University of Vermont Extension
Department of Plant and Soil Science
PLANTS AT WORK, INDOORS
Dr. Leonard Perry, Extension Professor
University of Vermont
Plants at Work is a national information program of the green industry
to inform businesses and the public of the benefits of using plants
indoors. 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.
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 to lessen stress within five minutes. Perhaps some
of this arises from the reduction in office noise with the use of
plants, another factor well-documented in studies. For instance, a small
indoor plant hedge around a workspace can reduce noise by five decibels.
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 the employees
happy, this asset valued at 10 times the 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.
The main effect of plants on buildings environments, however, may be on
the outside. One young healthy tree, according to the International
Society of Arboriculture, has a net cooling effect equivalent to ten
room-size air conditioners operating 20 hours a day. Other industry
statistics indicate the proper use and placement of trees can lower
heating and cooling costs by up to 20 percent.
Similar to outdoor plants, indoor plants improve the perceived value of
spaces in addition to the 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
An often cited example of the positive effect of plants on perception
and value is the study of the Opryland hotel in Nashville. Its 85
percent occupancy is considerably higher than the 68 percent national
average. A scientific case study found 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 has 12 acres of indoor space, containing
about 18,000 indoor plants representing over 600 species.
A study over 20 years showed 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” as
shown in a study by German scientists.
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 paperback book by the researcher B.C.
In another fascinating study by a university professor Tove Fjeld in
Oslo, Norway, plants were shown to improve employee health in offices,
schools and hospitals. Plants were included or
not in offices during various periods for employees. 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, compared to without, was 23 percent.
U.S. researchers Fisk and Rosenfeld of the Berkeley National Laboratory
have quantified this into a $58 billion annual savings from
sick-building illness with the use of plants, 40 percent of all sick
days related to poor indoor air quality in their study. In addition,
they estimate an additional $200 billion could be saved using plants
indoors from improvements in worker performance.
You don’t have to think big to benefit from the use of plants indoors. A
Scottish brewer is an example of a firm that uses plants indoors
extensively, including planters on top of filing cabinets to divide
space, reduce noise, and to improve employee health and satisfaction.
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. Author Jay Naar suggests 15 to 20 plants can clean the air in a
1,500 square foot area.
You can learn more about the Plants At Work program, and the “green”
qualities of using plants indoors, at their website (www.plantsatwork.org)
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