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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Greenhouses, Air pollution

We are installing a greenhouse (8x8 ft.) soon and there is some disagreement as to whether it is o.k. to smoke cigars inside. Is there definitive research on the effects of tobacco smoke and incidence of tobacco mosaic virus or other ill effects, other than the health ones, that is?


The effects of tobacco smoke on growing plants is the stuff of many science fair projects (like this example), most of which determine that the smoke stunts plant growth.

As for tobacco mosaic virus,University of Connecticut Integrated Pest Management has information on how to prevent this disease: TMV is spread readily by touch. The virus can survive on clothing in bits of plant debris for about two years, and can easily enter a new plant from a brief contact with a worker's contaminated hands or clothing. Tobacco products can carry the virus, and it can survive on the hands for hours after touching the tobacco product. Ensure that workers do not carry or use tobacco products near the plants, and wash well (with soap to kill the virus) after using tobacco products. Ensure that workers wear clothing not contaminated with tomato, tobacco or other host-plant material. Exclude non-essential people from greenhouses and growing areas.

University of California, Davis and Washington State University Extension concur with this information.

For general information on the toxins and irritants and added hazards of cigars in particular, see this information from the National Cancer Institute. It takes longer to smoke a cigar than a cigarette, so the duration of plant (and human) exposure to pollution is potentially longer as well.

Unless there is a compelling reason to smoke cigars in the greenhouse, I would avoid it, as it is not beneficial to the plants (or the smoker, of course) and more than likely will be detrimental.

Date 2017-07-18
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Plant Answer Line Question

Keywords: Rosa, Fragrant flowers, Air pollution

I wonder why my roses have lost their fragrance. My 'Double Delight' roses used to have a good smell, and now the flowers are bigger and there is no fragrance.


It does seem mysterious that a once-fragrant rose should lose all fragrance. There are many factors which might cause the perceived lack of scent. According to The Graham Stuart Thomas Rose Book (Timber Press, 1994), rose scent itself is complex, and is composed mainly of geraniol along with many other substances. It is mainly released from tiny cells on the surface of the petals: "Scent is produced mainly in the petals and is given forth when the growth of the flower and the atmospheric conditions are right. From this it will be seen why double roses have more volume of scent than singles [...] scent is especially apparent in most flowers when the air is neither too cold nor too hot [...] In extreme conditions, such as wilting, extra scent may be released [...] Usually the best fragrance is obtained from a newly opened flower growing on a healthy, well-established plant on a windless day when growth is exuberant [...] we may expect fragrance to be at its best on a day when the air is warm and moist rather than dry, when the plant will be functioning well. It is not that moist air conveys better than dry, but that the plant is giving it forth in greatest quantity."

From the above, you may want to consider the following

  • When you discovered the rose had no scent, were the atmospheric conditions optimal for the release of scent?
  • If scent is most prominent on healthy plants, are there any underlying reasons (pests, diseases, cultural problems such as overwatering, poor soil, etc.) the plant might not be at its strongest?

Other things to consider:
Environmental pollutants affect not only our sense of smell, but the fragrance emitted by flowers, as this 2008 University of Virginia study describes:
"'The scent molecules produced by flowers in a less polluted environment, such as in the 1800s, could travel for roughly 1,000 to 1,200 meters; but in today's polluted environment downwind of major cities, they may travel only 200 to 300 meters,' said Jose D. Fuentes, a professor of environmental sciences at the University of Virginia and a co-author of the study. 'This makes it increasingly difficult for pollinators to locate the flowers.'

The result, potentially, is a vicious cycle where pollinators struggle to find enough food to sustain their populations, and populations of flowering plants, in turn, do not get pollinated sufficiently to proliferate and diversify."

Another thing that you might ask is whether your rose was grafted, and perhaps you are getting a different rose coming up from the graft. The loss of fragrance and the different appearance of the flowers makes me wonder if this could be what is happening.

Date 2017-05-06
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Plant Answer Line Question

Keywords: House plants, Air pollution

I would like to grow plants in my dorm room to improve the air quality. Which plants are most effective?


There was a NASA study on houseplants and indoor air quality in 1989, and this link from University of Minnesota Extension refers to it, as well as the list of plants which appeared to have the greatest effect. The study has to some extent been disputed and/or discredited.

The Environmental Protection Agency has useful guides to maintaining good indoor air quality, one aimed at health care professionals, and one for the general public.
Here are excerpts from each:

"Recent reports in the media and promotions by the decorative houseplant industry characterize plants as 'nature's clean air machine', claiming that National Aeronautics and Space Administration (NASA) research shows plants remove indoor air pollutants. While it is true that plants remove carbon dioxide from the air, and the ability of plants to remove certain other pollutants from water is the basis for some pollution control methods, the ability of plants to control indoor air pollution is less well established. Most research to date used small chambers without any air exchange which makes extrapolation to real world environments extremely uncertain. The only available study of the use of plants to control indoor air pollutants in an actual building could not determine any benefit from the use of plants. As a practical means of pollution control, the plant removal mechanisms appear to be inconsequential compared to common ventilation and air exchange rates. In other words, the ability of plants to actually improve indoor air quality is limited in comparison with provision of adequate ventilation."

"Over the past few years, there has been some publicity suggesting that houseplants have been shown to reduce levels of some chemicals in laboratory experiments. There is currently no evidence, however, that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices. Indoor houseplants should not be over-watered because overly damp soil may promote the growth of microorganisms which can affect allergic individuals."

All that being said, houseplants can, at the very least, provide an aesthetic improvement to a room, and as long as you are careful not to overwater, they shouldn't hurt air quality.

Date 2018-03-14
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May 23 2018 14:32:42