Bringing plants into our homes is not a modern concept. Already the Egyptians and Romans decorated their houses with plants more than 2000 years ago. Plants in an otherwise plain room make you happy. Taking care of your little green friends makes you feel relaxed and at ease. Plants in hospital rooms lighten the mood and make you feel a little bit more at home and plants on your office desk increase your productivity. Is there actual science behind these believes and feelings? Let’s find out.
Plants affect our well-being
Being in nature has a huge positive impact on our mental state. But not just being outdoors, already looking outside of a window, viewing green landscapes increases our well-being. It positively affects mental alertness and productivity and at the same time reduces stress and anxiety. Many studies investigated the effect of indoor plants on our psychological and physical well-being. Research has been conducted i.a. in schools, hospitals, homes, universities and offices. Here are two examples:
To explore the impact of indoor plants on office workers, 51 participants were divided into 2 groups: One group worked in offices with no plants, the other group was placed in identical offices but with 13 small plants placed on the window still and one large plant placed on the floor with 4 smaller ones in front of it. Over the next 3 months, researchers followed up health and discomfort symptoms. Study participants, who were exposed to plants, showed a 21 % lower total symptom score, which means they were less fatigue, showed less dry throat and cough as well as less dry facial skin.
More recent studies involve more participants to answer the question if indoor plants increase happiness like an Iranian study with 384 female high school students that lasted for 3 months. Comparing the degree of happiness of students in classrooms with and without plants showed that the happiness score was significantly higher when students were exposed to plants. For this experiment 4 Epipremnum aureum plants (see the image) were placed into each corner of the classroom on a small table, so that they were visible to everyone in the class. It is astonishing that already 4 plants can impact our happiness level to such a great extent.
In a nutshell: many psychological benefits have been linked with indoor plants like positive changes in cognition, emotion, and physiology. Experiments in hospitals also showed that the list further includes reduction of symptoms of poor health, shorter hospital stays, and fewer headaches as well as increased pain tolerance and reduced stress.
Some studies investigated if the positive effect of viewing nature lasts if people are exposed to artificial windows in an otherwise windowless environment. Interestingly, also artificial windows can enhance mood and the perception of reality. Still, it appears as if indoor plants have a stronger effect on psychological well-being.
However, I have to tell you that due to strong variability in experimental methods and results, some experts are still in doubt if there really is a positive effect of indoor plants on our well-being. But even if it’s still in question, why would we respond to plants at all? What is the biological and psychological reason for humans to be influenced by the presence or absence of plants?
Why do we respond?
Experts see the main reason why we respond to plants in the history of humankind. It’s assumed that we all have an innate (inborn) preference and a learned (acquired) preference for specific plants and landscapes. This is supported by an experiment of Balling and Falk from 1982. In this experiment adults and children were asked to choose their preferred landscape out of several pictures portraying different biomes. While adults preferred images of the African savanna as well as pictures of the biome where they grew up, children clearly favored pictures of the savanna. Experts think that this preference is due to our survival instincts.
2 million years ago, when humans were still roaming the African savanna, it was crucial to the survival of the group to understand environmental cues to find the best place for shelter and food. Some of this knowledge is still in us.
For example, we respond more positively towards trees with a widespread canopy and shorter trunks compared to conical, globose, or columnar trees. Specific shapes guarantee better habitats for human survival. We also respond to tree color: green and red trees are preferred over purple and orange-brown trees. Also, this is assumed to be an innate survival instinct. Trees that have become yellow-brown in color might be nutrient deficient. In fact, Macaques monkeys show a similar response. Their color vision is identical to that of humans. Macaques monkeys prefer leaves with a specific color as food. These leaves have been shown to correspond to a higher nutrient level.
Next to tree shape and color, also other environmental cues like species diversity and appearance of geometrical forms seem to influence our preference for landscapes. Species diversity might provide a higher chance for eatable plants than monocultures. Interestingly, the feeling of well-being increases in parks with greater plant and bird diversity, but is independent of butterfly diversity.
We also respond more positively to the appearance of fractals in landscapes. Fractals are repetitive forms and patterns that are self-similar with increasing scale. Romanesco is an example of a vegetable with fractal patterns. We can also find this in the branching patterns of trees. Especially fractal patterns with a ratio of 1.3 to 1.5 appear pleasing to our eyes. Interestingly, people also experience lower stress when looking at fractal patterns, even if artificially created (like the tree in the image below).
To sum this article up: next time when you are stressed, take a break close to a window and just look at the landscape for a few minutes. And if that’s not possible, decorate your office or home with more plants, take a walk in nature more frequently or at least hang up pictures of plants, as these all have been shown to positively affect our physical and mental well-being. And next time, when you’re standing in a shop, thinking if you really need another plant for your home, just go ahead and buy it. It will make you happy!
Sources:
Bringslimark, T., Hartig, T., & Patil, G. G. (2009). The psychological benefits of indoor plants: A critical review of the experimental literature. Journal of Environmental Psychology, 29(4), 422-433.
Najafi, N., & Keshmiri, H. (2019). The relationship between classroom indoor plants and happiness of female high school students. International Journal of School Health, 6(1), 1-4.
Kim, J., Cha, S. H., Koo, C., & Tang, S. K. (2018). The effects of indoor plants and artificial windows in an underground environment. Building and Environment, 138, 53-62.
Kaufman, A. J., & Lohr, V. I. (2002, August). Does plant color affect emotional and physiological responses to landscapes?. In XXVI International Horticultural Congress: Expanding Roles for Horticulture in Improving Human Well-Being and Life Quality 639 (pp. 229-233).
Park, S. H., & Mattson, R. H. (2009). Ornamental indoor plants in hospital rooms enhanced health outcomes of patients recovering from surgery. The journal of alternative and complementary medicine, 15(9), 975-980.
Lohr, V. I. (2009, June). What are the benefits of plants indoors and why do we respond positively to them?. In II International Conference on Landscape and Urban Horticulture 881 (pp. 675-682).
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