Chelsea Flower Show: In a horticultural league of its own

From lush rainforests to plastic lawns, the Chelsea Flower Show returns later this month with an extravaganza of imaginative gardens. Sophie Morris takes a sneak preview of the highlights

The forthcoming Royal Horticultural Society's annual Chelsea Flower Show is a gardeners' Mecca. On the one hand, the show is a one-stop shop for all things gardening-related, but the real draw is the incredible display gardens which have developed in daring and innovation over the event's 148-year history. Landscape designers, plant experts and architects spend months preparing their show gardens; the green-fingered extravagances are funded by deep-pocketed sponsors.

For those of us who consider a patch of grass and a few shrubs and flowers a garden, there is plenty of advice and inspiration in the creativity on show at Chelsea, and each year throws up a bit of controversy too. Last year, it was Top Gear's James May's plasticine garden. In 1993, a seaside garden won the top prize, even though it was made of sand.

This year promises yet more squabbling, mainly due to the use of – gasp – artificial turf in one of the gardens, and another which owes more to diamond sparklers on loan from a fancy jeweller than horticulture.

Amid the contention, Chelsea always delivers when it comes to digging up anything weird and wonderful in the world of trees, plants and flowers. See our guide for this year's standout displays.

Bling is back

It seems Chelsea didn't get the memo about spending cuts. The most expensive design in the show's history, the Ace of Diamonds Garden, comes in at an eye-watering £20m, more than the total for all this and last year's exhibits combined.

The reason for such extravagance? The designer David Domoney wants to remind us of the link between plants and precious stones. The walls of the garden will be fashioned from £100,000 of semi-precious amethyst and quartz, and the flowers chosen are named after or resemble gems.

Even the mulch, mixed from glass-cut diamonds and diamond shards of metallic compounds, will be worth millions. Don't forget your shades. Another luxury item jostling for attention amid the on-message ecological and campaigning exhibits is Laurent-Perrier champagne. Here, understated opulence is blended elegantly with water and a spring woodland featuring river birch, pruned hedges, blue iris and fresh white flowers. The glimmering centrepiece is a distinctive bronze pavilion built from folded sheets of patinated copper.

Outdoor Living

Typical of the Australians to remind us of their idyllic outdoors lifestyle while we're still waiting for warmer days. Fleming's and Trailfinders' Australian Garden celebrates outdoor living with a swimming pool and spa, sunken lounge and kitchen area – a luxury living pod in the great outdoors.

The theme is continued in the Naturally Norway Garden with its kitchen, daybed and shower of unmistakably Scandinavian design, surrounded by plants hardy enough to survive the diverse Nordic weather conditions and a water feature to represent the Norwegian fjords. The Children's Society Garden was designed by Mark Gregory as a response to a survey of 7,000 10- to 15-year-olds which found they valued spending time with family and friends and relaxing in safe, attractive environments most highly, and were made unhappy by their typical local surroundings. The retreat-style garden offers space for families to enjoy time together with a covered lounge seating area around a fire pit, a plunge pool and pizza oven. Faking It

Chelsea traditionalists are outraged at the nerve of the Urban Plantaholic's Kitchen Garden made from fake turf. Apart from on a few trade stalls, artificial products have never got past security at Chelsea, never mind being used in the centrepiece of one of the show gardens. How can a synthetic "kitchen garden" yield produce?

The garden is sponsored by Easigrass, an artificial-turf retailer, and features a grotto with walls papered in the fake stuff, an element which required special permission before it got the go-ahead. In fact, its designer, Tony Smith, tried to get an entire Easigrass garden past officials, but failed. Bob Sweet, the Royal Horticultural Society head of shows development, calls the compromise "just about permissible" because it is being used as wallpaper and not instead of grass.

The design is intended to poke a little fun at city dwellers who yearn for green space and the natural world, and describes its owner as a "plantaholic bachelor who lives in the city and has a high-profile, stressful job. He wants to escape into his own private world with only his beloved plants for company."

Jungle Fever

While rainforest is bulldozed all over the world – both legally and illegally – the Chelsea gardeners are busy planting their own. There will be three jungles at the show this year, hopefully enough to educate visitors on the parlous state of the real thing.

James Wong, the presenter of BBC 2's Grow Your Own Drugs, is showing a Malaysian garden inspired by the country's rural kampung village way of life, but presented in a contemporary urban courtyard setting. Edible green stuff such as banana trees, coconut palms, yams, gingers and lemongrass will be joined by pitcher plants, peacock begonias, matonia ferns and endangered bat lilies, all rare native Malaysian species.

The chocolate producer Green & Black's is supporting the Rainforest Garden, which recreates the tropical plant life of Cameroon, helping to raise awareness about the threat to the jungle and its indigenous inhabitants. The design as well as the foliage is political, telling the survival story of local tribespeople as their lands are destroyed by logging, mining and hunting. Plants which look like rainforest specimens but are suited to Britain's climate also feature, showing how we can get a similar look in our gardens.

The third patch of jungle can be found in the Great Pavilion as part of the World Land Trust's display of Atlantic Rainforest, which is in far worse shape than its Amazonian counterpart (93 per cent destroyed) but receives scarcely any publicity.

All three mark 2010 as the UN International Year of Biodiversity, and give visitors a rare chance to view specimens at risk of disappearing for ever.

Size matters

The Eden Project is snaffling the crown for Chelsea's biggest garden yet – twice the size of last year's entry and 600 sq m in total. Eden's biospheres in Cornwall are the educational charity's traditional focus point. At Chelsea it is seeking to highlight our interconnectedness with every component of the natural world, and it has a lot to cover: crops, food, floristry, leisure, medicine, industry and conservation all feature. More than 600 homeless people will help build the Places of Change Garden next week.

Statement design

Chelsea wouldn't be Chelsea without a lot of showing-off from designers and architects, evidenced in part by the impressive outdoor buildings on display. In Robert Myers' Cancer Research UK Garden, an ornamental urban roof garden, a bold 15ft slatted canopy offers shade. Over at the M&G Garden designed by Roger Platts, there will be a summerhouse carved from Sussex oak and there is a striking bronze pavilion in Tom Stuart-Smith's Laurent-Perrier Garden.

Dying arts

Rural crafts are on the at-risk list along with trees and plants. Three designers are transporting the ancient art of dry-stone walling into their show gardens. Tom Stuart-Smith's garden is full of it. In the Stephen Hawking Garden for Motor Neurone Disease, a clock is set into a dry-stone wall and water pours out into a dark hole, representing the passage of time into oblivion, which equates to one diagnosis of the disease being like falling into a black hole.

RHS Chelsea Flower Show 2010 runs from 25 May to 29 May at the Royal Hospital, London (Rhs.org.uk)