Wait a minute! Don’t most plants absorb carbon dioxide and release oxygen?

At one of my favourite grocery stores, the exit takes you right through the floral department. You have to push your laden cart through a gauntlet of kaleidoscopic bouquets and potted houseplants primped with foil wrappers and cute signs for maximum adorableness. Which is fine by me. In the depths of winter, I love a whiff of pungent greenery just before I head into the frigid parking garage with my week’s supply of chicken soup and margarita mix.

But during my last shopping trip, I yanked my buggy to a halt at the sight of a very odd thing–a display of bright green ferns. Their rubbery fronds, splayed in undulating waves, looked freshly snipped from a mermaid’s mane. But it was their emphatic plant tags that had caught my eye. These plants released oxygen!!!!

Wait! What? For one wild moment, I had a crisis of self doubt. I thought all plants did that. Well, at least the ones that indulge in aerobic respiration.

They do. So what really made this plant so special? I had to investigate.

THE FUNDAMENTALS OF FERNDOM

That houseplants can help purify the air in your home is not news. But after doing a little digging, I was surprised to discover that not everyone agrees on how the air really gets purified and which plants do the best job.

A Crispy Wave fern, otherwise known as Asplenium nidus “CW”.

As a fern, Crispy Wave (Asplenium nidus “CW”) is naturally predisposed to do a pretty good job. That’s because, for one thing, it has a lot of leaf surface. More leaf surface, more stomata, the tiny pores on the undersides of leaves where carbon dioxide enters in the process of photosynthesis. That’s why, for instance, needleleaf evergreen trees have a lower rate of photosynthesis than broadleaf deciduous trees.

Ferns, being denizens of the forest and jungle, are also most at home in the shade so they’re undemanding in the sunlight department and can easily feel at home in your home. In other words, they’ll continue to rock that photosynthesis thing even if they’re parked in your living room, thank you very much.

Ferns aren’t the only plants that do a good job of purifying household air, though. In one assessment, 50 houseplants were tested on four criteria:

1. removal of chemical vapours
2. ease of growth and maintenance
3. resistance to insect infestation
4. transpiration rates

These ferns are cute but I’m not sure they’re worth the price, given that it turns out they’re only doing half the work of purifying your air.

The ten plants that best met the challenge included four palms, the rubber plant (Ficus elastica), Dracaena, English ivy, Ficus, Peace lily and, yes, Boston fern. (See the entire list here.)

Still, ferns are notably good at what they do. In fact, a study in which 86 plants were tested proved ferns tops at formaldehyde removal (which can be emitted from plywood, carpets, tobacco smoke and other nasties).

But, as it turned out, green plants in general weren’t the only heroes. That study also proved that the soil microorganisms living in healthy potting soil were actively involved in removing formaldehyde and other toxins from the air, day and night.

THE REAL DIRT ON WHO’S PURIFYING WHAT

So it’s not just about the plants. The microorganisms in the soil work hard to filter the air as well. A NASA study from 1989 (actually mentioned on the website of the company that is marketing Crispy Wave ferns) has done much to herald certain plants as household air purifiers. But, in its summary, it also states that it’s the “plant root-soil zone” that appeared to be the most effective area for removing volatile organic chemicals. “Therefore,” the report continues, “maximizing air exposure to the plant root-soil area should be considered when placing plants in buildings for best air filtration”.

SO WHICH PLANTS OFFER THE BIGGEST PURIFYING BANG FOR YOUR BUCK:

• Chrysanthemum morifolium (Garden mum or Florist’s chrysanthemum)
• Spathiphyllum ‘Mauna Loa’ (Peace lily)

These two houseplants have been proven to remove the top 5 nasties of household air: Benzene, formaldehyde, trichloroethylene, xylene/toluene and ammonia.

But be sure to plant them in an extra wide pot so that your other good buddies, the microorganisms in the soil, can do their unsung but equally important bit, too.