Using Nature to Root Out Indoor Pollution
Imagine how indoor air pollution will be combated in the next century. Are you envisioning elaborate, Space Age machinery controlling what is now one of the top five public health threats? Chances are you’re not thinking of the most probable answer--that nature will provide the cure.
The simple answer to improving indoor air quality? Houseplants, says Bill Wolverton, author of “How to Grow Fresh Air: 50 Houseplants That Purify Your Home or Office” (Penguin, 1997, $16).
Wolverton worked almost 20 years for NASA developing technology that would allow humans to live in a closed environment on the moon or Mars. Through this pioneering research, he discovered that houseplants are the quickest and most effective filters of common, dangerous air pollutants. Those pollutants include formaldehyde, benzene, xylene and ammonia. All cause a number of ailments, such as asthma and allergies, and the broader illness now recognized as sick building syndrome.
Wolverton and his colleagues have placed houseplants in sealed chambers and exposed them to hundreds of chemicals. “We’ve found that plants suck these chemicals out of the air,” he says. “After some study, we’ve unraveled the mystery of how plants can act as the lungs and kidney of buildings.”
Plants clean indoor air in two ways. They absorb pollutants into their leaves and transmit the toxins to their roots, where they are transformed into a source of food for the plant. And they emit water vapors that create a pumping action to pull dirty air down around the roots, where it is once again converted into food for the plant.
“Plants decrease gaseous air pollutants, such as ammonia in the air,” says Bob Phalen, director of the Air Pollution Health Effects Laboratory at UC Irvine. “The downside to this, however, is that moisture in the soil and around pots can lead to mold, and some plants emit allergens and pollen, which can be catastrophic for people with respiratory problems.”
According to Wolverton, it’s talk of mold that has limited the use of plants as air cleaners.
“It’s not plants that give off mold and mildew spores, but the soil. Plants actually reduce molds and mildews in the air,” he says. “Research shows that plant-filled rooms contain 50% to 60% fewer airborne molds and bacteria than rooms without plants.”
Wolverton and his co-researchers developed a solution to the mold issue.
“We’ve created soil-free pebbles that can be used to grow plants in water and eliminate the threat of mold,” he says.
These pebbles will be available in several months, but until then, he suggests people sensitive to mold cover the top of the soil with gravel, which will dry soon after watering.
He is also introducing plant pot systems that contain activated carbon filters, fans and lights that he says can triple a plant’s air cleaning ability.
Plants are especially needed in office buildings where sick building syndrome is common, because of the toxins given off by office machinery and pressboard furniture.
For this reason, Wolverton suggests that everyone have a plant on his or her desk, within what he calls the “personal breathing zone.” This is an area of 6 to 8 cubic feet where you spend several hours on a regular basis.
In the home, this space is near your bed.
“The closer the plant is to you, the better,” Wolverton says. “Even in large, open rooms, a plant within your personal breathing zone really improves the air you breathe.”
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Florist Pat Gosnell of Regal Flowers in Orange knows from experience that plants clean the air.
“We’ve got a lot of houseplants in the front of the store, and customers always remark on how fresh the air is when they walk in,” Gosnell says.
“I like to tell customers that when they’re sleeping their plants are working, taking all the dirty toxins and carbon dioxide out of the air they’re breathing and recycling it into pure oxygen,” she says.
Many common houseplants clean indoor air. Bamboo palm, rubber plant and draceana ‘Janet Craig’ are large choices. Peace lily, golden pothos and Boston fern are good smaller choices.
Outdoor plants, including mums, azaleas, gerbera daisy, cyclamen and tulips, brought in for a short time also clean the air.
Some plants specialize. Boston fern, for instance, removes formaldehyde, and the peace lily removes acetone.
Plants need to be clean and in good health, says Steve Kawaratani, owner of Laguna Nursery in Laguna.
To clean plant leaves, he suggests using a damp rag and not applying any oils or waxes, which can cause the plant to sunburn.
The most important key to a plant’s survival indoors is correct lighting, says Kawaratani, who suggests the shadow test to determine how much light you have in a room.
The best light for most houseplants is diffused light, which casts a shadow on a nearby wall but is not strong enough to heat your hand. If the shadow is very weak, the plant must have a low-light requirement.
“If you stick your hand up in front of the window and it’s hot on your hand, then the sun’s intensity is too high for most houseplants,” Kawaratani says. Place the plant farther away or use blinds to adjust the light.
Completely green plants are more tolerant of low light conditions. Variegated or multicolored leaves require more light because they aren’t as efficient in their ability to photosynthesize.
Some houseplants also require high humidity, which can be created by misting your plants on a regular basis or by putting each pot in a pebble tray that is slightly filled with water. The bottom of the pot should touch the pebbles, but not the water.
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Grouping plants also increases humidity. Keep plants away from heating and air-conditioning drafts, which quickly dry them out.
“Make sure your plants have well-draining containers,” Kawaratani says. “You can’t let a plant sit in water without adverse consequences. As I tell customers, try sticking your foot in a bucket for a week and see how it looks when you finally take it out.”
At the same time, don’t let your plants dry out.
To see if a plant needs watering, pick it up. If it feels light, water it. For large plants, stick your finger into it about half an inch. Water if the soil’s dry.
When watering, let the water wash through the plant or immerse each pot in a bucket of water and let it drink until it stops bubbling. Whichever means you use, thoroughly drain the plant before returning it to its location.
Inspect plants for pests regularly by checking the bottom of the leaves. Periodically hose them off to wash off various pests. Do this outside, in the morning or on a cloudy day.
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10 AIR CLEANERS Many common houseplants make great indoor air cleaners. In his book, “How to Grow Fresh Air,” former NASA scientist Bill Wolverton identifies the top 50 plants for cleaning air. He rates them on their ability to remove chemical vapors, their transpiration rate, how easy they are to grow and how resistant they are to pests.
Some plants are better at filtering air and transpiring than others, but don’t let that discourage you, Wolverton says. If your favorite plant isn’t too efficient, put more of them in your house and office.
Following are 10 plants from his top 50 list. Give them low to medium light, keep evenly moist and fertilize with a well-balanced fertilizer on a regular basis. Pinch back to prevent legginess.
Arrowhead vine (Syngonium podophyllum): This is an easy-to-grow vine-type plant with green-white or green-silver leaves that are long and arrow-shaped when young. Mist frequently and keep pruned. It rarely has pests, but watch for spider mites. Feed monthly with a well-balanced fertilizer.
Bamboo palm (Chamaedorea seifrizii): This bamboo-like palm gives a tropical look to your home. Eventually reaching 6 feet, it is easy to grow and tolerates low to bright light conditions. When transplanting, use a cactus mix, because this plant needs a well-draining soil. Allow soil to approach dryness between waterings. Fertilize with a well-balanced fertilizer every two or three months and keep an eye out for mealybugs, scale and mites, which can be treated with horticultural oil.
Boston fern: This plant’s stiff fronds arch out and then droop downward, making it an excellent hanging plant. Make sure that it receives medium to bright light at the top, or no new growth will appear. Keep plant constantly moist, but not soggy, and feed every watering with a quarter-strength fertilizer. Mist regularly and remove yellow fronds when they appear.
Draceana ‘Janet Craig’: This is one of the best plants for removing trichloroethylene. It can reach 10 feet tall and makes a dramatic statement in the home with its rosettes of broad, dark-green leaves and upright growth habit. Provide bright to medium light, and water when the top inch of soil is dry. Feed every two to three months with a well-balanced fertilizer.
English ivy (Hedera helix): This plant is not easy to grow indoors, but it’s often used in topiaries. Although it tolerates low to bright light, it is susceptible to insects, especially spider mites and thrips. To prevent insect infestation, provide with good air circulation and inspect the underside of leaves on a weekly basis for pests. Mist regularly, especially when the air is dry. Fertilize monthly with a half-strength solution and water when the plant is approaching dryness.
Ficus Alii (Ficus macleilandii ‘Alii’): With its slender green leaves and upright tree-like growth habit, this plant brings the outdoors inside. It is virtually pest-free and will tolerate medium to bright light. It should be allowed to approach dryness between waterings. Fertilize with a quarter- to third-strength fertilizer at each watering, since this plant is a heavy feeder.
Golden pothos (Epipremnum aureum): A vining plant with heart-shaped leaves splashed with yellow or cream colors, this plant is extremely easy to grow. It withstands neglect and is virtually pest-free.
Peace Lily (Spathiphyllum sp.): This pretty plant, with its tropical white flowers, excels in removing a number of toxins, including acetone, benzene, formaldehyde and trichloroethylene. It is a reliable indoor bloomer and grows well in low to medium light. Keep the soil moist, but not soggy and fertilize with a 2-10-10 from spring to fall to stimulate flowering. Watch for scale and spider mites.
Rubber plant (Ficus robusta): Especially good at removing formaldehyde, this stately plant, with its large, round, rubbery leaves, can grow to 8 feet. It is easy to grow and can thrive in low to bright light. Let it approach dryness between waterings and feed with a time-released fertilizer.
Spider plant: This plant was given worldwide attention in 1984 when NASA first released research showing its ability to clean the air. Usually grown as a hanging-basket plant, it sends out thin, arching shoots with a small white flower on the end. Provide it with medium to bright light and water when approaching dryness. Feed with a time-released fertilizer and check for scale.
