The RHS Chelsea Flower Show is always something of a fluid event, but last year was just ridiculous. Perhaps wary of another washout, water features intentionally in many of the gardens this year. “The water features will be spectacular - much larger than we're used to seeing,” says Robert Sweet, the show organiser.

Now “large” sounds dangerously vulgar, but this is Chelsea: the start of the London season and the high point in the calendar of the Royal Horticultural Society. The Queen visits

(although she's rumoured to prefer race courses to gardens). So don't expect B&Q-style bubble pools (or patio heaters - they've been banned).

Robert Myers, who won gold last year for his Fortnum & Mason garden, has designed a garden for Lord Cadogan (who owns great chunks of Chelsea). Set in the future, A Cadogan Garden assumes London is warmer and wetter. A canal flows through lush planting. A statue of Sir Hans Sloane, founder of the Cadogan Estate, holds court. The Bupa Garden, designed by Cleve West, recognises the therapeutic effects of green spaces and has a soothing water feature at its centre (the whole garden will be relocated to a care home after the show). Andy Sturgeon has four pools in his Cancer Research UK Garden. Sweet promises: “Water will cascade, pour and slide. It will be wonderful.” It will also, surprisingly, be environmentally friendly. Chelsea is to gardens what Paris is to clothes. It sets trends. If every one of the 157,000 visitors (this number is capped) went back to the shires and fitted water features, Britain would soon be a desert island.

“All water comes from our own on-site bore hole,” Sweet says. “We recycle 75 per cent of it.” But what if you don't have your own bore hole? “Gardeners have been collecting rainwater for ages and we're finding ever more ingenious ways. We're showcasing lots of devices this year for capturing and recycling water from traditional water butts to more elaborate grey water schemes. It's all very do-able.”

Water bubbles up in the Chelsea debut of Pip Probert. “I am very nervous,” says the 24-year-old designer, despite winning gold at Tatton, the other big RHS show. “I've been planning for well over a year, but so much can still go wrong. We have a green roof and it was supposed to be alliums but they just haven't worked so we've gone for armerias instead.”

Green Living is a 5m by 5m plot. “Our homes are getting smaller and smaller,” says Probert. “So this garden is a multifunctional outdoor room for working and playing. It's not for granny to potter about in. I try to use contemporary materials and trends from interior design to create a unified interior and exterior.” From Marshalls, the show's sponsor, she has sourced light stone flooring that would be at home in a kitchen. There is no concrete. The walls, like the roof, are green: “I was inspired by Patrick Blanc and am using grasses, like ophiopogum, and lavenders and heucheras.” And, yes, water: six bubbling towers lit from inside. “They'll be like light sabers and the noise is designed to drown out city sound pollution.”

Purple is big in Probert's garden and has dominated Chelsea for the past few years. “Purple and blue show no signs of going away although there is more pink this year,” says Sweet. “One of the colour trendsetters is Tom Stuart-Smith, so watch his Laurent-Perrier garden.”

Sales of veggie seeds continue to outgrow flowers. Allotments, once left to the weeds, have now sprouted waiting lists. Our appetite for organic food is unending. So it's no surprise there is also a big foodie element. “Home-grown fruit and veg tastes better and you know exactly where it's come from,” Sweet says. “It's the foodiest Chelsea in a long time.”

Daylesford Organic has created an organic agrarian garden. And, if it does rain again, you can always shelter over a cuppa with Diarmuid Gavin in his Café Garden.

RHS Chelsea Flower Show: May 20-24. RHS members only May 20-21.

Tickets: rhs.org.uk/chelsea or call 0870 8422234. Prices range from £15 to £46. Tickets must be bought in advance.

Trend setters

Blues and purples continue to dominate, with pink coming through. If you have space, try violet-blue Buddleja Davidii Empire/Nahno Blue. Rosmarinus “Blue Rain” trails brightly from hanging baskets. Transform a dull wall with Clematis Zobluepi Blue Pirouette. (All from £3.80 to £7.80 at jacksonsnurseries.co.uk).

Create an instant vegetable patch with the Instant Organic Salad Garden, 11 sets of established seedlings including rocket, mizuna and spinach (£36.99, crocus.co.uk). Combine self-sufficiency with Chelsea's key colour - purple - and try Asparagus Pacific Purple (£4.95 from crocus) or Trionfo Violetto climbing French beans (£1.59 from gonegardening.com ).

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