On my first visit to New York, I never got as far as the Botanical Garden, out in the Bronx. Don't make the same mistake. It's a perfectly easy journey, only 20 minutes from Grand Central Station, on the Metro-North railroad to the stop called Botanical Garden. Before you get off, you'll probably see the centrepiece of the garden, an astonishing conservatory, completed in 1902, which makes a great curving C of glass, bending round a courtyard.
This summer, the conservatory has been transformed into an ever-changing homage to Monet. The façade of his green-shuttered house in Giverny has been recreated, along with the Grande Allée, where, as in the real garden, plants change with the seasons: iris giving way to dahlias, nasturtiums replacing forget-me-not. There's a copy of Monet's famous footbridge, swathed in wisteria, rose-covered arches and masses of geraniums. In the gallery of the garden's library, you can see two rarely-exhibited paintings by Monet – both of iris – and one of his wooden palettes, still daubed with the brilliant colours of his garden flowers.
The pool in the conservatory courtyard, of course, is filled with sumptuous water lilies, the subject of so many of Monet's paintings. "I had planted them for the pure pleasure of it," he wrote, "and I grew them without thinking of painting them... And then, all of a sudden, I had the revelation of the enchantment of my pond. I took up my palette. Since then I have had no other model."
But Monet's water garden lay on the far side of the road that divides the property. Even in his day, the road was a busy one and unsurfaced. The constant traffic created clouds of dust which settled thickly on the water lilies. Even plein-air painters have their breaking points and eventually Monet paid for the road alongside the garden to be tarred.
When you look at his water lily paintings, remember his gardeners, who worked equally obsessively to keep the pond in a condition fit to be painted. Punting out in a flat-bottomed boat, they scooped up the green algae that threatened to tarnish the pool's reflective surface; they fastidiously removed any leaves shed by the weeping willow; they rinsed debris from the water lilies' shiny leaf pads; they pruned and trimmed the growths so that the plants did not spread too far over the surface of the water.
But Monet was gardening in a Golden Age for horticulture. Glass became cheaper so more people could have greenhouses. Newly invented rubber hose made watering easier. New industrial techniques produced better knives, clippers and of course secateurs, a French name so anglicised we forget that this essential bit of gardening kit was invented in France in 1881, hand-forged in the city of Moissac, Tarn-et-Garonne. Initially they were produced for pruning vines, but they came in handy for roses as well.
Roses were being hybridised at an astonishing rate when Monet was planting up Giverny. The first Hybrid Tea rose had appeared during the Impressionist era, developed by the French nurseryman, Guillot Fils. It was a silvery-pink flower patriotically called 'La France'. "One of our national glories," trumpeted the Revue horticole of 1866.
Plants of all kinds became available in staggering quantity. Though plant hunting had been going on throughout the 19th century, the newly-invented technique of hybridisation produced bigger, showier varieties of many garden plants, especially phlox, zinnias and peonies. Superb catalogues were produced by nurseries such as Vilmorin-Andrieux in Paris, Cayeux who grew magnificent iris in the South of France, van Houtte in Ghent, Veitch in London, Kelways in Somerset (they specialised in peonies). Monet and his friend Gustave Caillebotte frequently visited botanic gardens and the trial grounds of plantsmen and seedsmen.
Geraniums were also favourites and Monet, Caillebotte, Pissarro, Cézanne and Manet all painted them. But being tender, they needed to be brought on under glass before they could be bedded out for summer and until glass itself became cheaper, geraniums remained a luxury item. The boom came with the introduction of variegated plants. Silver and gold zonal pelargoniums became archetypal flowers of the period, extensively used for carpet bedding. Already by 1905, a keen gardener could choose between 124 different kinds.
The fervour for plants and gardens infected New York as well as Europe, sending a serious young American couple, Nathaniel and Elizabeth Britton, on a visit to Kew Gardens in London. On their return, they worked tirelessly to set up a similar establishment in America's capital city. 'Great Garden Needed' thundered the New York Herald. 'Awaiting the Leadership of a Citizen Who Would Embalm His Name in Flowers'. By June 1895, enough subscriptions had come in to start work on the iconic conservatory. A misty photograph of 1897 shows Andrew Carnegie and JP Morgan, who seemed to have a hand in everything that happened in New York at that time, standing in the 250 acres of wilderness that in little more than a hundred years has been transformed into a superbly maintained garden.
The Monet show goes on until October and the impressive thing about it is the way, like Monet's own garden at Giverny, the displays shift with the seasons. The iris, shown in the paintings at the NYBG show, was a signature plant at Giverny and Monet had them planted in long lines alternating with lavender. But he loved dahlias, too. And chrysanthemums, which his friend, Gustave Caillebotte, collected. "For months at a time," wrote the critic Arsène Alexandre, "this artist forgets that Paris even exists; his gladiolis and dahlias sustain him with their superb refinements – but cause him to forget civilisation".
As summer moves on, both dahlias and chrysanthemums will become important features of the NYBG show. As will geraniums. So, if you are in New York this summer, don't miss the Botanical Garden, which is open Tues-Sun, admission $20. For more information go to nybg.org. For a taster, read The New York Botanical Garden (Abrams £29.95) edited by Anne Skillion and the NYBG president, Gregory Long.