How to grow clean air

We spend a lot of time talking about outdoor air pollution. We worry about the effects that smog and emissions have on our environment, and in turn on our health. It’s an important issue, but are we overlooking something?

Indoors is where we spend most of our time — nearly 90 per cent of it, in fact. In our homes, offices and recreational facilities we’re vulnerable to biological pollutants (like mould, dust and dander) and chemical pollutants from the materials we use to build, heat, furnish and clean our environments. Dangerous chemicals like formaldehyde, alcohols, benzene and other volatile organic compounds (VOCS) can be released into the air from items like carpeting, synthetic materials, resins and common cleaning products like air fresheners. New products can continue to “off-gas” for years after their installation.

We’re often told to “plant a tree” to help the environment. What if we could use that principle indoors as well? Scientists have long known that certain plants can actually improve indoor air quality by removing toxins from the air. But how can you find plants to suit your needs?

NASA researcher Dr. B.C. Wolverton studied the effects of houseplants on indoor air quality and used his findings to create How to Grow Fresh Air: 50 Houseplants that Purify Your Home or Office. The book explains some of the issues and science behind the problem, but also serves as a grower’s guide for selecting and carrying for plants that clean the air. The science isn’t new, but it’s worth a second look considering today’s environmental concerns.

Wolverton tested dozens of plants and assigned them an overall score. How well plants removed chemicals was just one of the criteria. He also considered the transpiration rate (how quickly the plant releases moisture into the air), resistance to pests and bugs and how easy it is to care for the plant. The trick is to find the best ones for your needs — plants that will do the job, but won’t require a lot of attention.

Power plants

Here are Wolverton’s top choices:

Areca palm – Is your home or office dry? This large, feathery plant can release as much as one litre of water over the course of a day once it reaches six feet tall. Mist it regularly and keep it well watered to prevent unsightly brown-tipped leaves and to ward off spider mites.

Lady palm – Tied with the areca palm for first place in the ranks, the lady palm has large fans made up of thick leaves. It’s a slow grower, but easy to maintain. If the leaves get brown tips, a simple trim with a pair of pinking shears will take care of the problem without affecting the natural appearance of the plant.

Bamboo palm – Another tall member of the palm family (reaching a height of six feet), the slender stalks and rich green colour make it a favourite for commercial properties as well as homes. It’s a little more resistant to insects than other types of palms, and highly rated for removing benzene, formaldehyde and trichloroethylene from the air.

Rubber plant – This plant scores well in all categories, and is easy to grow as well as attractive. It won’t need a lot of sunlight, and will tolerate cool temperatures. Wolverton notes that it’s the best plant in the ficus family for removing toxins. The thick, dark leaves provide a nice contrast to more graceful looking palms and ferns.

Dracaena “Janet Craig” – This plant will go the distance: it’s another easy-to-grow favourite, and can last for decades with proper care. The Janet Craig is the best of the dracaenas for removing chemical toxins. It can grow as tall as ten feet, but the “Compacta” version might be a practical choice — it reaches a maximum height of three feet.

English ivy – It seems to be everywhere, but did you know it’s also good at tackling toxins? Let it trail from a hanging basket, or try cultivating it in topiary form. It likes to be misted frequently, and even likes a little outdoor vacation in the summer months.

Dwarf date palm – Don’t be fooled by the name: as an indoor plant this palm can reach a height of over five feet (though it won’t reach that height in a hurry). The plant likes it’s personal space – its fronds can grow up to three feet wide. With its rainforest roots, it can cope well with low lighting conditions.

Ficus alii – This one comes in three varieties: bush (several stems in one pot), braids (two or three stems intertwined) and the standard tree. It’s perfect for a sunroom or bright location as it prefers full sun and semi-sun conditions. It hates drafts, but isn’t prone to bugs.

Boston fern – It’s a little fussier when it comes to maintenance, but this lush plant is the best at adding humidity to the air and removing formaldehyde. It looks attractive in a hanging basket or on a pedestal, but requires frequent watering and misting to prevent it from drying out.

Peace lily – The only flower to make the top ten, Wolverton notes this plant is a must-have when seeking some variety in your indoor houseplants. The lush green foliage is attractive, and it’s one of the few indoor plants to reliably bloom indoors. The lily is good at removing alcohols, benzene and acetone.

Flowering plants don’t tend to score as well as their greener counterparts, but if it’s colour you’re after try the wax begonia, florist’s mum, gerbera daisy, tulips, dwarf azalea and cyclamen. Seasonal plants such as the Christmas cactus and the poinsettia are also good bets.

Other popular plants in the top 50 include the spider plant, the parlour palm, aloe vera, snake plant and the Norfolk Island pine.

What else should you know?

Beyond the criteria ranked in Wolverton’s book, there are a couple of other questions you might want to consider when looking for plants:

Are they pet and child-friendly? Plants that are toxic to humans are often toxic for animals as well (and vice versa). Some plants like English ivy, rubber plants and poinsettias aren’t safe for consumption even though they’re good for the air.

Spider plants, Boston ferns and most houseplant palms are generally safe for homes where they might get the occasional nibble. (See the University of California’s Know Your Plants… Safe or Poisonous? website or talk to your veterinarian for more information).

Where can I put them? Many of the best plants for removing toxins are also some of the largest. For esthetic appeal and optimal growth, choose plants to compliment your space and décor. In addition, be aware that lighting conditions are equally important for indoor plants are they are for your garden. Check out how much light your room gets and match the plants accordingly.

And watch out if you have children or pets around. Large planters may also be a tempting place to dig, and some plants may fall victim to curious shelf-climbers or wagging tails.

Will the plants affect my allergies? In many cases, you can escape pollen allergies by choosing non-flowering plants. However, overwatering can exacerbate another indoor air pollutant and allergen: mould. The Canadian Lung Association warns that mould can grow in the soil and drainage pans of over-watered indoor plants. It recommends limiting the number of indoor plants in the home and keeping them out of the bedroom.

Where will they do the most good? Wolverton recommends placing plants in “personal breathing zones” — the six to eight cubic foot area surrounding us. They’re usually areas where we spend a lot of time, such as in front of the computer or by a favourite chair in the living room. Plants placed in these areas will help increase humidity, remove toxins and suppress airborne microbes.

How many do I need? Some websites suggest as many as 15 to 18 good-sized plants in an 1800 square foot home, but it really depends on the space, environment and exposure to toxins.

How can I prevent insects and other problems? Plants that are more prone to problems simply require more attention to their care. The best way to avoid problems is to follow instructions: ensure proper watering conditions, provide some air flow and remove any dead plant material right away. Read up on the plant to find out about signs (such as brown-tipped leaves) that can alert you to problems. Wolverton’s book also suggests non-toxic ways to deal with pests.

A case of mites or powdery mildew can spread from plant to plant and soon infect your whole collection. Most experts agree that it’s a good idea to isolate any new plants when you first bring them home. Once you’re sure they aren’t showing signs of infestation or problems, they can join your collection.

Research into plants and indoor air quality is still ongoing. While plants alone won’t solve the indoor pollution problem entirely or cure a case of sick building syndrome, they will help create a better indoor environment — in more than just an aesthetic sense.

Photo © Arpad Nagy-Bagoly

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