The Influence of Greenery on Learning

“Compared to most of the interventions aimed at relieving stress (e.g. emotional skill building, anger management, positive behavior programs), placing trees and shrubs on the school ground is a modest, low-cost intervention that is likely to have long-lasting effects on generations of students.”

—Li & Sullivan, 2016

When Joe walks around his neighborhood, he is surrounded by sepia-toned brick buildings. When he goes to bed at night, he sleeps, fitfully, to the vehicular chorus of the Grand Concourse, a symphony of sirens, revving motors, car alarms, and bass blasting from souped up subwoofers. His access to nature is primarily derived from TV shows and a small city park a few blocks away, scattered with trash-strewn weeds. Joe (not any of my former students’ real name) is a 5th grader living in a dense urban area of the Bronx.

Joe’s neighborhood from a bird’s eye view, courtesy of Google Maps

You might be forgiven for assuming this is all so normal for Joe that he has neither any conception nor desire for the vistas his peers raised in lusher landscapes have constant access to. Yet when Joe came to interview at the middle school where I worked (we interviewed our prospective 6th graders) and was asked, “What would you like to improve in your community?”, he replied that he would like to reduce trash and noise, and, furthermore, that he would like to live somewhere with more space and trees.

It wasn’t only Joe who responded in this way. Other students we interviewed voiced similar wishes, though they said it in different ways. For one it was a desire for more flowers, for another less violence, or a bigger bedroom, or a backyard, or no upstairs neighbor who made so much noise. I haven’t surveyed all the kids in the poorest areas of the city, but I’d wager they’d also appreciate a little more peace and quiet or nature, if given half the chance to express it.

Actually, many kids have been asked, and their answers were uncannily similar to Joe’s. In the early 1970s, urban designer Kevin Lynch organized a survey of teenagers in cities across four different countries. “When children were asked to imagine the best place to live in, they often mentioned trees, and as beautiful places, gardens, and parks” (Lynch, 1977, as summarized by Chawla, 2015, p. 436).

A craving for access to a beautiful natural expanse may be an intrinsic aspect of being human. There’s even a term for this, biophilia (introduced by Erich Fromm in 1973 and expanded on by E.O. Wilson in a 1986 book by the same name), which means that we have an innate urge to connect to nature and other living things. This doesn’t mean everyone wants to go camping nor be anywhere near a wilderness. But at the very least, we are all likely sustained by an occasional walk through a stand of whispering trees or an urban garden, just as we are by a visit with a friend.

In fact, even a mere view of living green things out of a window can be vicariously invigorating, as a wide array of studies have shown in a wide variety of settings, from our homes and neighborhoods to institutional settings such as hospitals, prisons, offices and—of course—our schools.

The Impact of A Green View on Student Learning

A Room With a View

The idea that greenery could be rejuvenating was kickstarted by an influential study in 1984 by Roger Ulrich, in which he found that surgical patients in a hospital whose windows looked out onto trees recovered more quickly—and with less pain medication—than patients in rooms facing a drab brick wall.

Prison inmates similarly benefit from glimpses of nature. A study found that prisoners in cells with outward facing views of farmland were sick less often than their counterparts with views of the inner yard (Moore, 1981). Of prison inmates, there are none more deprived than those placed in solitary confinement: they are enclosed in a cell for up to 23 hours a day for days, months—sometimes years—on end. Forget windows. Just showing videos of natural landscapes to prisoners in solitary confinement can help them to remain calm and reduce violent behavior (Nalini, et al., 2017).

Perhaps it is unsurprising people confined, whether to a hospital bed or a prison cell, would benefit from a small peek at something, anything, vibrant and alive. What may be more surprising is how subsequent studies have shown that “views of nature out of an office or factory are associated with increased employee productivity, enhanced feelings of job and life satisfaction, greater psychological and physical well-being, and reduced levels of frustration and stress” (Matsuoka, 2010, p. 274). This suggests that a green vista is not only a spark of life to a desperate inmate or sick patient, but a rejuvenative force for all of us who toil indoors for the majority of our day.

An accumulating stream of studies have shown that views and access to green space can improve the well-being and learning of students in K-12 schools. Greenery around a school building supports an increase in test scores, grades, working memory, attention, and plans to attend a four year college, with a concomitant decrease in stress and criminal behavior (Matsuoka, 2010; Wu et al., 2014; Dadvend et al., 2015; Li & Sullivan, 2016; Hodsen & Sanders, 2017; Kweon et al., 2017). Furthermore, greenery in a student's neighborhood can result in an increase in mental health and a decrease in aggression (Alcock et al., 2014; Younan et al., 2016).

Sounds too good to be true? Maybe you think this is fluffy sociological stuff written to assuage the confirmation bias of tree huggers. It certainly sounds fluffy to say greenery is calming. We could say the same sort of thing about aromatherapy, crystals, and listening to whale sounds. But the significant and positive impact of the presence of greenery has been confirmed through randomized controlled trials and longitudinal studies. Fluffy? Maybe not so much.

There’s two theories about why greenery is rejuvenative: one is Attention Restoration Theory (ART) and the other is Stress Reduction Theory (SRT). ART theorizes that green space restores focus and fights fatigue, whereas SRT hypothesizes that nature reduces stress. Both theories have evidence to back them up, so there may be some interplay between reducing stress and restoring focus.

The natural views that seem to wield the greatest restorative and calming effects are from a school’s cafeteria and hallways (Matsuoka, 2010; Li & Sullivan, 2016). Li and Sullivan’s study suggests that “a 10-min break [with a natural view] would suffice in restoring students’ attentional capacities and help them recover from stressful tasks” (p. 156). Another study found even only five minutes of exposure to nature could help to reduce stress (Barton & Pretty, 2010; as cited by Kweon et al., 2017, p. 36). Ensuring that cafeterias, hallways, and other spaces, such as gyms, have a sightline to nature could be an effective way to support students in reducing their stress and restoring their ability to focus when they return to class.

According to one randomized controlled experiment, views of green expanses from a classroom can also support the cognitive performance of students, leading to 13% greater attentiveness than students with views of a parking lot, other buildings, or without any windows (Li & Sullivan, 2016). Another study found that schools with higher levels of nearby tree canopy cover had higher scores on tests of reading comprehension (Hodsen & Sander, 2017). One study even suggests that a mere glance of 40 seconds out of a window onto a green roof rather than a concrete one can serve to sustain attention on a challenging task (Lee et al., 2015).

And we’re still just talking about the presence of greenery outside of a school building. What kind of greenery is most influential? What about greenery within a building? And what about getting kids out of a building to interact with the real thing?

It’s All In the Canopy

Greenery, or green space, could mean a wide variety of things. Are we talking grass? Shrubs? Trees? Astroturf? Let me give you a hint. It’s not lawns. It’s not athletic fields. In fact, those land features, along with parking lots, are associated with reduced academic goals and achievement, and even higher criminal activity (Kweon et al., 2017). Shrubs don’t really do much, either.

It’s those trees, man. It’s that breathing green canopy cover that is the most focusing, calming, and restorative.

This isn’t so strange, when you think about it. Dallying under the dappled shade of trees is the hallmark of the good life. That soothing sound of breeze moving through leaves. The way sunlight shimmers across a variegated green marquee. There’s just something about trees. Something magical and magisterial. They buffer us from wind and rain. They enrich and entrench the soil and bear us fruit. They even communicate to one another through their root systems (Wohlleben, 2015). Some live on a timespan so protracted it’s unfathomable to our puny human minds. Trees bestow us with a sense, however subconscious, of flourishing ethereality that we may only most appreciate in their absence.

I was fortunate to grow up with this stout olive tree poised outside my bedroom.

More practically, trees also help to reduce air and noise pollution, and help get people to exercise more (Dadvand et al., 2015). Trees can do much to not only “soak up fine particle pollution from cars, power plants, and factories” but furthermore “cool down neighborhoods anywhere from 0.5 degrees Celsius to 2 degrees Celsius on the hottest summer days” (Plumer, 2016). Pleasing on the eyes? Check. Providing ecosystem services for the public health and well-being of mankind? Check.

It is possible that trees only have a restorative visual impact within a certain range of density. For example, one study suggests somewhere between 24-34% tree cover* is a sweet spot (Jiang et al., 2014). Intriguingly, this may reflect an evolutionary preference for savannah-like landscapes and acacia-like—or thin trunk, large canopy—tree forms (Falk & Balling, 2010). Another study suggests that it’s not simply about the quantity of trees, but the quality of those trees, such as how well maintained, varied, and orderly they are (De Vries, van Dillen, Groenewegen, & Spreeuwenberg, 2013). This makes more sense. You could meet any quantitative quota with a sickly or monotonous row of trees, but a healthy, diverse copse will do much more for both your health and your soul.

I suspect there’s something about the just-right visual complexity and dimensionality of a healthy tree canopy that is especially pleasing to our mind’s eye—there’s just enough subtle unpredictable movement, variation, and depth to stimulate, while just enough light and green shade to soothe. In fact, there is the possibility that it is the fractal nature of tree canopy that makes it so pleasing to the eye and the brain (Cepelewicz, 2017).

In barren environments, like the flat expanses of the interstate highway in Kansas or like most school playgrounds, our minds grow desperate for distraction. And indeed, one study found that if a school has a barren playground, children with ADHD have greater difficulty concentrating after recess (Taylor & Kuo, 2001).

Man-made visual complexity, such as urban landscapes, can certainly inspire their own form of awe and appreciation, but as of yet, our architecture can hardly replicate—in a cost effective manner—the gentle scintillations of leaves nor the myriad other environmental benefits, like air filtration, that trees provide.

I’m going to go out on a limb here. I think we need trees not only to feel most fully alive, but in order to truly live.

*Having trouble visualizing what 24-34% tree cover looks like? I was, too. Fortunately, MIT offers a nifty tool that provides percentages for the density of tree cover in cities across the world. Head to senseable.mit.edu/treepedia to take a peek. You can zoom in on a specific spot in a city that has a density within that range, then pull up Google Streetview to get a ground-level visual. Compare between spots with a large percentage of tree cover, such as 50%, to ones with barely any, such as 2%. That disparity will give you an idea why there may be a sweet spot for restorative effects, at least from a visual standpoint.

Trees and Green Spaces Combat Inequality

Here’s a riddle for you: how can you tell the difference between a poor and affluent urban neighborhood from outer space?

A more expensive neighborhood only 4 miles away from Joe, also courtesy of Google Maps

Yep. It’s that mass of green.

One longitudinal study found just moving to a greener urban area not only immediately improves mental health, but sustains positive psychological benefits for at least three years (Alcock et al., 2014). That’s all well and good, but there’s another compelling reason to get more trees into your ‘hood: they help raise the property value (Mullaney, Lucke, & Trueman, 2015). Even better yet, “planting 10 or more trees per city block is equivalent to increasing the income of every household in that city block by more than $10,000” by improving perceptions of health, while decreasing “cardio-metabolic” conditions such as diabetes, hypertension, obesity, high cholesterol, and heart disease (Kardan et al., 2015).

Not many can afford to move to a greener area, but even small injections of green into dense urban neighborhoods, like replacing vacant lots with gardens, can reduce symptoms of depression in local residents (South et al., 2018). A longitudinal study in 2016 by Diana Younan and her colleagues furthermore found that green space in urban neighborhoods in Southern California reduced aggressive behavior in teens. The researchers found no evidence that this effect was strongly influenced by either sociodemographics nor the quality of the neighborhood, which suggests “the universal benefits of neighborhood greenspace” (p. 9). This corresponds with research showing that “building areas with high levels of vegetation can have approximately 50% lower crime levels than areas with low levels of vegetation (Kuo & Sullivan, 2001), and a 10% increase in the amount of tree cover has been associated with a 12% decrease in crime (Troy, Grove, & O’Neil-Dunne, 2012)” (as cited by Mullaney, Lucke, and Trueman, 2015, p. 159).

Joe and many other children in our densest urban areas crave natural environments with green space and restorative shade. One of the most sustainable and cost-effective interventions we can take to support future generations of children is simply to plant more trees—most especially near homes and schools.

Bringing Greenery Into Schools

    Here’s the reality, though. Most schools are already built, and whether or not they are so lucky as to have any windows, let alone views of trees, is entirely outside the realm of their direct and immediate control. We may not be able to plant trees in classrooms, but is there any way we could bring some of that green juju indoors?

This is a school, not a prison.

Some research suggests that the presence of plants in a hospital room can increase tolerance for pain (Grinde & Patil, 2009), while indoor plants in an office may reduce fatigue and health complaints (Grinde & Patil, 2009; Ranaas et al., 2011). But most of the research on the impact of indoor plants on classroom well-being, performance, or stress reduction, while suggestive, remains mostly inconclusive (Doxey, Waliczek, & Zajicek, 2009; Han, 2009, 2018; Berg et al., 2016). 

I’ve been grappling with this, given the more robust effects for outdoor greenery. Is it because potted plants in most studies are not selected and situated primarily for visual complexity? If there were more plants or greenwalls with a diversity of size, form, and color placed around a classroom, could these have greater restorative effects?

There may be a sweet spot between quantity and quality which has not yet been discovered for indoor plants. Each study uses different variations and configurations of plants. As one reviewer put it, “although the evidence suggests indoor plants can provide psychological benefits, the heterogeneity amongst the methods and results may imply the benefits are contingent on the context of the encounter with indoor plants and the participants in the experiment” (Burnard & Kutnar, 2015, p. 972).

Furthermore, no study (to my knowledge) has yet examined the two areas where green views are most likely to have the greatest restorative impact: school cafeterias and hallways. Clearly, we need further research (while we’re waiting on the research, to add some dimensionality to your own indoor plant collection, try placing plants at different heights, such as on stools, boxes, or crates, as “garden stylist” Satoshi Kawamoto suggests (Gordon, 2015)). But here’s a short quiz that may help you to determine whether or not you want to bring plants into your classroom or school: 

Let your answer to this be your guide.

Indoor Plants for Air Filtration?

Even if they may not have the fully restorative or stress reducing impacts that views of outside tree canopy can provide, could they filter and reduce indoor air pollution? If they could, this would be huge because poor indoor air quality impacts learning. Effects reported by various studies have been a reduction in cognitive performance and the ability to make complex decisions, and an increase in sleepiness (Carrer, 2018). In other words, everything you don’t want in a classroom.

This tiny drab classroom could sure use some green air filtration.

A widely cited NASA study in 1989 (Wolverton, Johnson, & Bounds) found that a wide variety of plants filtered volatile organic compounds (VOCs) often present in indoor environments, such as formaldehyde, benzene, and ammonia. Some later studies support this initial finding (Pettit, Irga, & Torpy, 2018), but unfortunately, it seems that outside of a lab setting and in the much larger, real-world spaces of offices and schools, plants do very little to filter indoor air (Meyer, 2019). Well, OK, maybe they don’t filter pollution much, but another side benefit of indoor plants is that through the process of transpiration, they can add moisture to the air, which is good for dry skin (Horton, 2015).

Overall, unfortunately, it appears that indoor plants do not provide the same benefits that outside greenery does.

Keeping plants in a school requires careful consideration, such as how much daylight, if any, is available in a given space, as well as who will be responsible for watering and upkeep, not to mention the issue of safety. Ideally, the plants you select should require little sunlight and watering, provide air filtration benefits, be visually appealing, and highly durable.

Through a survey of friends and online sources, I drew up a shortlist of promising plants for school use, most of which are within the $15-30 range if you buy them pre-potted:

If you are fortunate enough to have access to some sunlight in your school or classroom, then look also into the following:

If you are even more fortunate and can secure funds, you could also consider the installation of greenwalls. While further research is required, there is potential in the biofiltration potential of a greenwall (Pettit, Irga, & Torpy, 2018), as well as possible restorative effects (Berg et al., 2017).

Bringing Schools Into Greenery

So far we’ve focused primarily on the mere presence of trees and greenery, which even passively can be powerful for learning and health by reducing stress and increasing attention, in addition to reducing pollution. But given our focus on education, the logical next question is: does interacting with nature amplify and deepen these effects?

The answer thus far, at least according to research on playgrounds and gardens, is “Yes.” School gardens help to increase physical activity (Wells, Myers, & Henderson, 2014), while playgrounds that are surrounded by greenery promote better cognitive functioning (Kuo, 2010), “concentration and relief from stress,” in addition to more imaginative, explorative, and socially cooperative play (Chalwa, 2015, p. 445). It should also be recognized that just spending time in nature can support the development of stronger immune systems. One study found that walking in a forest boosted anti-cancer cells by 50% or more, which remained elevated even a month after returning to everyday urban existence, while also decreasing inflammation (Li, 2010, Mao et al., 2012, as cited by Kuo, 2015, p. 4).

But there is much more to interacting with nature than the solely utilitarian benefits to health and well-being. Access to nature provides opportunities to build greater self and world knowledge. How can you truly understand how food grows, or how plants utilize photosynthesis, or what it means to cultivate microbial soil life, unless you get your hands dirty? How can you truly develop resilience, fortitude, and patience without having experienced the alternating awe and weariness of spending a day walking through the woods or up a mountain? Some studies have suggested that simply playing in nature increases the likelihood of environmental stewardship later in life (Wells & Lekies, 2006; Thompson et al. 2008). Imagine having a curriculum that includes not only reading, writing, and ‘rithmetic, but moreover a scientific and aesthetic engagement with real plots of land?

Hosting school outside may sound radical at first, but ‘forest kindergartens’ are a thing in Germany, Finland, Switzerland, and . . . Vermont (Gregory, 2017; Schoolsoutfilm.com, 2012; Walker, 2016; Hanford, 2015). Given the research we’ve just reviewed, such seemingly hippie-dippy programs now seem eminently sensible. The key hurdle is whether you happen to have a forest handy nearby. But what about schools in local parks? Actually, I wrote that sentence, then poked around on the web for a minute, and lo and behold, there’s classes called Tinkergarten at a park near me that promotes learning through play in local outdoor spaces (and maybe one near you; check it out at tinkergarten.com).

Humanity now faces repercussions from the incredible stress we have placed on the natural world. The great diversity of microbes, habitats, plants, and animals our earth once carried is swiftly ebbing. Traditional ways of living and knowing are preserved primarily for entertainment, rather than as respected sources of wisdom. If developing an appreciation of nature, both scientific and aesthetic, means getting children outside into whatever local park, water feature, grassy knoll, garden, flower box, or forest you may be fortunate enough to have near to your home or school, then let’s do it. If it means bringing plants into a school via hydroponics, as teacher Stephen Ritz does at CS 55 in the Bronx (Check out Ritz’ website greenbronxmachine.org or read his book, The Power of a Plant, to learn more about his work), or via potted plants or greenwalls, or lining playgrounds, starting rooftop gardens, or even just gazing out at a natural landscape from windows or in videos . . . then, hey. We’ve got to start somewhere.

What We Can Do

Trees take a long time to grow. Unfortunately, leaders in education tend to focus on shallower, shorter-term initiatives, like tablets or teacher evaluations.

There has been a growing recognition of the general importance of greenery in our communities, and many trees have been planted in areas that were once urban deserts. Here in NYC, organizations like GrowNYC, Bronx Green-Up, Learning Gardens, and many others are available to help get kids get their hands dirty in a garden. And city-wide initiatives like Greenstreets and MillionTreesNYC have brought street trees to nearly every block. 

For students like Joe living in dense urban neighborhoods, this means a lot. But having a row of street trees is not enough. We need more vacant lots converted to green space, more green roofs, more parks, and far, far greater access and opportunities to interact with nature on a frequent basis.

It may be that growing a green thumb may be one of the most beneficial things you could do to support the learning of future generations.

In Sum

Extra Credit: The Ecology of Greenery

Clearly, it’s not within any individual school’s purview alone to increase the greenery within a neighborhood, and nor is one dedicated community organization that receives some grant funding enough. It takes a coordinated effort between local businesses, governmental agencies at different levels, nonprofits, and civically engaged citizens to make it happen. It truly takes a community to plant, sustain, and scale the kind of quality tree canopy our children need.

Caring for plants—and for animals—can not only strengthen a community, but also provide therapeutic benefits for individuals.

Bill Thomas, a NY professor and physician on a mission to improve the care of our elderly, has come up with a model of elderly care he calls the “Eden Alternative” (Bahrampour, 2016). Instead of cold, clinical institutions, he creates environments that are more akin to gardens. He stocks nursing homes with cats, dogs, rabbits, and birds in addition to an array of plants. The effect is reduced need for medication, lower death rates, raised spirits, and greater autonomy.

In Baltimore, one volunteer, Gene DeSantis, has planted over 15,000 trees, overcoming a childhood of trauma while contributing to the long-term health and well-being of his community (Zaleski, 2019).

In D.C., a former drug dealer's love of birds helps him to discover his better self. He now works with children, introducing them to the beauty of raptors, to help them learn to engage with the natural world, and in the process, also discover their better selves (Daniel, 2016).

In schools across our nation, our children are struggling to cope with chronic and acute stress, trauma, and poverty while attempting to learn in environments that offer little rejuvenation nor tranquility.

It’s not only the immediate adults around them who need to build lattices and networks of love, resilience, and calm, but furthermore the sustaining canopies and anchored roots of trees in the land that surrounds them, planted and nurtured by the many diverse people, groups, and organizations of their community.

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