Using plants as natural humidifiers and air filters

I live in a pretty cold place, at least in the winter, and heat with wood, so my air quality can get pretty suspect in the wintertime. I loathe electric humidifiers - the electricity use, the cleaning, the worry that I'm not cleaning them well enough. I keep a pot of water on the woodstoves, but that's not really cutting it, humidity wise. So I'm playing with the idea of keeping plants in the house to keep the humidity up.

I already have a bunch of houseplants - mostly spiders, pothos, aloe and rubber (which I know don't add too much to the humidity), but I'm looking for some options on plants that could make a significant difference to the air quality. I know Pothos are known for being good filtering plants. What plants are good respirators (is that the word I'm looking for)? And what kind of density am I going to need to make a difference in my 1800 sq ft home? Or maybe I need to think about it on a room-by-room basis?

I found some pretty nice articles about this topic: research paper with a very helpful chart about which indoor plants do what. On how many plants are necessary to have an effect, I have found conflicting views on this, the results from a study conducted in India about how plants affect indoor air quality, they used around 1200 plants in a 50,000 square foot building which means the density of plants was 0.024 plants per square foot. In your case that would be about 43 or 44 plants because you can't have 43.2 plants. Then at another site they recommend around 15 plants for 1800 square feet which is about a third of what was in the results from the study conducted in India.

For increasing humidity, the first research paper recommended:
-acea palms
-bamboo palms
-boston fern
-gerbera daisy
-kimberly queen fern
-peace lily

The best plants for air quality (9 ranking) in the first research paper are:
-bamboo palm
-boston fern
-dwarf date palm
-english ivy
-florist's mum
-gerbera daisy
-kimberly queen fern
-rubber plant

One fact that I thought was pretty interesting while looking this up was that many plants release negative ions into the air which attach to allergens, similar to how modern air purifiers work. Nature had it figured out before we did!

Iam not aware of any study that makes a good case for better indoor air quality with interior plants. Such studies should be showing the before and after effects of measured indoor air pollutants and it seems that the effects of realistic amounts of houseplants do not effect the air enough to measure much of a difference.

If you want to measurably improve indoor air, introduce outdoor air.

Houseplants probably pose a greater risk of making the indoor air worse. I probably have too many plants in my house which drives the interior humidity into the danger zone. Here is a picture of visible mold, mildew and failing paint that is noticeably increased when I bring my houseplants inside for cold weather.



Window condensation is a visible indicator of too much interior humidity. The same thing is probably going on to some degree inside of my walls.

Woodstoves will certainly keep things dryer but it also suggests your building envelope could use some serious weatherization. Most building experts recommend keeping interior humidity in the 30-40% range during cold weather to prevent hidden condensation.

Dave - Thanks! That's the kind of thing I was looking for...

Brian - I do take your comments to heart, and one thing I need to be aware of is how to adjust between the seasons - I won't want so many plants in the house during the more humid summer months, so I'd probably want some that would do okay outdoors during that time. But here in Maine, dryness is a pretty serious issue in the winter, and where I live, on a windy hilltop, too much humidity is very seldom a problem. Right now the humidity in the house is around 20%, and my family wakes up with dry mouths and nasal passages without some kind of humidifier. That kind of dryness can lead to more sickness in flu season, something I'd very much like to avoid.

Right now, the outdoor air is around zero farenheit, and you're right, our 224-year-old farmhouse could definitely use some weatherization. We've started on insulating the basement sills, and have plans to do more, but there's only so much money and time for those projects.

Do you have any links that show a negative impact on air quality when using houseplants? Because if that's the case, I'd certainly like to know. I've only really heard good things about utilizing plants indoors...

Yes, 20% is getting too low. Just want people to be aware that adding plants to homes that already maintain relatively high levels in the 40-60% range are likely to increase risk not alleviate it. While I cant readily offer any sources, excess moisture is a well known indoor air pollutant.

Iam willing to bet that this overly dry air problem only happens in extreme cold weather and times of high woodstove use. Weatherization is possibly a better main solution to the problem. It doesnt have to be expensive. It mostly involves air-sealing work and I would bet even more that your attic floor/upper level ceiling is an area ripe for major cost-effective improvement.

Quantity and size of the plant containers with accompanying soil moisture levels seem more likely of solving your main problems than Flora species or variety. Sure plants can help in times like this but wouldnt you also rather be burning less energy and chopping+shlepping less wood?

So far, I haven't found negative air quality things, just common sense stuff: don't eat mushrooms that may grow in household plant pots and don't eat your pretty household plants.

Also, there are a few other reasons to bring plants indoors, looking at and being around plants aids the healing process, increases concentration, happiness, health, learning, and more.

i find my plants require additional humidity via a cold air humidifier to be happy
also pests like spider mites thrive in a drier environment

Perhaps an indoor waterfall?

Done correctly it could be attractive and pleasant sounding as well as adding humidity.