It's notorious for its cramped living conditions, traffic-clogged streets and polluted air, but once a year Hong Kong celebrates all things green at the city's flower show.

Though most residents have no outdoor space for gardening, thousands flock to the annual 10-day event, which started on Friday and covers six football pitches in the central Victoria Park.

In contrast to the surrounding apartment and office blocks, the park has been overtaken by cascades of orchids -- the show's theme flower -- along with tulips and kitsch floral sculptures, from giant ants to pandas and toadstools.

Some visitors come just to photograph the lavish displays, but many are picking up plants and gardening equipment. The park is lined with stalls selling seeds, pot plants, compost and garden tools.

It's a testament to the fact that, despite Hong Kong's cheek-by-jowl and high-rise lifestyle, its residents crave greenery and are making the most of the limited space they have to grow plants.

Queenie Wong, 25, who is studying Chinese medicine at Hong Kong Baptist University, holds a tiny fern in a pot, which she has just bought from one of the stalls.

"I don't grow anything at home because I don't have the space. I'll take care of this plant in my university office, which is where I spend most of my time," she says.

Like many in Hong Kong, 11-year-old Zoe Shum makes do with a balcony at home for her horticultural ambitions.

"I grow bamboos on a balcony, but I wish I had more garden space to grow more things. At school we have lots of plants and they're really pretty," she said.

For 30-year-old Amy Tang, the show is a chance for her parents to stock up.

"I bring my parents here every year because they like to shop for plants for their balcony -- and we like just looking at the flowers," she said.

Hong Kong's popular image is of a frenetic commercial hub where making a fast buck trumps all other concerns, but flower show chairman Horace Cheung says its seven million people do enjoy connecting with nature.

"We may be a busy, densely populated city but there is increasing awareness of how planting and growing things can enrich the environment and our lives," he told AFP.

Small plots for vegetables and flowers, made available to residents as part of the government's community garden scheme, are heavily oversubscribed, says Cheung.

"We have to have a ballot for plots every time they come up because of the demand," he said.

Residents pay HK$400 ($51) to do a gardening course which includes working on a 2.25 square metre plot for four months. The year 2011-12 saw more than 10,600 participants across 21 gardens, according to the Leisure and Cultural Services Department, which also runs the flower show.

The event was launched in 1968. Organisers expect around 500,000 visitors at this year's show, which features a series of gardening talks and an information stall to promote sustainable living -- another contrast in a city where avid consumption often outpaces environmental concerns.

Joseph Leung, an executive director at Hong Kong theme park Ocean Park, is promoting its vibrant stand at the show, which includes edible plants, recycled containers and an aquaponics section on how plants can grow without soil.

He believes Hong Kong residents are indeed concerned about their environment and want to simplify their lives.

"People are more interested in sustainable living. I think they have got to a point where they are so busy that they want to stop and go back to basics," he said.

"When it comes to improving our environment we have to start somewhere -- we have to start at home."