There may be another reason why the garden is Noor’s “happy place” – Mycobacterium vaccae, a microbe naturally present in soil, which is thought to have antidepressant qualities.

A study on an experimental treatment for lung cancer, conducted by oncologist Dr Mary O’Brien at The Royal Marsden Hospital in London, noted that lung cancer patients who had been injected with the bacterium reported feeling happier and expressed more vitality and better cognitive functioning.

O’Brien’s research concluded that, when added to standard cancer chemotherapy, the common, harmless bacterium significantly improved the patients’ quality of life without affecting overall survival times. The study was published in 2002 in the journal Clinical Oncology.

Another British study, published in 2007 in the journal Neuroscience, tested Mycobacterium vaccae on laboratory mice. The researchers found that the bacterium activated the animals’ brain cells to produce serotonin and altered the mice’s behaviour in a way similar to that of antidepressants. Serotonin is a neurotransmitter that is said to stabilise mood and boost feelings of well-being; a lack of it has been linked to an increased risk of anxiety, depression and irritability.

Mycobacterium vaccae in soil is thought to enter the body in various ways – through inhalation when gardeners are outdoors, through physical contact with the dirt, or through a cut on the skin. According to another experiment, also done on laboratory mice, the bacterium’s natural antidepressant effects can be felt for up to three weeks. The findings from this study were shared at the annual meeting of the American Society for Microbiology in 2010.

If you doubt that gardeners are a happy bunch, consider a survey by Gardeners’ World magazine in 2013 that found that 80 per cent of gardeners reported being “happy” and “satisfied” with their lives, compared to 67 per cent of non-gardeners. Another survey, by researchers at the University of Texas and Texas A&M, asked nearly 300 older adults how they would rate their “zest for life” and levels of optimism – the gardeners scored significantly higher than the non-gardeners.

Katie Vajda, a 42-year-old artist and photographer who lives in Hong Kong’s so-called “back garden”, Sai Kung, has a small patch in which she grows edible plants such as chilli, parsley and mint, and flowering plants including hydrangea, daylily and bougainvillea. She agrees that the tactile aspect of gardening contributes a great deal to her positive and relaxed nature.

“Gardening is a healthy pursuit in so many ways because it allows us to slow down, reconnects us with the earth and boosts our mood,” says Vajda, who grew up on a farm in Australia and developed an interest in gardening after watching her mother and grandmother tend to their gardens.

“When I studied fine arts here in Hong Kong, I did ceramics for a year. It was one of my favourite subjects because it involved handling clay. Working with a natural material like clay, which is not dissimilar to soil and water, was almost therapeutic. We recently started a communal composting initiative in our village, which is pretty exciting – by turning our green waste into compost we are creating even more nutrient-rich soil to get our hands into.”

But how can you benefit from the happiness-inducing effects of soil if you do not have land of your own? Community and allotment gardens are excellent places to work with dirt while honing your gardening skills.

In the last several years, space-starved concrete jungles like Hong Kong and Singapore have witnessed a rise in the number of such gardens. In Singapore, residents can register for the 1,000-or-so plots in allotment gardens in various national parks, such as HortPark, Pasir Ris Park and Yishun Park. Each allotment gardening plot features a 2.5m x 1m raised planter bed and costs S$57 (US$42) a year to lease.

Rooftop Republic, a social enterprise that promotes urban farming and sustainable living in Hong Kong by way of urban farm set-ups, activities and events, offers regular interactive workshops during which participants of all ages and levels of experience can get their hands dirty while learning to grow their own vegetables. Its Garage Greens Urban Farming Experiences workshop, which is held every first Saturday of the month (until June), teaches attendees how to germinate seeds, transplant seedlings and fertilise plants.

Organic farming group Permaclub, situated in a valley in Clear Water Bay, encourages community gardening, and connects Hongkongers who want to grow their own fresh produce, pick up hands-on skills such as composting and seed saving, and more.

Change your life: smile with Dr Happy’s positive psychology and lift your well-being

Noor lives in a landed property, but she does not have much ground outside to work with. This, she says, is where pots and planters come in handy. If you live in a flat, she suggests dedicating small spaces in your home – such as the windowsill or balcony – to growing indoor plants, herbs and vegetables in containers. A vertical garden might be more practical for someone living in a flat.

“The size or type of garden does not matter,” says Noor. “As long as you have the chance to handle the soil, make the effort to really nurture your plants, and allow yourself to be fully engaged with every aspect of keeping those plants healthy and flourishing, you are bound to notice a positive shift in your mood in time. You may even catch yourself smiling while you’re gardening.”