Houseplants and Indoor Air Quality | Author: Tom Ogren

Houseplants and Indoor Air Quality

Houseplants can be the source of cleaner air, but they can also be the exact opposite.

There are two main concerns with indoor plants, insects, and VOC's.

Insects? Yes. Any houseplant that does not thrive will eventually get infested with insects, especially mealy bugs, aphids, whiteflies, scale, or spider mites. All of these insects can quickly explode in numbers and can present a serious allergy problem. Insects shed old skin and other parts and this insect dander is very allergenic.

Insects also produce large amounts of feces, called "honeydew," and on this rich organic material mold quickly grows. The mold then produces reproductive mold spores, and these spores become airborne inside the house. Mold spores are of course quite allergenic.

The answer to insects is to keep them healthy. First we should only use houseplants that are well adapted to actually growing inside the house. These plants should get the kind of light they need. Plants that do not get the light they need will get buggy. We must also see to it that our houseplants are well fertilized. Lack of fertilizer will eventually result in a plant that is weak and that will then be attacked by insect pests. I like time-release fertilizers for all houseplants. In addition to time-release fertilizers I also like to use some water-soluble fertilizers too, at least once a month.

Houseplants should be kept clean too. Often dust will land and stick on the leaves and unless they are washed clean on a regular basis, houseplants can be regular dust piles. It is always a good idea to wipe down the leaves of houseplants with some clean water and a sponge. It is a good idea to add a tiny bit of dish soap to the water when you wipe them down, a teaspoon to a gallon. Use lukewarm water. The soap will help make the leaves cleaner, and it discourages insects.

If you find insects on a houseplant, take it outside, put it in the shade, and spray it thoroughly with a mix of dish soap and vegetable oil. Use several tablespoons of each to a gallon of warm water. Spray the plants, soak them every day for a week and if this doesn't get rid of the bugs, then consider dumping them. If the plants are valuable or you just can't bear to part with them, add some neem oil to the above insecticide mix and spray them with this several times.

Sometimes to kill scale on a plant I will pour some vegetable oil in a cup and then just brush it on the scale with a small paintbrush. In very few cases does the oil damage the leaves of the plants, and it will smother the scale. This also will work with mealy bugs.

Do not bring buggy plants back into the house!

Even after you get rid of the pests on the plant, before you return it to your house you need to ask why was it that it got buggy in the first place? Is the light too weak? Is the air in the house too dry for it? Have you been neglecting to feed it enough? Has it been kept too dry? Too wet? Is it too cold inside? Too hot? Whatever the answer, you'll need to change something in order to get it to thrive.

Make a habit of looking over the leaves and stems of all your houseplants on a regular basis. Look on the stems for scale. Look under the leaves for other insect or mite pests. Spider mites thrive in hot weather. Whiteflies thrive in cool weather. One of the best ways to control spider mites is to frequently wash down the plants.

Dander from spider mites is especially allergenic and any plant that continues to get infested with mites ought to be tossed.

VOC's and houseplants?

All plants release volatile organic compounds into the air. Often these are described as "biogenic emissions." Some plants release only a small amount and consume much more than they release. The ones to worry about are the plants that release more than they consume. Chiefs among the plant-produced VOC pollutants are carbon monoxide and ozone. Both of these are primary elements of smog. They're not something you would want in your house. Other VOC gases often of allergy concern inside houses (but not necessarily produced by plants) are formaldehyde, benzene, xylene, toluene, ammonia, acetone, methyl alcohol, ethyl acetate, and trichlorethylene.

Ficus trees. Ficus enjoy a good rating in the OPALS scale because they release so little airborne pollen. Unfortunately, Ficus, and especially the common houseplant tree, Ficus benjamina, they are high emitters of VOC's. Does this mean we should not use Ficus benjamina as a houseplant?

Yes, that's exactly what it means. At any rate, these often fail to thrive in houses since most household light is too weak for them and most household air is too dry. They will often be infested with spider mites or other insects and these will just add to the VOC problem. VOC's are not good for people with allergies and will aggravate existing allergies. Actually, VOC's are not good for anyone.

Which plants are VOC consumers?

Some years ago NASA scientists discovered that certain plants can remove volatile organic compounds (VOC's) from the air. The gases studied included formaldehyde, benzene, xylene, toluene, ammonia, acetone, methyl alcohol, ethyl acetate, and trichlorethylene. The plants listed below are said to be quite effective at removing indoor pollutants. Please keep in mind though that they must be growing healthy and they must be kept bug free in order to work. : Dracaena, Golden Pothos, Red Emerald Philodendron, Dumb Cane, Schefflera, Wax Begonia, Snake Plant, Norfolk Island Pine, Dracaena, Dendrobium and Phalaenopsis orchids, Spider Plant, Arrowhead Plant (Syngonium), Dwarf Banana (Musa), and Chinese Evergreen (Aglaonema) Also recommended for cleaning indoor air were Rhapis, Chamaedorea and Phoenix Palms, but it is important to note here that only female palms should be used. You don't need extra palm pollen in the house. In addition, also recommended for cleaning indoor air were potted chrysanthemums and Gerbera Daisy, but I do NOT recommend these as houseplants. They have high light requirements and will not thrive in most houses, and they can cause contact skin rash. Their pollen (they're ragweed relatives) is highly allergenic. Better to keep the mums and Gerbera daisies outside.

Also NASA recommended as an effective air cleaner plants was Peace Lily, or Spathe Flower, but I do NOT recommend these as houseplants either. They also can cause skin rash and when in bloom they too shed pollen that is allergenic.

It is always a good idea to let houseplants dry out a little bit between watering. This gives the roots a chance to get more air and it also discourages the growth of molds in the soil. When you do water houseplants it is wise to soak them thoroughly rather than give them just a little bit of water each time. Always use water that is luke- warm, at least at room temperature.

About the Author

The author, Thomas Leo Ogren, is an internationally recognized expert on plant sexuality as it relates to human health. He is author of Allergy-Free Gardening, and also of Safe Sex in the Garden. His work has been reviewed in many publications including Alternative Medicine, Garden Design, Women's Day, Earth Island Journal, Wild One's Journal, New Scientist, Landscape Design, Pacific Horticulture, the London Times, and Garden Gate. He has made nu

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