When Dirk Cools founded the Solitair tree nursery with the aim of growing mature trees that would be ready for sale not five or 10 but 30 years hence, his friends were not convinced it was a smart business move.

That was in 1986 and, happily for Dirk, the world has caught up. Today the 20-strong family-run company enjoys a flourishing market for the trees he has painstakingly raised over decades. The Belgian nursery, 30km northeast of Antwerp, now comprises a square kilometre of 60,000 shrubs and trees.

“I’ve always been interested in how, out of a big field of trees, a couple of them could grow differently,” says Dirk. “So when I started I decided to keep the nicest ones and let them grow bigger.”

As his original collection matures, the trees are lifted and exported all over Europe. The nursery serves a burgeoning list of city governments from London to Tbilisi that want to bring a bit of the wild to their urban landscapes.

Loading the trees for journeys that can take several weeks is only the last stage in the “lifting” process that begins years earlier. Solitair’s team trims the trees’ roots every two or three years using a machine that slices under the root-ball like a bladed ice-cream scoop, making them easier to lift when the time comes. The trees, which can weigh up to four tonnes, are then wrapped in protective nets and laid on lorries.

“For a while people wanted nature at a distance,” says Dirk’s daughter – and Solitair employee – Chloë. “Now people want the wild back. In crowded cities the opportunity to find solitude under a large tree is increasingly special.”

With a move away from civic spaces populated with whippet-thin specimens, city delegates now travel from afar to visit Solitair. Their mission is to find “character” trees that will provide shade, shelter and aesthetic charm. “People are clearly choosing natural trees,” says Dirk. “Their individuality can have a big impact on a city’s atmosphere.”

Downtown Bangkok is choked with traffic. Horns beep frantically at motorbikes snaking through the smoke plumes that pour from ageing cabs and open drains leak unsavoury smells in the baking heat. Regional growth is pumping wealth into a capital whose heart beats with optimistic vigour but the hangover from recent rough-and-ready history remains.

Rapid development fills the city with contradictions: gleaming malls shadow slum streets and well-heeled businessmen haggle with street-food sellers below gleaming office towers. It is a place of industry and tradition but not a city where you would expect to stumble upon a lush forest. Yet venturing through Prawet, an industrial quarter in Bangkok’s southeast, that’s precisely what you’ll find.

Even more surprising is seeing the name of oil-and-gas company PTT hanging above the entranceway to the freshly opened manmade Metro Forest. While the sharp minds at Bangkok’s city hall are busy fixing transport and sanitation issues, it seems private companies are also doing their bit to improve the city’s liveability.

Pailin Chuchotthaworn, the CEO at the helm of PTT, believes building a better Bangkok is a corporate responsibility. “We are 84th in Fortune’s Global 500 companies, so there isn’t any other company comparable to PTT in Thailand,” says the chief of the public-private company. “That ranking means that we need to be a role model for many other large corporations so they can follow in our footsteps and maybe do things even better in the future.”

Part of that process for PTT lies in its 19,000 sq m Metro Forest, which has sprung from the ground in just three years thanks to revolutionary horticultural innovation. Managed by Landscape Architects of Bangkok (LAB), the project uses a technique developed in Japan by Dr Miyazaki Wagyu to quickly propagate a natural ecosystem. Dr Sirin Kaewlaierd helped LAB select about 300 species of local flora, all of which now fight for survival in the densely planted forest. Spurred by the tropical climate, trees have quickly risen to reach the dramatic viewing platform that carves its way through the masterfully landscaped site.

“According to the theories of Dr Wagyu and Dr Kaewlaierd, the forest will mature in just 10 years,” says LAB managing director Tawatchai Kobkaikit.

It is an experience that already feels natural. As Monocle tours the site, birds are in full song and we’re warned to watch out for the snakes that are among the wildlife reclaiming the forest floor. The ground level is the preserve of scientists and researchers but the public can also enjoy the site from atop its 200-metre walkway and at the learning centre.

“More and more people are living in condominiums, even young children,” says Pailin. “If we can’t bring those people to the forest to appreciate it, we have to bring the forest to the city.”

Pailan doesn’t deny that PTT’s practices take from the earth and “create a lot of greenhouse gas” but he knows that, as Thai public awareness grows around climate change, his company’s green credentials must improve.

PTT’s next major project is the establishment of a game-changing university in nearby Rayong that will be centred on sustainability. Its urban forest will draw on lessons from Bangkok and, while Pailin believes his firm’s educational efforts are unrivalled in Thailand’s private sector, he is confident that other corporations will strive to match them.

Visitors to the Victor Civita Square on the west side of São Paulo are greeted by a wooden structure that forms a giant suspended walkway several feet above the ground. This is a green oasis in the heart of the city where families spend lazy Sunday afternoons, young Paulistas jog and work out (using the free gym equipment) and city-dwellers gather in the evenings for outdoor cinema screenings.

The architecture is not just strikingly innovative, it was also born out of necessity. For four decades this 13,000 sq m site housed a medical toxic-waste incinerator. The raised structure and its decked walkways now enable the citizens of western São Paulo to enjoy the park’s greenery without having direct contact with the contaminated soil beneath their feet. As such, the Praça Victor Civita stands as an excellent example to other city halls of what to do with unloved and commercially undesirable parts of their cities.

The square’s name itself hints at its somewhat unusual genesis. In the 1950s, Victor Civita founded Editora Abril, a firm that now publishes some of the most widely circulated magazines in the country. In 2008, the publishing house began a process that blossomed into a partnership with the São Paulo administration and paved the way for the creation of the space. “It is encouraging to know that the only square in town run by the private sector was built on really deteriorated land,” says Elisabeth Barboza, co-ordinator of the Friends of Victor Civita Square Association, in charge of the site’s management.

The square has also been responsible for transforming the surrounding neighbourhood: since it was opened seven years ago, property prices around it have increased by more than 300 per cent. “This is proof that the public and private sectors can work together for the benefit of the city,” says architect Adriana Levisky from Levisky Architects, who worked on the project in partnership with Anna Julia Dietzsch.

Abril has since taken a step back and the two main supporters of the square are now Sabesp, a water- and waste-management company, and CCR, a private group that manages highways, airports and subway systems.

The public-private model has worked here, not least because it has relied on the goodwill of private companies. “It is more than just wanting to have your company’s name attached to a sustainability initiative,” says Barboza. “It is about really having the feeling of contributing to a better city – a friendlier and more pleasant place in which to live.”

Inspired by the challenge of becoming the world’s greenest city by 2020, motivated Vancouverites are rolling up their sleeves – literally – to do their bit to beautify their neighbourhoods. The city’s boulevards, roundabouts and pavements would be dull were it not for the community associations and businesses that have mobilised to plant, prune and water public greenery across Vancouver.

The volunteer gardening project stems from a government initiative in 1994 with 15 plots in the Mount Pleasant neighbourhood but has since expanded to cover more than 350 spaces across the city. Under the scheme, residents are permitted to extend their gardens beyond their front yard. The well-cared-for and tastefully planted gardens that today flourish across the city are a reflection of the civic pride of the volunteers.

The government’s role is now largely administrative: green signs are posted on plots that can be taken on, while yellow signs indicate gardens that are already being tended to. An overview of guidelines and a recommended plant list are also available. But the rest is up to private citizens and the city’s 22 business associations who decide where, when and what they will be laying down.

In Strathcona, Vancouver’s oldest residential neighbourhood, the Business Improvement Association (BIA) has got together with its counterpart in neighbouring Hastings Crossing and with the Ray-Cam community co-operative for its street-beautification programme. “In an area like the Hastings corridor – which is a highly urbanised, largely concrete-and-asphalt commuter strip – adding more greenery makes it a more liveable and pleasant place to spend time in,” says Meg O’Shea, sustainability co-ordinator at the Strathcona BIA.

O’Shea organises youth landscaping on public lands and runs an urban tree nursery along Hastings Street, collaborating with businesses that agree to care for the young Pin Oak, Red Maple and Persian Ironwood saplings. She attributes the success of the scheme to Vancouverites’ love of the outdoors: “We have an extremely tight-knit community that cares a great deal. We are all working to make our neighbourhood a great place in which to live and work.”

Europe’s capitals are full of public parks that were once the lush private gardens of favoured aristocrats. Today the idea of a wealthy individual donating green space to their city seems fanciful but that is exactly what Bénédict Hentsch plans to do.

Bénédict, scion of Geneva’s oldest banking family (an ancestor even advised Napoleon), has designed and built a park with the specific intention of handing it over to the people of Geneva. “At first they thought I should be put into a museum – or a zoo,” he says, laughing.

This is the denouement of a convoluted story. The 30,000 sq m patch of land on the city’s western fringe has been through many incarnations. Originally a horseracing track, it was home to football club Servette’s stadium from 1930 thanks to Gustave (Bénédict’s grandfather), the erstwhile captain and goalkeeper. When the stadium fell into disrepair in the 1990s, Bénédict realised that it would need to be rebuilt across town. In order to convince city hall, he offered to turn the old site into a public park and gift it to the city.

Bénédict faced initial scepticism. “People thought it was unnatural to take three hectares and give it over to the city,” he says. But the creative director in charge of overseeing the park project says the city authorities didn’t count on Bénédict's loyalty to the people of Geneva: “He is not doing this as a banker but as a citizen.”

After 15 years of deliberation and construction, the park is finally nearing completion. Raised sides give the park a bowl shape, while the dominant central patch of grass is flanked by a children’s play area and a well-designed water feature.

On 28 June 2015, 85 years to the day since Bénédict’s grandmother inaugurated the football stadium that once stood here, her grandson will hand over his park to Geneva. “This city has given a lot to my family,” he says. “It’s only natural for me to want to give back. And at the end of the day, I don’t want to be the richest man in the cemetery.”