Dutch King Willem-Alexander, Queen Maxima, Princess Laurentien and Prince Constantijn (L to R) wave to people on the balcony of Noordeinde Palace in The Hague, the Netherlands, Sept. 17, 2019, on "Prinsjesdag", the Prince's Day. The Prince's Day is held every year in The Hague on the third Tuesday of September, which marks the opening of the parliamentary year. (Photo: Sylvia Lederer/Xinhua)

Dutch King Willem-Alexander on Wednesday opened the gates to one of Europe's largest gardening fairs, a once-in-a-decade show focusing 2022 on how to make cities greener.

But critics have denounced the show, which features displays by 200 participants from 25 countries, as a "money pit" that has massively overrun its budget.

The Floriade 2022 exposition, which runs until early October, is expected to draw more than 2 million enthusiasts to the central city of Almere.

The Floriade 2022 shows "what a green city could be like in the future... what kind of materials could be used for this and what role the horticultural sector could play in it," said its curator, Annemarie Jorritsma, a former mayor of the city.

Each decade, a different Dutch city gets to host the gardening extravaganza. Almere, the latest, is a city that was itself created by the Dutch by draining part of the former Zuiderzee bay to reclaim land.

As well as being a showcase for Dutch horticulture, each participating country has its own pavilion. China's is showing "new ways of using bamboo," said Jorritsma. Italy is focusing on permaculture, while France shows how metallic imitations of trees can be used to cool cities.

The German pavilion is decorated with plants including garden plants, trees, food crops and wildflowers to form a "living ecosystem whose appearance would change throughout the exhibition," organizers said.

The event has however been criticized for budget overruns that threatened its very existence. Dutch media have reported that Almere has significantly overrun its 10 million euro ($10.8 million) budget for the project.

AFP