“Various properties of plants, such as appearance, smell and feel, impact us in so many ways,” said Mengmeng Gu, associate professor of horticultural sciences at Texas A&M University. “They can feel good to the touch, make a space more fragrant and please our eyes.”
But how and why do plants have such positive effects on us? Here’s a look at research from the past few decades that has shown how houseplants affect our psychological and physical health.
People and plants are naturally connected. Humans have an intrinsic connection to plants and other living things, according to what is known as the biophilia hypothesis, an idea popularized in 1984 by naturalist and writer EO Wilson. Since then, more than three decades of research around the world have confirmed the hypothesis and demonstrated that natural environments have a considerable effect on increasing positive emotions and decreasing negative ones.
“When people affirm the common belief that being in nature relaxes them, that it helps them recover from stress and tragedy, that it is a healing process to be in nature, we now know there is a solid foundation for that,” he said. Wilson said in a 2015 interview with the Washington Post.
And as people started spending more time indoors, we brought pieces of the natural world to continue feeling connected.
Plants can quickly improve mood. Our connection with plants is so strong that sometimes it only takes a few minutes of being in their presence to start feeling better. Studies have found that less than 20 minutes is enough to make us feel more at peace. In one experiment, participants who spent as much as 5 to 10 minutes in a room with few houseplants felt happier and more satisfied than those in a room without plants. In another study, participants felt calmer and more positive after spending 15 minutes in a room near a tall plant (about five feet) than other objects.
However, Gu reminds us that “it’s not just seeing a plant that improves our mood so quickly, but smells can make a huge difference too,” although studies on the effects of plants on the non-visual senses are limited.
Plants bring relief to enclosed spaces. If you are stuck in an office or other small space for hours, plants can cause feelings of escape. In a study conducted during pandemic home stay orders, participants who had houseplants experienced significantly fewer symptoms of depression and anxiety than those who did not. Being surrounded by houseplants has led to feelings of “being away” from social or physical demands.
Plants can reduce stress. Other studies have shown that interaction with plants suppresses the system in our body that is activated when we perceive warning signs. Young adults in one study who spent a few minutes repotting and transplanting a houseplant reported feeling far less stressed at the end of the task than their peers engaged in a computer activity. Additionally, blood pressure measurements were much lower among people who handled the plants, suggesting that plants have the potential to dull the body’s fight-or-flight response.
Plants can recharge us. “Plants also have tremendous restorative capacity,” said Melinda Knuth, assistant professor of horticultural sciences at North Carolina State University. “Whether it’s outdoors like in a courtyard or indoors with houseplants, nature can help us feel recharged and down to earth.”
When we focus on demanding activities for a long time, such as our job, it can lead to mental fatigue and negative emotions that can affect the ability to pay attention. Seeing a plant in this situation can provide a spark of interest, redirect our attention, and restore our exhausted mental and physical resources – an idea known as attention restoration theory. Studies have found that the “restorative” effect induced by plants has a broad scope: renewing positive emotions and increasing productivity, creativity and attention span.
A data-driven guide to investing in houseplants
How do you choose houseplants to buy? The research can provide some practical indications:
Number of plants: While there is no magic number, having five or more foliage plants can increase positive emotions. For example, in one study, participants in a room with bamboo palm trees, Chinese evergreens, and heart-leafed philodendrons (five in total) felt more carefree and friendlier than those in rooms without plants. Alternatively, a tall (about five feet) potted plant or three or more small flowers (such as sweet peas, larkspurs, or wood sage) can elicit similarly positive responses.
Color: The greener, the better? In a study using English ivy, the yellow-green and bright green leaves increased feelings of cheer and relaxation, while the whitish-green leaves stimulated mostly negative emotions. As for flowering plants, one study found that purple, green, red, pink, and white plants could lower people’s blood pressure and heart rate. However, the purple and green flowers were more effective in relaxing the body, reducing anxiety, and improving mood. Another study found that red and yellow roses elicited a more calming response than white ones.
Real vs artificial: In an indoor space, having any kind of greenery, including plant photographs, is better than having none at all. However, real plants have a greater effect on mood, attention and relaxation than fake plants. The same goes for real and fake flowers. In a study of high school students, participants who looked at pansies for three minutes felt more relaxed and comfortable than those who looked at artificial ones. Gu’s point on the effects of mood beyond visual cues can help explain these findings.
Positioning: Although research on this is sparse, some studies suggest that having plants closer than 10 feet to a person has a positive effect on mood. A Knuth study of the state of North Carolina shows that most people put houseplants in living rooms, bedrooms, and sometimes kitchens. As home work expands, it can be beneficial to place plants in home offices or other work areas.
It is important to remember the caveats of many of these studies: some were conducted in highly controlled settings and mainly among college students. They reflect snapshots of time rather than long-term effects. And their real-world implications for a more diverse group of people, such as the elderly or those in resource-constrained environments, may be different. But it’s hard to ignore the volume of research showing that houseplants have a significantly positive effect on mood and physical health. So, as we find ourselves spending more time indoors, either due to the pandemic, work or weather, maybe it’s time to harvest some houseplants.
Lala Tanmoy Das is an MD-PhD student in New York City who does research in molecular cardiology. Find it on Twitter: @TanmoyDasLala.