The clipping starts when plants are young, so it takes many years before the proper effect is achieved.

It is also labour-intensive, which is why such topiary is only occasionally seen in Hong Kong's parks.

In China, topiary is generally more temporary and is created by assembling a metal framework, covering it with an appropriately-shaped wire mesh and then packing it with soil and planting thousands of very small growing plants.

This style of topiary has an advantage in that it can be erected for special occasions and at exhibitions.

Harbin is the site of a particularly impressive display of birds, pandas and other decorative art.

The China Flower Association has sent a team of eight, including nurserymen from Sichuan, to Hong Kong to construct the butterflies. They will be helped by local labourers.

Construction is time-consuming. The topiary is 2.5 metres high, weighs more than 1,000 kilograms and involves 30,000 small flowers which must be individually planted.

The three main flowers which have been used are alternanthera versicolour, which provides the red colour, alternanthera bettzickiana aurea mana for yellow and echeveria for white.

However, a total of nine plants will be incorporated in the butterflies and the decorative base.

Regional Services Department manager Wong Wing-kong said any fine-textured plant would work, although the three main plants used in the butterflies were the most popular.

'As well as colour and texture, the plants must be tough and fast growing,' he said.

'It does not take a specialist to create the topiary but you need to be skilled to trim it and keep the plant alive.' Mr Wong said the butterflies would be watered once during the show with a mist blower.

The plants, which took about two months to mature, were grown in Hong Kong from tip cuttings.

'The Urban and Regional Services departments grew the plants this way because temperature control is very important,' said Tai Po District amenities officer Chow Chi-man.

'It is very cold in Jilin [home of the China Flower Association] and to raise the plants there would be expensive.

'We planted 20 per cent more plants than needed but the extra ones will not be wasted: they will be used in parks.' This is the third time topiary has been shown at a Hong Kong flower show.

But with constant pressure on the organisers to find something new each year, Mr Chow said there was no guarantee it would be on display next year.