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
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
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
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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