Q: What is the truth about house plants purifying indoor air? Do they or don’t they substitute for air filters? Does living with plants contribute to healthier breathing? Are there particular plants which I should grow to improve the air in my home?
A: How much house plants affect air quality is a wonderful example of the difference between laboratory experiments and the world outside a lab. The first experiments to determine whether plants could clean up air were carried out by NASA. That was back in the 1980s. The idea, of course, was to find ways to provide the best quality air for astronauts on long space missions. The studies were done one chemical at a time, one potted plant at a time, in a sealed Plexiglas test chamber the same size as a compact car trunk.
Having decided that those test results were not necessarily useful even for a space capsule, in the late 1980s NASA built a new test chamber. On federal government property in Mississippi, it was called the BioHome Space Center. The building was a metal box on legs, with dimensions of 16 by 45 feet. The box included a large plant room for testing the effectiveness of plants in cleaning both recycled air and raw sewage. Tests found that people could live comfortably in the sealed environment once the plant system was well established and working.
Other organizations began experiments to duplicate or improve on the research by NASA. They have had generally positive results. On the other hand, by now no one knows how much the air is purified by plants and how much by the microbes which live in healthy potting soil.
A more recent experiment done in Australia attempted to judge the effect of plants on air pollution in the real world. It found that in an office building with sealed windows, three plants per office reduced air pollution enough to eliminate any health risk to people breathing the air.
Still more recently, research evaluations by EPA scientists have criticized most of the experiments on plants and air pollution as being poorly constructed. For one thing, some experiments had no controls against which to measure experimental results. Also, several experiments were carried out under artificial laboratory conditions. In some cases air sampling periods were only five minutes long. Nor did anyone pay attention to doors and windows opening and closing during some of the experiments. Studies done in a laboratory were carried out in sealed boxes far too small to hold even one person. Many studies measured only very high concentrations of pollutants, which were artificially introduced one at a time. The EPA noted that nothing measurable could yet be stated about the effect of plants on polluted air.
The bottom line is that house plants do clean up the indoor air we breathe, but no one yet knows how much. When applied to the real world, lists of the best plants for reducing air pollution mean nothing at all.
Compost pile starter
Q: Does my compost pile need to have some kind of starter added every year?
A: A booster shot of nitrogen will help the microbes in a new compost pile to start digesting the dead plants. The nitrogen can be in any form. A handful of commercial ammonium sulfate fertilizer will do the job. Or chicken manure. Or a shovelful of finished compost from another pile. Or any kind of urine, either straight or diluted.
Once a compost pile is working it needs no extra nitrogen. When a pile is turned or sieved or sorted into finished and unfinished compost, plenty of microbes should remain to start a new pile. All the “green stuff” that goes into a pile is a source of nitrogen. The nitrogen starter on a new pile is designed to help micro-organisms proliferate. Once their populations have reached the billions, no additives are needed; the composting process will perpetuate itself.
Miniature orchid
Q: I bought a miniature orchid a year ago. It has stayed alive, even though it stopped blooming last spring. Will it ever bloom again? It has long bare stems crawling outside the pot. Should I cut them off? I have been using my regular house plant fertilizer for the orchid. Does it need something special?
A: Let’s begin with your last question and work backwards. Orchids will thrive with the same fertilizer as other house plants. If your orchid is still alive and growing a year later, plainly it likes your care. Keep on watering and fertilizing it the way you have been.
The “stems” crawling around are really roots. Because the pot is full of roots, they continue to grow in the only space available – the air. Orchids do not live in soil, as most plants do; they anchor themselves to branches, rocks, or any other stable object. An orchid in a pot uses the pot only as a prop to keep itself from falling over. Often an orchid will have one or two roots growing outside the pot. When the number of aerial roots increases, the pot is full and it is time to move the orchid to a slightly larger pot. Be careful not to give it too big a pot, since that would be an invitation to root rot.
Pull the orchid out of its pot. The roots are big and fleshy and very tough; they do not mind being handled. Cut off any roots which look shriveled and dead. Bend the others around to pack them into the new pot. Pull off any pieces of potting material which are stuck to the roots. There will be no soil. Refill the pot with orchid mix, which is not potting soil. It is composed mostly of woody chunks, either coconut fiber or fir bark. Dump handfuls of the mixture into the pot and pack them down with your fingers. Do not try to be gentle with the roots. They are nearly indestructible, and they like to have the orchid mix firmly packed. Return the orchid to the spot where it has been living and to your usual watering schedule.
Most orchids bloom once a year, most commonly in winter. As long as your miniature is happy, you can expect it to bloom again. A nearby lamp which gives the orchid evening light may hurry the process, but orchid flower stalks develop very slowly. To begin with they look like one more aerial root which starts to tip upward instead of down.
Winter mulch
At last it is time to cover the most tender plants with mulch. Strawberries, garlic, and first-year perennials will all survive in greater numbers if mulched from now until early March. Use any kind of dry organic material which is available. Straw is fine, but so are chopped dead plants (including weeds), pine needles, dead leaves. White nonwoven row cover is an excellent winter mulch, and it is easy to remove next spring. Use one layer of the heavyweight row cover, or a double layer of the standard weight. Tender plants will all appreciate a blanket as temperatures cycle between 50 degrees above zero and 20 degrees below.
House plants can help improve indoor air quality
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