How to grow fresh air
January 8, 2015 10:54 AM   Subscribe

Why you should water your house plants more often... Kamal Meattle describes how common houseplants can result in measurably cleaner indoor air. His work stems from earlier NASA research by Bill C. Wolverton who first investigated how to grow air in a space station before researching the indoor environmental impact of plants themselves.

Buildings and houses are increasingly sealed off from outside air in order to conserve energy from heating and cooling. While this saves energy, it also prevents air exchange from inside to outside and as a result we live in increasingly closed-off environments. Off-gassing from carpets, paints and other household materials accumulate within the home with no means of escape. In the extreme, this can cause Sick Building Syndrome, with symptoms such as headaches, dizziness, nausea, and eye nose or throat irritation. But what is a company to do? The answer: Plants!

In heavily polluted New Dehli, Karma Mattal, CEO of Paharpur Business Centre, grows 400 plants in his office building's greenhouse to help clean its indoor air.

Karmal did this because of the NASA clean air study which showed how plants can remove pollutants such as formaldehyde, benzene, ammonia, alcohols from carpet off-gassing and of course carbon dioxide. The plants do not store these pollutants but draw them into their roots where bacteria in the soil break them down into harmless byproducts.

Bill C. Wolverton was instrumental in this research and published his findings in his book, How to Grow Fresh Air.

Want to know which plants to buy? Read this list of plants which include such beauties as the Boston Fern, Areca Palm, English Ivy and Mother-in-Law's Tongue (heh). Most of these plants are fairly inexpensive and available at your local nursery. But be careful which ones you get as some plants are poisonous to pets.

And don't forget to water and sun your new indoor friends!
posted by St. Peepsburg (27 comments total) 51 users marked this as a favorite
It makes perfect sense that having houseplants would make your indoor air cleaner. However, this doesn't account for the fact that I have the blackest of black thumbs and manage to decimate any and all houseplants given to my care. (Yes. I've managed to kill even the hardy ones. )
posted by PearlRose at 11:02 AM on January 8, 2015 [1 favorite]

"Grow air"

Love it.
posted by gwint at 11:14 AM on January 8, 2015

Our house plants do ok most of the time. The problem we have is the cats believing we've given them yet another litter box.
posted by spikeleemajortomdickandharryconnickjrmints at 11:18 AM on January 8, 2015 [1 favorite]

I know it was meant metaphorically, but if you already water your house plants appropriately, do not water them more.
posted by snofoam at 11:19 AM on January 8, 2015 [15 favorites]

I thought this was a great idea too, but I learned that they have a staff of people there who hand-wash each leaf of those plants on a regular basis. Apparently this step is important to maintaining indoor air quality and the ability to produce oxygen. Whether that's true or not I don't know. In any case that may be feasible given labor costs in India, but I think it would be more difficult to do in Europe or North America.
posted by Pararrayos at 11:20 AM on January 8, 2015 [1 favorite]

Yeah I meant it for lazy SOBs like me who only remember to water a plant when it is on the brink of death and begging for a swift demise...
posted by St. Peepsburg at 11:34 AM on January 8, 2015

My house gets so little sunlight that I have almost given up on keeping any houseplants. When I moved into this house back in 2006, I had about 15 plants. They have all died. The specifically low-light plants I have bought since died as well. I'm down to a single plant, an aloe vera, which is the third one I've had, as both the aloe I had when I moved in and the aloe I bought to replace it died. I do have quite a nice garden every summer (two actually: one in front and one in back), but otherwise must breathe the air of my city home as I find it.
posted by orange swan at 11:38 AM on January 8, 2015

I need a place I can go where the plants are regularly washed and watered, yet also has sunlight and CO2.
posted by pashdown at 11:40 AM on January 8, 2015

Any recs for cat-safe plants that can survive being nibbled on by cats?
posted by longdaysjourney at 11:43 AM on January 8, 2015 [1 favorite]

I'm pretty poor with houseplants too. I've got a spider plant I bought last fall, and a lot of it has died off. I'm hoping if I start paying more attention I might be able to do something about it.

Oddly, though, on a whim, I planted a handful of seeds from a store-bought lemon last summer in a disused pot outside. When the weather started getting cold, I took the two healthiest seedlings and put them in small pots, which have sat on the kitchen windowsill. Since then, they've both over doubled in size, each have graduated from small to large leaves, and are still clearly going strong, even with the short NW days limiting their light.

Perhaps the lesson here is the fact that because of their location, I'm making sure the little lemon seedlings are watered all the time and paying attention to them. The spider plant gets a lot less attention.
posted by evilangela at 11:43 AM on January 8, 2015 [1 favorite]

This stuff gets extraordinarily frustrating when you try to pin down facts and numbers and see if the people in the follow-up studies did actual Science!(tm).

Apparently this step is important to maintaining indoor air quality and the ability to produce oxygen.

I've had very little luck finding out how much carbon dioxide one houseplant scrubs out of indoor air and how much oxygen it provides.

Also, Wolverton got the best results integrating a carbon filter and fan:

Results of the activated carbon-houseplant studies are shown in Figures 3 and 4.
Although this research effort was not part of the NASA-ALCA two-year study, it is an essential component in the development of an indoor air pollution control system with plants to remove high concentrations of pollutants such as cigarette smoke and organic solvents. This biological system also utilizes plant roots and their associated microorganisms to purify indoor air; it differs from the potted plant study reported here in that a fan is used to rapidly move large volumes of air through an activated carbon filter. This filter adsorbs air pollutants and holds them until the plant roots and microorganisms can utilize them as a food source; therefore, bioregenerating the carbon.


In an unpublished 2006 study, Wolverton tested a small fan-assisted planter/air filter inside a travel trailer that had been used as temporary housing for displaced Hurricane Katrina victims.

Wolverton's research shows that plants do a better job clean the air when you blow contaminated indoor air across or through a carbon filter while using plants roots to clean the crap out of the carbon filter. People invoking him always leave out that part of his recommended setup. (He looked at more generic setups without a fan and filter, as well.)

So this doesn't necessarily that when you put 3-4 houseplants in a generic cubicle or living room that it does anything meaningful for indoor air quality under these conditions. Or how many houseplants you need for a given scenario.

Which is what everyone is doing; they're leaving out the fan and carbon filter.
posted by sebastienbailard at 11:44 AM on January 8, 2015 [8 favorites]

sebastienbailard:blow contaminated indoor air across or through a carbon filter while using plants roots to clean the crap out of the carbon filter.
Thanks for that essential, missing info. (Another damn I ARE SCIENS RITER! case...)

I can't figure out the arrangement, and a quick look through the PDF you referenced didn't reveal it to me. How are the roots and carbon filter associated? Blowing air across roots will dry them out; putting the filter right on the ground means no air flow... what's the setup look like?
posted by IAmBroom at 12:03 PM on January 8, 2015

Ctrl-F "Cats"

Yup, came to ask those question too. I don't want a list of what plants are good for my house. I want a list of plants that will *survive* in my house. I'll put $40 down, this week, on plants that will: not be able to be knocked off shelves, survive with little light and no direct sunlight, not poison my cats, and survive getting batted around.
posted by rebent at 12:10 PM on January 8, 2015 [1 favorite]

One of my very first houseplants was this Fittonia that by god, I loved. It looked so lovely in the frosted blue plastic pot I'd gotten for it (which I'm sure was stylish at the time), it tolerated my oafish attempts at care without withering away into nothing, and it made me feel like a real, live grown-up to be somehow keeping a plant alive on my own. I liked it so much that I took it with me when I moved from FL to Chicago for an internship one summer, but tragically, on the drive back home I left it on a table in the hotel room I stayed in overnight. I like to think that maybe the next guest took it with them and perhaps forgot it in ANOTHER hotel room, and that that continues to happen, and that Felix Fittonia is still out there somewhere having magical plant-based adventures as he roams the world ...
posted by DingoMutt at 12:15 PM on January 8, 2015 [6 favorites]

I can't figure out the arrangement, and a quick look through the PDF you referenced didn't reveal it to me. How are the roots and carbon filter associated? Blowing air across roots will dry them out; putting the filter right on the ground means no air flow... what's the setup look like?

Dunno. doesn't finish loading for me, and trying to reading google's mangled cache of it makes my brain squeak.

Wolverton has two sets of results; really good results with carbon filter+fan+plants, and half-decent-ish results with just houseplants. I don't have the background to say how significant his latter results are.

The last time I ran into this, I was trying to figure out how many plants you need to improve your indoor air oxygen, and does adding a dozen houseplants to a living room actually do anything?

I failed to figure this out.
posted by sebastienbailard at 12:29 PM on January 8, 2015

Kamal's rule of thumb was 4 plants per person; if you click on the "list of plants" link wikipedia quotes 1 plant per 100sqft.
posted by St. Peepsburg at 12:39 PM on January 8, 2015

And where did he get those numbers - does he have a useful experimental setup and statistical analysis backing him up? Where did wikipedia get those numbers? Houseplants exhale CO2 at night, does that make a difference and do you see a meaningful net gain from a houseplant in a room?

It's all vapor.

I need to read the study mentioned in the national geographic writeup:

... Not everyone is convinced. "I certainly would not rely on plants to clean indoor air...To get them to work, you'd need too many plants," says John Girman, former senior science adviser at the U.S. Environmental Protection Agency's Indoor Air Division. He says a 1,500-square-foot house would need 680 plants to duplicate NASA-like benefits, and the result would be "an indoor jungle" with moisture problems.

posted by sebastienbailard at 12:47 PM on January 8, 2015 [3 favorites]

I have a peace lily at work. Its needs are simple, oxygenates the room, can be used to fend off an attacking giant in a pinch.
posted by fifteen schnitzengruben is my limit at 1:06 PM on January 8, 2015 [7 favorites]

Are there houseplants that won't get infested with flies/gnats/tiny flying things? Apparently it's possible to repot plants with sterile soil to save the plants while eliminating the infestation, but ain't nobody got time for that.*

* OK, lots of people probably have time for that. I just don't wanna.
posted by asperity at 3:25 PM on January 8, 2015 [3 favorites]

Wikipedia on the NASA clean air study and a Practical Asthma Review article on more studies. The soil bacteria and associated roots likely plays a major part in any results.
posted by Brian B. at 5:25 PM on January 8, 2015

If you let the top little bit (inch?) of the potting mix dry out, it is supposed to break their annoying little life cycle. I'm trying it with a plant of mine that was pumping out those horrible little flies like a factory, and I *think* it's working.
posted by thylacinthine at 5:34 PM on January 8, 2015

Seconding. All you people with gnat and plant death problems, stick your finger into your plants' soil every so often. A little beyond your first knuckle. If it's moist down below and dry up on top, perfect. Let it be. If it's dry all the way down, water it until water comes out the bottom then leave it for a while. If you feel the soil regularly you get a sense for how much water your plant and soil mix needs. There's nothing fungus gnats love more than soil that's wet all the time, because then they have unlimited egg-laying and larvae-feeding real estate. There's nothing that plants love less than soil that's wet all the time, because then their roots can't breathe.
posted by Dr. Send at 6:37 PM on January 8, 2015 [1 favorite]

Now I've got to go dust the damn plants.

Thanks for reminding me.
posted by BlueHorse at 10:03 PM on January 8, 2015 [2 favorites]

A few months ago I did some research on plants that were good for the air versus bad for cats. I ended up going with the bamboo palm. It is on NASA's list and is thriving despite the feline presence.
posted by fuse theorem at 6:33 AM on January 9, 2015

OK black thumbs and cat people. Here is the deal with plants.

1) Watering: You're more likely to be watering them too much, not too little. Unless the instructions on a plant specifically call for more, you water it whenever the top 1-2 inches are dry (3-4" for succulents, bone dry for a certain select plants)-- not on a regular schedule, because conditions vary. Look at your plants. Get to know them. It's fun to spot new growth.

2) Sunlight: Full sun means 6 hours of direct sunlight. This is often the issue with scraggly, sickly plants. Even shade plants need enough light that you could read comfortably. Don't forget to rotate each side towards the sun as time passes.

3) Cats: most plants that are poisonous to cats, what they really mean is that your cat will get diarrhea or will vomit. They'll learn their lesson, maybe, but they won't die. NOT LILIES. STARGAZER LILIES WILL KILL YOUR CAT. Callas are fine.

4) Cats, part two: on top of your layer of dirt, add a 1-2 inch layer of decorative pebbles. It will look nicer than dirt, and the cats will lose interest in making it their litter box.

5) Cats, three: they're gonna nibble. Get used to it.

No go forth and liberate tons of plants from your garden center! If you kill them, try again until you don't. Like anything, house plants need a little bit of practice before you are a pro. Good luck!
posted by BuddhaInABucket at 9:50 AM on January 9, 2015 [8 favorites]

I remember watching Kamal Meattle's TED talk about this a couple of years ago and thinking it was mostly bs. This io9 summary puts it in perspective: "To be safe, don't get into an airlock without bringing about seven hundred potted plants with you."

And if I thought there were significant amounts of benzene, formaldehyde, trichloroethylene, xylene or toluene, or ammonia (or any other solvents) in my house, I would

a) Move my kids somewhere else
b) Have someone test the air
c) Deal with the problem at the source
d) Re-test before moving back in.

Without getting into a discussion about whether or not there are safe levels of exposure to any of these, I really don't think houseplants are going to remove significant amounts of these chemicals from the air.

We have lots of houseplants. Continuing BinaB's advice: 6) between waterings, leave them alone. They like that.
posted by sneebler at 6:47 PM on January 9, 2015

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