Reduce Indoor Air Pollution with Houseplants Part 1: Aloe Vera and Peace Lily

By Peggy RudbergSince the late 1970s buildings have been made more airtight to increase energy efficiency. Though the resulting energy savings are good for our wallets, indoor air quality has suffered. The air in our homes and offices may contain from two to five times more pollutants than are found outdoors. And since most people spend the majority of their time indoors, this has become a major health concern.Synthetic materials used in newer construction, furnishings, and electronics, as well as in many cleaners and other common household products, contain volatile organic compounds (VOCs); the most common are formaldehyde, benzene, and trichloroethylene. While limited exposure to these chemicals may not pose health threats, when they come from multiple sources, the cumulative effect can be dangerous.Before you pack your bags and head for the hills, consider the simple addition of houseplants. All plants decrease carbon dioxide and increase oxygen levels in the air during photosynthesis, but they are also capable of a process called phytoremediation, in which they absorb and transfer VOCs and other toxins to their associated soil and microorganisms, which in turn convert the chemicals into usable nutrients.In 1989 NASA released a now-famous study on the ability of houseplants to purify air in closed environments. They tested 20 common houseplants and found remarkable pollutant reduction. They suggest 15 to 18 plants per 1,800 to 2,000 square feet of indoor space.If you like succulents, aloe verais excellent at absorbing formaldehyde and benzene; additionally, juice from the leaves soothes minor skin irritations. The earliest written reference to the plant, in Arabic and dating to the fourth century BC, describes its use as a pain reliever. A member of the lily family, aloe is native to the Arabian peninsula but has been introduced worldwide to hot, dry climates. The earliest-known visual representation of it is from a cave painting in South Africa.Aloe is very hardy, but temperatures below 40 degrees Fahrenheit will cause damage. It prefers a well-drained, permeable soil and bright, indirect sunlight. Water about once every three weeks, allowing soil to dry completely between waterings to prevent root rot. Aloe reproduces with offsets or clones that you can separate, let heal for a few days and replant.If you want a flowering plant, the peace lily(Spathiphyllum“Mauna Loa”) is highly effective at removing all three of the leading VOCs. What appears to be a flower is in fact a leaf bract partially enveloping the spike of tiny flowers on an axis. Despite its name, peace lilies are not true lilies; they are members of the Araceae family, along with Philodendron, another superb air purifier. Imported to Europe in 1824 from tropical Columbia, its minimal requirements have made it a favorite houseplant.Peace lilies thrive in peat-based sandy soil and flower best when slightly root bound. Soak the plant about once a week, preferably with chlorine-free water (let tap water stand overnight) or rain water. Provide good drainage but keep soil slightly moist. In dry climates you may need to mist the plant occasionally. It will wilt when water is needed. It likes medium, indirect light but can survive in darker surroundings. A weak fertilizer during spring and summer growth will promote more flowers. Occasionally removing dust with a damp cloth keeps pores clear and helps prevent pest problems. Propagate by dividing. Note that peace lilies contain oxalates that can harm pets.Look for more air-cleaning houseplant suggestions in upcoming issues of the newsletter.