Can indoor plants really cool a room? Like for real?

It. is. hot.

While I’m writing this, Europe is melting under a heatwave. Trust me, I won’t argue with people who are using air conditioners to survive temperatures of over 40° degrees. I was one of them before I moved to the considerably cooler Sweden. However, it does get me thinking though. The hotter it gets the more air conditioning we’re using which means the hotter it’s going to get. A vicious circle of air conditioned doom.

Cool down a room without air conditioning?

So what alternatives are there? Apart from the obvious, like keeping your shades down and switching off unused electronics, there are also tons of articles out there about how indoor plants can help cool down a room. Seriously? It’s the dream! Imagine for a plant lover like myself to find out that to help save the planet I would have to FILL MY HOUSE UP WITH PLANTS?! Where do I sign up?

I started reading more. Apparently, some plants are better at cooling than others. Aloe Vera, Ficus, Ferns, Snake Plants. While those are all amazing plants, I started to get a bit sceptic, for a very simple reason. I used to have an Aloe Vera in my flat in France and it was still hotter than the center of Mount Doom. Clearly more research was needed, so I started looking for articles that showed some actually proof of how plants could accomplish this magical feat of giving us sweet sweet relief from the heat. When I finally found some that were citing sources, I realised that most of them go back to a certain Dr. Leonard Perry, Horticulture Professor Emeritus, from University of Vermont who in his article “Benefits of using Plants Indoors” says that :

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. 

Dr. Leonard Perry

That’s it. In the entire article, that’s all the information about the amazing cooling powers of indoor plants. That’s all that those endless amounts of blog articles on the subject are based on?

The proper use of plants?

I haven’t been able to find the original USDA estimate that Perry mentions. So this is where my trail ends and all I am left with is… A LOT of questions. Like, what’s the proper use of plants? Is having one or two pots enough or do I need to cover my walls entirely in English Ivy? What type of office are we talking about? And what size room? Does ‘decrease by as much as ten degrees‘ mean it could also not decrease at all? And what on earth does a ten degree Fahrenheit temperature difference mean in Celsius?

Unfortunately, I haven’t found a single shred of proof that buying a bunch of ferns and aloes is going to help any of us tangibly reduce the temperature in our overheated city flats. I’ll reluctantly have to agree with this one plant dude in Kansas who said:

I’d never tell people to come in and buy all these plants it’s going to cool your house because that might work in a laboratory or a scientific experiment but all the other variables of how you live in the practical world, the effect of plants, while positive on your house, is not going to be a cooling of the house by 10 degrees.

Matt Stueck, Vice President of Suburban Lawn and Garden

BUT before we throw the Aloe out with the bathwater, it’s important to point out that while they might not help us cool down all that much, having a nice collection of indoor plants or even a full blown urban jungle still has a lot of other positive effects, such as reducing stress and improving air quality (although I think I might have to research that one next). Also, plants are just awesome sauce and you can never really have enough of them.

All hope is not lost. Just think bigger.

So what do we do about the heat? Turns out, plants might still hold the answer to our sweaty sticky summer nightmares. We just have to think a lot bigger. Once we step outside our own four walls, we find tons of research that shows how turning our cities into greener spaces helps to reduce urban temperatures . Think scorching hot asphalt exposed to the direct sun versus cool spots under shady tree canopies.

A study in Melbourne has shown that urban green spaces, such as leafy tree lined streets are much cooler than places without any plants or trees. Same same was shown in Lisbon. This study in Beijing put actual numbers on how much heat the green spaces could absorb and what the direct decrease in air conditioning demand was.

Here it is, our solution. Plants do indeed cool down temperatures, but not by putting them in a little pot on our window sill, but by integrating them into our urban infrastructure.

So while you’re sitting there, sweating or maybe guiltily cooling down in front of your AC, take a moment and write to your local politician about the importance of investing in greener city policies. And, if you’re lucky enough to own a house, I’d highly suggest you start planting some trees around it.