuberance, its glowing colours.
They could equally well have chosen dahlias, which had been popular in France long before the Impressionists started painting them. Monet was mad about them and planted them with orange nasturtiums and mauve asters either side of the Grande Allée, the broad gravel path down the centre of his famous garden at Giverny. Monet went to Giverny in 1883 when the market for his paintings began to revive and stayed there for the rest of his life. By 1890, he was said by Octave Mirbeau, Monet's favourite art critic, to be "in a fury of horticulture". Already by 1892, he had six gardeners.
But as well as his chief preoccupation, the garden became his chief subject. Three quarters of the paintings he made in the last 26 years of his life were of his garden. In the once solidly respectable market plot (the deep alluvial soils at Giverny were ideal for vegetable growing), poppies replaced the cabbages; irises and marigolds filled the onion beds. His neighbours were deeply suspicious.
When Monet bought more land on the far side of the road and started to make his famous water garden, suspicion turned to open hostility. Representations were made to the prefect of the Eure. "Blow art. What about our water?" asked the Givernois. Monet got his lily pond, but the locals never quite forgave him. They charged him to cross their fields. They chopped down poplars, dismantled haystacks when he was in the middle of painting them. Making the pond, though, was more tortuous a process than he imagined. "I don't want any more to do with it," he wrote in a letter to his wife, Alice, on 20 March 1893, "what with all these Giverny people, and then the engineers and diggers."
This is all very reassuring. Gazing at the artist's translucent canvases, it is easy to forget that the tranquil, seemingly timeless lily pond was born out of conflict and hard labour. When the digging was over, dozens of bamboos, cherry trees and ferns were planted round the banks and masses of water lilies, carefully graded in colours, set in the pond itself.
Many of the best new breeds of waterlily were developed by Joseph Bory Latour-Marliac who had a nursery south of Bordeaux in the village of Temple-sur-Lot. He took all the known European species, including an unusual red variant of Nymphaea alba, found on a Swedish lake, and using this gene pool, developed a new race of hardy hybrids introduced from 1893 onwards and still around today.
The garden provided constant inspiration for Monet's incomparable canvases, but should gardeners take it as an equally compelling model? Only up to a point. The disadvantage of the Giverny style is most evident in winter. After the delicious profusion of snapdragons, campanulas and morning glory melts in the first frost, there is not much left to sustain you.
The layout of the long, thin market garden beds provided a series of very pretty paintboxes for Monet. But not a design. The planting, made up to a great extent from flowering annuals and tender exotics, is labour intensive (too much so for most amateurs – however passionate) and there is little of the structural planting that in the best-planned gardens provides a backdrop for more ephemeral foregrounds.
The lack of design is not evident in Monet's paintings because he chose to paint his garden section by section as each bit came into season. And the paintings are nearly all made in late spring and summer, by which time his army of gardeners had conjured action from the earth. There was a lot to conjure. "Sowing," he scribbled in a note to them in 1900. "Around 300 pots poppies – 60 sweet pea – around 60 pots white agrimony – 30 yellow agrimony." He was using plants like paint – laying on swathes of them in great masses. The hard lines of beds dissolved in pulsating masses of colour.
Le Figaro published a fulsome article on the Giverny garden in 1901, but not all visitors were impressed. The English artist, Sir Gerald Kelly, gave it nil points. "It was nice and large and covered with rambling crimson roses which, you know, you get practically speaking in any suburban garden all over England. And there was a little piece of water where there were some common or garden water lilies". A plant snob, evidently, Sir Gerald.
But there were others who thought that the most beautiful garden in Giverny was not Monet's but the one at the old priory. This belonged to the American artists Frederick and Mary MacMonnies, who became part of the colony of Givernistes in 1890. Their place, generally known as the MacMonnastery, was a favourite setting for the American Giverniste's paintings of nudes, the models brought down from Paris. One of them, naked, once opened the garden door expecting an artist neighbour and instead found standing there a Presbyterian minister visiting from Virginia.
But who would I most like to spend time with in a garden? Camille Pissarro, of course, a friend and contemporary of Monet's (though 10 years older). There's a touch of megalomania about Monet's 300 pots of poppies to be sown by his six gardeners. Pissarro the anarchist is a more sympathetic figure. Though not himself a gardener, he was a superb observer, especially of kitchen gardens and the people who worked in them. "Beauty is everywhere, if you know where to look for it," he said. Pissarro – he's my man.
Impressionist Gardens is at the National Gallery, Edinburgh, to 17 October. For more information call 0131 624 6560 or visit nationalgalleries.org