Orchid fever: Enter the exotic world of Britain's favourite pot plants...and their owners

There's no getting around this – the orchid is mainly about sex. Admittedly, most flowers are: the rose is all tight buds and extravagant climaxes; the lily is a pungent phallus. But the orchid is unashamedly raunchy: it wants hot and steamy rooms; it has provocative lips; it poses like a geisha.

It is also a decidedly masculine plant: the name derives from orchis, the Greek for testicle, because the root is shaped like one. According to Greek myth, Orchis was the son of a nymph and a satyr, who attempted to rape a priestess at a drunken Bacchanalian festival. To punish him, he was turned into a flower, a throbbing ball-shaped one. In a previous life, its name was "ballockwort". So what to expect of the Royal Horticultural Society's celebrated orchid show? Knee-tremblers between the seed trays?

The exhibition takes place annually in Lindley Hall, an airy temple of Edwardian confidence in Pimlico, central London. Purpose-built for the RHS at the suggestion of the King himself, it was completed in 1904, when the empire was booming. This was a heyday for the orchid, a time when exotic flowers were a rich man's plaything. They became so sought-after that an army of ruthless "orchid hunters" would scour foreign climes for the fanciest species.

Thousands of specimens were swept from the forests of Colombia and the Philippines and shipped home. They changed hands for vast sums: in 1890, someone is recorded to have paid £1,500 for one plant – the equivalent to £100,000 today. They were carefully reared in hothouses, and grown men with names such as Rothschild and Schroder would compete to own the biggest.

Today, the orchid is as common as the muck it grows in. That is, you can pick one up for £6 at Asda, and they sell in their millions. Once considered the most difficult plant to look after, selective breeding has toughened them up, and they are now mass-produced in giant greenhouses in Taiwan and Holland. At least, the phalaenopsis is – the type most commonly seen in UK households, but just one example of an extraordinarily big family: there are about 25,000 varieties in 880 genera. An astonishing range is on display at the RHS event – big, small, elegant, hideous. But what is it about orchids that so fascinates?

"They have that exotic, strange allure," says Johan Hermans, chairman of the RHS orchid committee. "But I think what attracts people coming to the show is the variety. From tiny orchids with complex structures you can hardly see, to the big blousy phalaenopsis that everyone knows. Plus, I think there's always that slightly exclusive, mysterious, steaming jungles thing. It will always have that."

So how did orchids turn from prissy rarities to the world's bestselling pot plant? The shift came in the 1960s, with the development of meristemming. This is the process by which a core cell – equivalent to an animal's stem cell – is taken and used to produce more cells, which are then broken off and grown into separate plants. "It's mostly done in Taiwan, where they have cheap labour," explains Henry Oakeley, former president of the Orchid Society of Great Britain. "That's how orchids became cheap. You can take a meristem now, and in two years you could have a million orchids."

But even if they are now toughened-up and mass-produced, orchids still demand care, as I recently found out. Having bought an orchid as a present, I ended up looking after it for a fortnight, at the end of which the brilliant pink petals had wilted to tragic brown flakes. Oakeley reassures me that this isn't entirely my fault. The same happened to him, and, now 72, he's been looking after these flowers since he was 15.

"You do have to get the conditions right," he says. "And you have to get your watering right; it's a skill. Some orchids are very fragile and have very specific requirements – but the phalaenopsis you buy in a supermarket have been bred to enjoy the sort of conditions you and I like."

It is Oakeley who takes me around the show, the highlight of the British orchid-grower's calendar. Every kind of flower is here, from Triffid-like slipper orchids, with their deceptive, insect-trapping pouches, to the blowsy, white filly numbers such as the Oncidium Alexandra, named after Princess Alexandra on the occasion of her wedding to George V.

The show may seem peculiarly British and old-fashioned, but participants flock here from all over Europe. "It is one of the best shows," declares leading Parisian dealer Philippe Lecoufle, 65. And the passion isn't dying. Several exhibitors are in their twenties, and one vast stand has been created by the pupils of Writhlington School, a comprehensive near Bath.

I leave minutes before the doors open to the public, and pass a queue champing round the block. Those orchids may not be the rarest flowers in the hothouse, but they still know how to pull.