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Researchers have revealed the ideal amount of potted plants for our wellbeing, with their analysis surprising them by revealing that to discover “too much” decorative nature can actually hinder mental health, rather than help. The team from California's Stanford University developed a new method to quantify varying “doses” of greenery and wooden materials—and used this, in a simulated office, to probe the effect of indoor nature on people’s wellbeing. While a handful of potted plants and a window with a view of trees enhanced participants’ perceived restoration and sense of belonging, they became stressed when the greenery in the office grew more crowded, according to the researchers. "I wasn't expecting this at all," study author and civil engineer Eva Bianchi said in a statement. "Around 60 percent total greenery and wood had the highest stress increase, which was contradictory to prior work." While previous research had suggested that indoor nature like plants reduces stress—a conclusion not necessarily wrong—such studies either tested participant's response to nature versus without it, or were based on subjective levels of greenery. "There's such a huge body of literature, but we can't actually synthesize it, because no one's using the same methods," explained paper author professor Sarah Billington in a statement. To help test responses to different doses of indoor nature, the team developed a software called the Nature View Potential tool that calculates how much nature you see, on average, inside a given space. Using this, alongside 3D modelling software, they designed 11 digital conference rooms with varying levels of wood, greenery and nature views visible out of windows. The researchers recruited 412 participants, each of whom was assigned one of the virtual rooms and told to imagine that it was their new workplace, within which they were going to undertake professional development tasks. The team then set about stressing out the participants, as to to determine if the natural features in the rooms helped to ease this stress or not. Having already filled out questionnaires to gauge measures of their wellbeing, the participants completed tasks that included difficult anagrams and counting down from 1,022 to zero in increments of 13. "I told them they had scored below average and that they weren't going to get paid," said Bianchi, intending to add more pressure, before they filled out the questionnaire again. (All participants were paid in the end!) The researcher’s analysis revealed that a greenery dose of about 20 percent had the strongest result in terms of restorating calm and a sense of belonging for participants. "Any nature helps, but if you really want to see an improvement, you have to get up to around that value," said Billington. In contrast, the virtual rooms with the most nature—at 60 percent full of plants, living walls and wooden ceilings—the participants experienced elevated stress. Too much nature may lead to people feeling overwhelmed in indoor spaces, the researchers suggest. Some of the participants even wrote “too many plants" and "probably a nightmare to try to get anything done.” Meanwhile, wooden furniture and features alone appeared to have no effect on wellbeing measures. (The team note, however, that this may have been because the digital wood in their study was not realistic enough—as previous studies had found an effect.) As well as the dose-dependent relationship, the researchers report that it seems a feeling of “connection” to nature was the key to experience wellbeing benefits from indoor greenery. “You don't just put a bunch of nature inside the space," said Bianchi. "You make sure that the nature that you're putting inside the space will successfully make the occupants feel connected to nature." The authors acknowledge that how much nature we need will ultimately depend on the type of space under consideration and the wellbeing elements needed in that particular environment. “However, with the results of the present study, it appears that a dose of 20 percent of greenery may maximize belonging, fascination, being away and scope while limiting the reduction in coherence and positive arousal,” they wrote in the paper. Beyond providing guidance for the occupant, they hope their findings can inform design recommendations for housing, schools, workplaces and hospitals. “In an increasingly urbanized world, further research, particularly field work, on indoor dose of nature and wellbeing will become essential.” Newsweek has reached out to the researchers for additional comment. Do you have a tip on a health story that Newsweek should be covering? Do you have a question about plants and wellbeing? Let us know via health@newsweek.com. Reference
