Indoor Plants & VOCs

Remember when indoor plants were in fashion?

It must’ve been the mid 70’s and I’m picturing my mother in her caftan fussing over the pot plant jungle in the tiled “foyer” of our home - ivy, lilies, ferns, palms and rubber trees, anything and everything green. As kids, we didn’t appreciate the weekly chore of wiping the dust from their leaves to keep them shiny and healthy looking. We certainly didn’t realise that these plants were cleaning our air and helping to keep our growing bodies safe from indoor pollutants and toxins or that by cleaning their leaves, we were helping the plants to balance our home’s internal humidity.

NASA research

It wasn’t until 1984 that a NASA research scientist, Dr Bill Wolverton was able to show that plants don’t just remove carbon dioxide from our air and replace it with oxygen – they actually filter toxic chemicals or VOCs from our air. These days, the levels of indoor air pollution due to moulds, dust and VOCs (Volatile Organic Compounds or chemicals which become gases easily) can be up to 10 times greater than outside pollution.

VOCs such as formaldehyde, benzene, toluene and xylene are found in paints, carpets, computers, cookware, plastics, furnishings, fabrics, cleaning products, air fresheners and personal care products – virtually everything we look at, touch and apply on a daily basis.

Dr Wolverton found that some indoor plants were particularly effective at removing certain VOCs and that these plants were able to convert the pollutants into food for themselves with the help of root microbes. The purpose of Dr Wolverton’s study was to find out which plants could best maintain clean air in potential lunar bases. The tests were performed in sealed chambers and only plants known to grow well indoors were included.

He found that philodendrons and golden pothos (Devil’s Ivy) were best for controlling formaldehyde, gerbera daisy and chrysanthemums ate up the benzene and peace lilies soaked up the TCE (trichlorethylene). A follow-up study by NASA in 1989 found that the houseplants they tested actually removed up to 87% of toxic air in 24 hours. A German study done 5 years later concluded that spider plants were most efficient at reducing formaldehyde levels, English ivy was ideal for cigarette smoke and snake plants (mother-in-laws tongue) dealt well with household cleaning fumes.

Other plants that have been found to readily convert toxic indoor pollutants into food for themselves include: Areca Palm, Rubber Plant, Umbrella Tree, Bamboo Palm, Weeping Fig, Dwarf Date Palm, Australian Sword Fern, Peace Lilly and Dracaena

Low indoor humidity is another cause of illness in the home.

Dry, wintery air can irritate nasal membranes, trigger asthma, allergies and other upper respiratory problems. According to Dr Wolverton, indoor humidity levels between 35 and 65 percent are beneficial to good health and indoors plants will help with this. Plants release water vapour into the air through their leaves which helps to maintain relative humidity – the dryer the air, the more water vapour they return to the air.

Excessive humidity (greater than 70%) can also adversely affect indoor air quality due to mould spores produced by plants. He believed that the solution to this would be to grow plants hydroponically in more humid areas as they don’t produce mould spores because they don’t require soil.

How many plants do I need?

It is suggested that one plant should be allowed for approximately 10 square meters of floor space, assuming average ceiling heights of 2.4m. This means that you need two or three plants to contribute to good air quality in the average domestic living room of about 25 square metres.

Try a mix of plants to get the most out of their different abilities to filter your indoor air. Some plants can cope with very little light, some require indirect sunlight. Try to keep your plants out of drafts as this will reduce their effectiveness.

We are exceptionally fortunate in Australia to have easy access to all of the plants mentioned in these studies.  It seems that for every problem, we've already been given the solution.