We, as an industry, nearly always tote the benefits of
interior plants, and I’m here to tell you that it’s not just bullshit: there
are measurable effects in the way people think, behave and feel when they are
in an environment that contains plants versus one that does not, and plants
actually are able to clean the air we breathe.
Instead of doing what everyone else does, which is usually just
to concisely (we all know that’s my
strong suit, ha ha) list the same key points, I’ve done the legwork and
actually rustled up a few of the papers from which said points were drawn from,
and will point you to them so that you can read for yourself the results of
some of the various studies that have been conducted over time.
By all means be skeptical, and don’t take our word for it:
we’re very few of us scientists in this industry, but there has been real
scientific work done which really confirms what we’ve been saying all along:
that plants indoors have a direct effect on things like employee productivity,
reduction of airborne pollutants, and combating stress and fatigue.
Cleaning the Air
So for starters, do plants actually clean the air? It would
be a boring blog post indeed if I said no, so here are a few papers which
highlight some of the work that different plants (and their associated colonies
of soil-dwelling microorganisms) do to remove harmful chemicals from the
interior atmosphere. What I’m not going to do is tote the old NASA study that
gets thrown around so often: you can look that up for yourself, but Dr.
Wolverton (and others) have continued to do good research into this phenomenon
since the first study was published in the 80’s.
This study found that quite a few plant species, notably
Boston ferns, chrysanthemums, and dwarf date palms, were able to remove
appreciable amounts of these chemicals from the air inside sealed chambers.
Based on prior research into indoor air pollutants by the EPA, the
authors
calculated that an average-sized office constructed of typical building
materials would contain 3916 µg (micrograms) of formaldehyde (to use the most
sinister example in the paper). A single Boston ferns was shown to remove 1863 µg
of this formaldehyde- per hour! The mums and palms were not far behind, and
there was a decent list of other plants which were also quite effective at
removing formaldehyde from the air.
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| Figure 1 from the study linked above, showing formaldehyde concentrations being removed by a Boston fern. |
The other part of the study looked at the microorganisms
which colonize the rhizosphere (the area immediately surrounding plants’
roots), and the role they play in the removal of these chemicals. They found
that unsterilized soil was able to remove formaldehyde from the air while
sterilized soil was not, and that soil containing a plant was more effective
still. They found that different types of bacteria had an effect on how much
formaldehyde was removed, and the data indicated that different plants harbour
different types of soil bacteria. Check out the paper for yourself: I’ve linked
to it above.
This study performed similar experiments to the one above
(you can read it yourself for the full details), with a slightly different
method. Their results were similar: plants and their associated bacterial
communities removed airborne pollutants quite effectively from the atmosphere.
One point of note is that temperature and light had a large effect on the
experimental results, suggesting that plants are more effectively cleaning the
air when they are actively growing (see the portion in the discussion on uptake
of gases through stomata if you like), which really bolsters the case for
optimizing plant health in the interior landscaping in order to maximize this
beneficial effect.
Improving Employee
Productivity
This is a claim that is often used because it seems to infer
a real economic benefit to the client. I’m inclined to agree with the science,
and I can see that this certainly makes interior landscaping more marketable, but
it almost feels like a bribe: surely plants can be desirable of their own merit,
and surely the effect they have on people should not be measured in terms of
productivity but of general mental and physical health? Do clients actually
purchase plants to get more out of their staff? At any rate, the effect has
been measured in the following papers (and I’m sure there are more); let’s call
it here just an added bonus to the addition of plants to the workplace.
This is one of the commonly cited ones, in which the authors
noted a 12% increase in productivity (measured as reaction time to a computer
task). I’m not sure that this is really a rock-solid study, and I wish I could have
found another paper which replicated the experiment, but it’s here, for what
it’s worth. One more interesting point in the study is the result on the blood
pressure of the participants, which measured significantly lower during and
after completing a computer-based productivity task in participants in a room
with plants versus that of those in a room without.
I’m hoping that someone’s Japanese is better than mine and
they might comment on this paper, but based on the English abstract and the
figures in the results, these researchers found that viewing plants while performing
tasks on a visual display terminal (presumably a computer screen of some sort)
resulted in reduced visual fatigue when measured as critical flicker fusion
frequency (a somewhat complicated phenomenon that you can look up on your own).
I can’t comment much on this one, as I can’t even read it, but the numbers are
there.
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| Figure 2 from the productivity paper above, showing the number of correct associations by students who reported a high level of physical exhaustion. |
This is more of a press release than an actual paper, I
think, but it highlights the results of an experiment carried out by
researchers in The Netherlands, which found that, while no improvements to
productivity tasks were noted, there was a marked improvement in performance of
creative tasks. These improvements were even more dramatic with test subjects
with self-reported stress or exhaustion (the study used students as their
guinea pigs).
General Health and
Wellbeing
This is probably the most important one for me, because it
has much to do with the concept of biophilia, which I will be addressing soon
(likely at great length), and which is tied very closely to In Situ’s raison
d'être. We believe that humans have an innate subconscious need for
proximity to natural elements, and keeping plants indoors proves to be a
noteworthy way of satisfying this in our modern urban settings.
General mental health seems a difficult thing to quantify, but
the works below are able to convey a few measured benefits to having plants
around us while spending, as we typically do, the majority of our time indoors.
 |
| Figure 2 from the study above, showing changes in pulse transit time while watching first a gory video and then one of several others. |
This almost creepy lab study measured several parameters (heart
rate, muscle tension, etc.) during and after showing the poor participants videos
of people getting into violent industrial accidents, followed by a video of either
a fast-moving stream, a wooded area, or varying degrees of busy vehicle or foot
traffic. The results clearly showed that the wooded scene was very effective in
recovery from the stress indicated in the physical tests.
The self-report from the participants also indicates that
the nature scene was the most positively affective by far, and best able to
reduce anger, aggression and sadness.
This extensive study looked at various aspects of how keeping
plants indoors relates to human well-being, from mental and physical
standpoints. In section 5, the authors had their subjects complete Profile of
Mood States questionnaires (apparently a widely accepted method for measuring different psychological states) before and after the placement of varying numbers of
plants in their workspaces for a period of three months. The questionnaires covered such feelings as
tension/anxiety, fatigue, and confusion.
The data shows that plants did in fact affect these
parameters, and that the control group with no plants scored even worse on the
questionnaire than it initially had done, while the subjects with plants saw
their scores improve markedly.
This is also mostly a literature review, and includes quite
a few statistics from other authors’ papers (which is why I’ve included it
here), but the author points to two of her own studies, and I’d like to summarize
here the gist of the second one: in a survey rating employee satisfaction, the
availability of a view out of doors was considered far more valuable and
restorative if it contained natural elements, and became even more so the more
natural elements could be seen. Further to this, respondents with clear outside
views to natural elements reported feeling more positive about their work in
general. From the above:
“These results point
to the range of impacts that a view of nature can affect. Those with a view of
nature felt less frustrated and more patient, found their job more challenging,
expressed greater enthusiasm for it, and reported higher life satisfaction as
well as overall health.”
Pretty interesting stuff, I think. It will be interesting to
stay on top of the science and see what further studies come from this quarter.
If anyone has any further information on this they want to share (for or
against, of course, though I bet you’d be hard pressed to find a study against
plants in buildings), be sure to include it in the comments.
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