Giving people access to the natural environment could yield important benefits for the "mental capital" of a city.

Green urbanism - the practice of creating communities beneficial to humans and the environment - is an important element of a liveable city. Trees improve air quality, reduce cooling and heating energy use, and make urban environments a pleasure to behold.

Parks allow people to gain a fresh perspective on life, helping visitors to temporarily escape from buildings and crowded streets. Trees and grass in common spaces improve social interaction. Moreover, parks and greenery, such as New York's Central Park and Singapore's Botanic Gardens, soften the tone of a built landscape and make high-density urban environments more liveable.

Contact with nature improves the physical and mental health of individuals and communities. Physical activity during gardening, for instance, reduces stress, anxiety and depression.

Natural environments could even improve attention and memory. One study has shown that hospital patients who were able to look out at trees and nature from windows recover more quickly from surgery than those whose views were restricted to buildings.

There is growing interest and research on horticultural therapy - which taps nature's benefits for human health.

It involves a planned programme where trained professionals use plants as a therapeutic medium.

Horticultural therapy is well established around the world and, in some countries, it has been introduced in educational institutions including kindergartens and special-needs schools. It is well accepted in medical care facilities, especially in rehabilitation hospitals, psychiatric services, palliative care and aged homes as a means of providing patients with graded and carefully designed gardening activities to improve their quality of life. Such therapy has also been noted to promote social functioning and self-esteem in patients with psychiatric conditions.

Psychologist S. Kaplan suggests that nature has specific restorative effects on the brain's executive attention system. Focusing on technology and multitasking places demands on executive attention, and interaction with the natural environment is particularly effective in replenishing the brain's depleted resources, he believes. This may explain the improved mental status of busy city-dwellers who spend some time at the parks or gardens.

To ensure Singapore is a pleasant city to live in, visit or do business, about 9 per cent of land here has been allocated for parks and nature reserves.

And about 85 per cent of residents will live within 400m of a park by 2030. The proposed Round Island Route, stretching 150km, will provide an uninterrupted leisure route around the island, linking major cultural and historical sites and cycling networks.

Singapore has a master plan for a clean, green and blue sustainable city and is making a paradigm shift from a "Garden City" to a "City in a Garden".

There will be roads with complete canopy cover and heritage tree programmes, and green connections across the city.

Building technologies for a green city and capabilities to fulfil sustainable development are important. Urban agriculture includes orchards for harvesting fruits and crops growing at different scales, from large plots to small rooftop gardens and lawn spaces around residential estates.

Urban agriculture is now a growing interest and provides fresh food at a low cost to local supermarkets, while integrating composting facilities to recycle household organic waste. Many private enterprises have seized these opportunities with government support to establish new start-ups which can potentially be expanded to other Asian cities. The increased greenery also increases energy efficiency in buildings.

Many organisations work together to enhance the city sustainability and liveability in the island's dense urban environment. Singapore now has about 72ha of rooftop greenery - the size of over 100 football fields.

Contributing to this landscape are buildings, including hotels and hospitals, which retrofit greenery on their roofs and walls, and new developments that incorporate greenery in the building designs.

The National Parks Board conducts scientific research on plants, trees, insects, birds and human-nature interaction. There is a keen interest now on the health benefits of nature and its impact on the mental health of the elderly.

In one trial here, conducted with the Department of Psychological Medicine at the National University Health System, elderly participants planted vegetables such as lady's fingers and learnt gardening techniques like composting and transplanting. When the crops were ready for harvest, they cooked them together. They also had guided visits to the Singapore Botanic Gardens, Sungei Buloh Wetland Reserve and Gardens by the Bay.

In preliminary results after three months, the elderly on horticultural therapy did better than a control group in scores for life satisfaction, memory and psychological well-being. In addition, it was found that cytokine interleukin-6 (IL-6), a pro-inflammatory protein, which lowers the body's immune system, showed significant reduction in the horticultural therapy group, compared to the control group.

The outcomes of this study provide empirical evidence for the effectiveness of horticultural therapy in improving the psychosocial and cognitive well-being of the elderly.

Besides improving the environment by way of air purification and noise filtering, natural areas are of crucial importance for the liveability of modern cities and the well-being of residents.

Some cities, including Singapore, are incorporating benefits of the green environment into urban design as important aspects of city planning that may influence mental health and even cognitive function. Spin-offs for "economic" health arising from the natural environment include the capacity for parks and gardens to improve the productivity of workers. The mental health benefits of nature can be incorporated into a wide array of initiatives and investments in sustainable cities.

Growing the green movement is not just the responsibility of city planners and politicians, but also the community. For some mental health professionals, being volunteers in the planning of a therapeutic garden at HortPark off Alexandra Road provided them with a platform to connect with the public on issues concerning ageing and mental health. At regular workshops, psychiatrists and nurses give talks on depression, anxiety and dementia to educate the public and to de-stigmatise mental illness. This project is part of the Dementia Prevention Programme which has been successfully conducted in Jurong, Queenstown and Eunos.

Ageing-in-place, a popular catchphrase in Singapore, is possible if we begin to invest not only in social infrastructure but also green urbanism, which will certainly benefit our mental health.

•This article was adapted from a chapter in a new book, Mental Health And Illness In Cities.