The Alternative Flower Show

The Royal Horticultural Society's annual gardening extravaganza opens next week. But you don't have to go to Chelsea to find original ideas. Terry Kirby and Rebekah Curtis report

1 The guerrilla gardener

Richard Reynolds began what he believes is a revolution in the urban jungle of Britain's cities. In September 2004, the freelance advertising planner and keen gardener saw that some of the flower beds and tubs in public spaces near his home in the Elephant and Castle area of south London seemed a bit neglected. Armed with tools, some compost and a few cheap plants, he set forth one night to turn these sad, litter-strewn spots into green oases.

Mr Reynolds now has a dozen different sites which he maintains and plants, a growing army of volunteer helpers and a big ambition: "I want to see 100 recorded instances of guerrilla gardening across four continents by 1 September this year.'' Dozens of people have contacted him to say they too have been guerrilla gardening, sowing seeds and plants up and down the UK.

He said: "I did get the police come along when someone said I was stealing plants - I showed them the dandelions I was uprooting and they just laughed and drove away.''

Southwark council also takes a relaxed attitude: "I entered the local Greening Southwark competition with one of their flower beds I had planted. I got a very nice certificate.''

2 The Lavender Hill mob

Today, it is simply the sprawling outer surburbs of London. But once, the area around Carshalton and Sutton was known as the lavender capital of the world, helping to make the fortunes of perfume companies such as Yardley.

In the mid-1990s, Yardley agreed to help fund a project to reclaim neglected allotments in Carshalton. The scheme was devised by a local environmental group and inmates from the nearby prison, HMP Downview, helped clear rubbish from the site and grow lavender seedlings from traditional local varieties before planting them out.

Today, Carshalton Lavender is a huge success. Each year, local people are encouraged to help harvest the crop over a weekend in late July. They are able to take away as much as they want; the remainder is made into lavender oil, which is sold locally and at farmers' markets. Much of the harvest is carried out using a special harvester made from recycled machines. The project is now run by a local voluntary group, whose spokeswoman, Kathleen Claridge says: "Everyone around here says how much they enjoy the scent in summer.''

3 The red-hot chili peppers

West Dean is the archetypal English country house, nestling in the South Downs, near Chichester in Sussex. Its tranquil glasshouses, walled gardens and arboretum surround a charitably funded college, which offers courses in music, the arts, conservation and restoration. Obviously the kind of place to find a celebration of that most un-English of plants: the chilli.

West Dean's Chilli Fiesta, held each August, attracts thousands of visitors and features around 250 types of chillies and sweet peppers, exhibited in the restored Victorian glasshouses, and bearing names like "Apache" and "Wild Fire". There are dozens of stalls, demonstrations of chilli-based cuisines from Thailand, India, Mexico and the Caribbean and the opportunity to taste chilli ice cream and chilli chocolate to the accompaniment of live Latin music.

4 The railway gardener

An artist and illustrator in south London, Lucy Hughes admits to scattering wildflower seeds with abandon, like a fairy spreading magic dust. A particular target for her attentions has been the railway station at Hither Green near her home. "There is some waste ground by the side of the platforms where people just threw empty crisp packets and stuff. So I started scattering seeds and now there are daisies and other plants.''

Originally from North Wales, she began to wild-garden in London when she missed the hedgerows of her youth. She now scatters seeds around any spare ground she comes across. " If people see things growing, they tend to respect these spaces a lot more and stop fly tipping and begin to look after them. Some of the places I've sowed seeds have been taken up and preserved by councils as conservation areas.''

5 Redwood Ron

Most people might expect to have to wait a few years to see a tree they have planted grow into maturity. Ron Levy knows he will never see his reach anything like their full size. He would have to be around in 2,000 years' time - the lifespan of the average redwood tree.

To say Mr Levy, a 45-year-old computer programmer, is obsessed with redwoods is probably an understatement. He plants them in discreet locations, mostly in Essex where he lives. He also travels the country, documenting redwoods for his website, (redwoodworld.co.uk).

The redwood, one of the most ancient varieties of fir, is native only to the United States, but many have been planted in Britain by landowners, gardeners and local authorities. Mr Levy rejects the suggestion that it is wrong to plant non-native species, arguing there is no danger of them dominating the landscape because they do not re-seed easily. "I'm not a natural tree-hugger, I just fell in love with them," he says. "They have this amazing prehistoric quality and wonderful soft bark."

6 The sky gardens

Once upon a time, roof maintenance meant replacing tiles. But for many eco-conscious house owners and builders, green roofs are a way of encouraging biodiversity and preventing flooding. Oh, and they look rather good too.

In Sheffield, they are used on bus stops and a primary school. In Wallington, Surrey, the Beddington Zero Energy Community (BedZED), a development by the Peabody Trust in partnership with environmental consultants, the Bio-Regional Development Group, has constructed green roofs on what claims to be Britain's largest carbon-neutral eco-community.

BedZED is a high-density development, designed to minimise urban sprawl and protect greenbelts. Like many green roofs, those at BedZED are planted with sedum - a low-maintenance succulent. "Green roofs prevent flooding by absorbing rain rather than letting it run directly on to concreted streets, and overwhelming the drains,'' explains Jennie Organ, spokeswoman forBioRegional.

7 The poison garden

Visit any public garden and you'll usually find a sign somewhere that says: "Do Not Touch" or "Keep off the Grass". On the gates of the Poison Garden at Alnwick Castle, a sign says simply: "These Plants Can Kill."

Part of the family estate being restored by the Duchess of Northumberland, the Alnwick gardens have a special licence from the Home Office allowing them to grow plants with poisonous or narcotic qualities which are normally illegal to cultivate.

Varieties of deadly nightshade, or belladonna - one of the most toxic plants in the world - grows alongside the coca plant (used to make cocaine), opium poppies and magic mushrooms. There is also wolfsbane or monk's hood, the plant associated with werewolves. But of all the plants, the one that kills the most is, of course, tobacco.

"We've had a few people trying to take cannabis leaves, but they didn't manage," says Alison Hamer, the garden's learning and development manager So is it possible accidentally to ingest some lethal or hallucinogenic substance? "The garden is well-policed by our wardens and the most dangerous plants are behind cages."

8 The Chelsea flower show

Katie Gower will be able to see the crowds milling around the Chelsea show ground next week from the shade of an olive tree on her roof garden, perched among the chimney stacks of the Peabody Trust's Ebury estate.

The 150sq ft plot is crammed with choice specimens, including grapevines, orange trees, cordylines, agaves, palms, honeysuckle and lavender. Like the expensive Chelsea show gardens across the road, it has proved inspirational: six neighbours now have gardens in bloom among the rooftops.

Mrs Gower, 59, who has spent 24 years creating her horticultural haven with her husband David, says: "Several neighbours got keen after I started. The garden gives them pleasure. We're up there every evening or in the early morning. We all meet up and exchange cuttings. It's a good little community."

The Gowers also maintain the garden in the block's communal courtyard. "It's for the benefit of all our neighbours. London is such a cold and unfriendly place that we're trying to keep a communal spirit going," says Mrs Gower.