Dutch Floriade is a once-in-ten-year extravaganza that's in full bloom again this year. Running for seven months until October, it's a colourful and colossal phenomenon with wonders at every turn, writes Harvey Grennan.

The Dutch take their flowers seriously. The Aalsmeer flower auction near Amsterdam is the world's biggest, covering a million square metres and selling 20 million flowers a day which are air-freighted around the world. Holland provides half the world's cut flowers with exports worth $11.5 billion a year.

Every year the famous Keukenhof gardens at Lisse near The Hague attract nearly 900,000 visitors and 10,000 buses to the annual display of tulips. This is no ordinary garden - seven million bulbs are planted every year to form the most amazing mosaics of colour.

But the real "biggie" in terms of visitors is the Floriade World Horticultural Expo which is held at a different location only every 10 years, this year from April to October at Venlo near the border with Germany. It attracts 10,000 visitors a day - two million over the period of the expo.

This is the showcase of the country's horticulture industry, a major driver of the Dutch economy. Oddly, figures are not divulged but - for just a single event - tens of millions of dollars are spent on infrastructure, tens more on buildings and landscaping and tens again on exhibits.

Floriade is divided into five areas over 40 hectares separated by natural forest, each with its own theme - education and innovation, an international showcase (ranging from the superb Chinese and Indonesian pavilions to some tacky souvenir bazaars), lifestyle, sustainability and green industry.

A few statistics: 1.8 million bulbs, 190,000 perennials, 18,000 shrubs, 15,000 hedge plants, 5000 rose bushes and 3000 trees have been planted for the occasion. In addition, there are swathes of existing woodland plus many thousands of exhibitor plants appearing in the designer landscapes featuring man-made lakes, waterfalls and waterways.

The two main buildings are architecturally stunning - the Innovatoren through which visitors enter and a huge glass pavilion, the Villa Flora. The first will be retained in a planned "green" industrial park as a research incubator for the agri-sector and the other as an exhibition centre.

The show's highlights are the Villa Flora - the largest indoor flower exhibition in Europe - which demonstrates the staggering array of products offered by the industry from huge palm and bamboo trees to multifarious species of delicate orchids, and the Tropical Treasures heated glasshouse of equally huge tropical plants from Mexico to Africa.

My Green World is an egg-shaped pavilion revealing the future of sustainable food production - an algae reactor to feed plants, roof gardens, growing plants in the dark under red LED lighting, and hydroponics.

Great use is made of digital audio-visual technology, most particularly in the Kids' University where children can drive a tractor simulator, play interactive educational games, learn to cook and taste new vegetables.

The cleverest display, if not the most spectacular, is a "sushi train" where visitors sit at a counter and pick off moving trays on which sit symbols of agriculture….perhaps a milk jug or an egg. Place the tray on a recess in the counter and a screen provides a first-hand account of the story of that particular farmer in several languages.

There is a continuous program of cultural and arts events extending into the summer evenings from African musicians and brass bands to pop and classical performances, light shows and street theatre. Most spectacular are the Close Act stilt dancers in extraordinary butterfly costumes.