Over the years, many theories have popped up to attempt to explain why spending time in green space can reduce feelings of stress and anxiety, improve self-image and, in some studies, even measurably reduce the need for pain medication. From their purported ability to clean the air, to allegedly mood-lifting compounds emitted by soil bacteria, to some mysterious effect that simply seeing the colour green has on our brains, let’s look at how the evidence stacks up.
Probably the most common claim I see is that plants, particularly houseplants, clean the air. While they do indeed do this on a planetary scale, the latest research now suggests that in indoor spaces the sheer volume you would need to achieve this makes it implausible. Quite how many? Well, several hundred per square metre of living space to achieve the same benefit of simply opening a window. Even I can’t cope with that.
Another one of the most enduring memes on social media is that soil bacteria, inhaled into our bloodstream, has been proven to improve our mood. Intrigued, I went to track down the scientific paper. This was a single study where the bacteria were injected directly into the brains of live lab mice. Unless you’re a caged mouse, this experiment doesn’t really confirm very much and even then the method of administration doesn’t sound like much fun.
What we do know, however, is there is something unusual about the colour green that seems to affect how our brains function. Researchers investigating the effect of exercise on mental health have found that seeing views of the natural world projected on to screens had additional benefits over and above the workout alone. However, when they manipulated the colour of these screens to show the same views in black and white or in shades of red, the effect was markedly reduced compared to the original green. This may mean that using evergreen species or, potentially, even something as simple as painting your fence green might contribute to its effect.
Similarly, designing your garden to be higher maintenance so that it is not simply somewhere to sunbathe in summer may improve the beneficial effect by encouraging gentle workouts. We know that low-impact, prolonged exercise, such as gardening, can burn more calories than a hard-hitting gym session, despite feeling easier. It is a way of being active that may appeal to far more people – if for no other reason than it’s being outside in the fresh air and isn’t as brain-numbingly boring as looking at the flashing lights of the treadmill, which brings me to my final point…
Gardening is also a classic form of practising mindfulness, which can help to focus our thoughts on the here and now, distracting us from any worries or stresses. It’s not my thing, but mindfulness exercises are well documented to have a positive impact on mental health, and are even recommended by the NHS. So ditch dull, low-maintenance schemes such as herbaceous plants for a more absorbing design with a backbone of evergreens, and you could turn your garden into a welcoming, therapeutic space.
Follow James on Twitter @Botanygeek