I love plants. I love looking at them. I love potting them. I love watering them. I love choosing sunny little spots for them to live in. The plant love is real. Among the countless frivolous reasons I have for loving plants, I also have some fairly legitimate reasons for thinking we should have more plants in more places, particularly in places where we are asking students to focus, stretch their minds, and explore new ideas. The research and science behind the benefits of houseplants in workspaces is very interesting and relatively sound.
1) Plants help us focus and make us more productive. Field research performed in 2014 by Nieuwenhuis et al. and reported in an article in the Journal of Experimental Psychology: Applied showed that workplace culture and productivity both improved notably in scenarios where the space in which employees worked featured houseplants. Exeter University's Dr. Knight has been studying this phenomenon for over a decade, finding that employee productivity increased by an average of 15% when bare workspaces were updated to include a few indoor plants. Employee performance also increased based on quantitative tests measuring memory retention and other skills following the inclusion of houseplants into the workspace.
2) Houseplants improve indoor air quality. Lacking the ventilation of outdoor spaces, indoor spaces can become fairly polluted. Air pollutants can emanate from adhesives, clothing, solvents, and a wide variety of other sources. Research by Stanley J. Kays from the University of Georgia showed that ornamental indoor plants are capable of filtering these pollutants from the air, improving physical and psychological wellbeing. More specifics on this research can be found here.
3) Plants help keep stress levels low. Chen-Yen Chang and Ping-Kun Chen published an article which investigated how window views and indoor plants impacted the levels of anxiety and nervousness of participants in the study. Stress levels were quantified by measuring participant's electromyography (EMG), electroencephalography (EEG), and blood volume pulse (BVP). Subjects were unilaterally found to display less stress and anxiety when watching a view of nature and/or when indoor plants were present as compared to the individuals who had neither of these things.
There is a pretty long list of additional suspected benefits or benefits in which the supporting research is a little shaky, but this list above is pretty soundly supported in my opinion. I firmly believe that including some greenery in the classroom has the potential to help some, if not all, students learn better. Particularly in New England, where a large portion of our year is spent with most of the greenery outside buried underneath a sheet of white snow, I think we do our students good by bringing some natural green into the spaces where they are asked to mentally and psychologically push themselves. At the end of the day, how much can it really hurt to add a houseplant or two to your classroom anyways? Might as well stick a few more plants in a few more places.