Studies have shown that plants in homes and workplaces help reduce stress, increase productivity, enhance employee attitudes, lower operating costs, help in “green building” design, and improve air quality. Although many of these studies involved workplaces, the principles apply to homes as well.
A Human Spaces report in 2015 on biophilic design showed that, globally, nearly two-thirds of workers have no plants in their workspaces. Those spaces which incorporated plants and other natural elements reported 15 percent higher well-being and creativity, and six percent greater productivity. A 2014 study by the University of Exeter supports this, showing that just a few plants introduced into a work environment can increase the productivity of 15 percent.
Studies in Texas, Washington State, and England showed that employees in environments with plants were 12 percent more productive than those not exposed to interior plants. Visual exposure to plants helped to reduce blood pressure and recovery from stress within five minutes. A 2010 study by the University of Technology in Sydney quantified several reductions in workplace stress, just from plants. They found reductions of 37 percent in anxiety, 58 percent in depression, 44 percent in hostility, and 38 percent in fatigue. Since green is a calming color, this too should have some effect.
Perhaps some of the increased productivity with plants arises from the reduction in office noise, another factor well-documented in studies. For instance, a small indoor plant hedge around a workspace can reduce noise by five decibels. Plants absorb sound, rather than just insulate against it. A 1995 study from London South Bank University showed a positive effect on noise reduction from large plants placed along wall edges and in corners.
Surveys and studies have verified the positive effect of plants on employee perception and disposition. A key incentive for firms to have interior plant design and maintenance contracts is this, as well as employee retention. Plants have been shown to reduce employee absenteeism by 14 percent. It is cost effective to keep employees happy, this asset valued at ten times a building operating cost and 100 times the energy cost.
Plants cool by the process of “transpiration”, releasing moisture into the air. A USDA estimate is that proper use of plants could decrease air temperature in an office by as much as ten degrees. Plus, the moisture released by these plants helps maintain indoor humidity in the human comfort zone of 30 to 60 percent and helps prevent materials such as wood from cracking when dried out.
Similar to outdoor plants, indoor plants improve the perceived value of spaces, in addition to enhanced aesthetics. A study in England reinforces that indoor plants have a positive effect on perception while costing less than most other choices for corporate décor. Clients and employees perceive interior spaces with plants as more welcoming, relaxed, and upscale.
An often cited example of the positive effect of plants on perception and value is the study of the Opryland hotel in Nashville. Its occupancy rate is considerably higher than the national average. A scientific case study found that the main factor accounting for this high occupancy is the significant investment (over $1 million) in interior plants, in fact, one of the largest investments in indoor plants in the country. This hotel was planted with 12 acres of indoor space, containing about 18,000 indoor plants representing over 600 species.
A more recent investment in indoor plants, topping this one, was the opening in January 2018 of the glass-domed “spheres” at the Amazon headquarters in Seattle. These contain 40,000 indoor plants, representing over 400 species. This mirrors the trend with many other corporate firms adding plants, although on a smaller scale, to their interior environments. They are learning that the concept of “biophilia”—the innate human connection to nature—can make workplaces healthier and happier.
A pioneering study during the 1980’s was perhaps the first to show that interior plants can have a positive impact on “sick building syndrome.” This is the condition found in many tight, energy efficient buildings from indoor pollutants. These are the toxic chemicals from building components such as carpets, paints, and synthetic construction materials. Toxins include such compounds as xylene and benzene, with the most commonly found in EPA tests being formaldehyde at 0.173 micrograms per liter of air. Such tight buildings can be ten times more polluted than air outside or in “leaky” environments. An adequate installation of plants in sealed U.S. offices could save, by one estimate, $258 billion.
Rooms filled with plants were shown to have 50 to 60 percent fewer molds and bacteria in the air than in rooms where no plants were present. These, and toxins, both are absorbed in the soil, and into plant leaves. Toxins may be translocated down into the root and used there as plant food, or destroyed through a process called “metabolic breakdown”.
Plants grown in potting soil have been rated for their relative removal rate of toxins, such as formaldehyde. For this compound, Boston fern can remove 1863 micrograms per hour, bamboo palm 1350, Janet Craig dracaena 1328, English ivy 1120, peace lily 939, areca palm and corn plant 938 for examples. All the details of how plants clean such air, and how to use them for this, are in the classic paperback book “How to Grow Fresh Air” by the researcher B.C. Wolverton.
“Living walls” of plants have become more common in buildings, including modular units one can even install in a home. A company in Sydney (Australia) has partnered with the University of Technology there to quantify the positive effects of what they term “breathing walls” to remove carbon dioxide and volatile organic compounds from interior air. U.S. researchers Fisk and Rosenfeld of the Berkeley National Laboratory have quantified a $58 billion annual savings from sick-building illness with the use of plants.
In a small but important study by university professor Tove Fjeld in Oslo, Norway, plants were shown to improve employee health in offices, schools and hospitals. When plants were present, ailments such as fatigue, headache, sore throat, coughs, and dry skin were all reduced. The mean reduction of 12 ailments with plants present was 23 percent.
For office workers, just having a plant on the desk can improve the six to eight cubic feet of “personal breathing zone” where most the day is spent. Jay Naar, author of “Design for a Livable Planet”, suggests that only 15 to 20 plants can clean the air in a 1,500 square foot area. A good minimum would be two large (10- to 12-inch pots) plants per 100 square feet of space.
Whether you have a workplace, or just home, consider adding some indoor plants if you don’t have them already. Main considerations in choosing plants are their light, humidity and water needs. Most people prefer plants that are low maintenance with few, if any, pests and problems. Some good choices for bright, indirect light are spider plant, dracaena, and begonia. For lower light, consider peace lily, pothos, Chinese evergreen, or snake plant.
If you have pets, make sure to check the ASPCA website (www.aspca.org/pet-care), or with your vet, to make sure your plants are not toxic to them. If you have children, check with your doctor or local poison center (poisonhelp.hrsa.gov) on the safety of particular plants.
Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont