EVERY month in my column, I look into a claim that is ubiquitous in the media, exploring the often surprisingly shaky foundations behind long-held positions we take for granted. This month, though, I wanted to set myself the challenge of examining the evidence behind one of my own closest held beliefs, to see how hard it can be to be objective.
As someone who not only shares his tiny flat with an ever-expanding collection of 500 houseplants, but who also makes a living from writing and presenting about plants, I am perhaps unsurprisingly deeply invested in the idea that being around them improves our mental well-being. However, what does the science actually say about this?
Advertisement
Probably the most common paper cited in lifestyle and gardening magazines as evidence for the beneficial effect of houseplants is a study conducted at a Pennsylvania hospital involving . Researchers found that those in wards with windows onto a green view experienced a 12.5 per cent shorter hospital stay and needed less pain medication compared with those looking out on a brick wall. Perhaps even more intriguingly, the nurses鈥� notes about the patients鈥� mental well-being revealed that those with a green view were 80 per cent less likely to show signs of emotional distress.
But what most press stories don鈥檛 report is that this study was conducted way back in 1984. Examining its design raises other questions. Rather than a gold-standard clinical trial, where relatively large groups of participants are rigorously selected and then meticulously subjected to different interventions, this study was based on simply retrospectively looking at hospital records and involved just 46 patients, spread over a nine-year period, none of whom the researchers ever even met. They are potentially interesting results nonetheless, but hardly something to hang such bold claims on decades later.
In science, the sign of a solid hypothesis is reproducibility. Do the same experiment multiple times and you should expect similar results. So when a 2009 experiment, using double the sample size, found that people recovering from similar minor surgery also reported 鈥渟ignificantly more positive physiologic responses evidenced by lower systolic blood pressure, and lower ratings of pain, anxiety, and fatigue鈥� when provided with plants in their rooms, these were some of the first suggestions that this . In recent years, a range of similar (although admittedly small) studies on different groups and by different teams have repeatedly reported similar results.
Thankfully, most of us aren鈥檛 recovering from surgery. Can a view of green plants indoors help the healthy too? Well, a range of exercise studies have demonstrated that if you put a bunch of blokes on treadmills, those shown natural views on screens perceive the workout as being less intense and report having higher feelings of self-worth Take the exact same view and manipulate the colours to make it red or monochrome, however, and the impact appears to be diminished.
鈥淚f you put a bunch of blokes on treadmills, those shown natural views on screens perceive the workout as being less intense鈥�
The problem with some of these studies, though, is that the views don鈥檛 involve living plant material, just screens. Real-life plants add a range of variables that can affect the results, including everything from altering the composition of the air to changing how people navigate through indoor spaces.
Even studies that use actual plants might be highly dependent on the species chosen. With about 400,000 to select from, this could well affect the result. After all, loads of plants have red leaves, for example, and we have already explored how digitally changing plant-filled views from green to red appeared to reduce the therapeutic impact. Could simply painting a room green have an effect similar to, or potentially even greater than, the presence of actual plants? If we were to set up such an experiment, how would we even measure the impact on mental well-being, which is a question plagued by subjectivity?
Therein lies the inherent issue with testing this hypothesis: there are just too many variables. Given this, I am the first to admit that my belief in plants鈥� therapeutic power is based as much on subjective, anecdotal experience as it is on solid scientific data. But I probably speak for all gardeners when I say that this really isn鈥檛 a deal-breaker for me. When it comes to answering the philosophical question of whether plants make me happy, my own fuzzy experience is just as relevant as any rigorous study. Moral of the story? It turns out it is indeed very hard to be objective.
