Smart Stuff with Twig Walkingstick: Someone Cut the Grass (for the Week of May 20, 2007)

May 14, 2007

Q. Dear Twig: Why does cut grass smell like it does?

A. Because of chemicals called volatile organic compounds, or VOCs. In particular, because of a VOC that goes by a cool-to-say name. Scientists say cis-3-hexenal ("sis-three-HEK-suh-nuhl") gives just-mowed grass its fresh, "green" smell.

Grass, trees and other plants normally give off VOCs. But when a plant gets hurt — say, a bug eats a leaf or your dad mows the lawn — the plant puts out even more VOCs. Hundreds of times more, say scientists in Australia. These VOCs vaporize ("VAY-puh-rize"; turn into gas) quickly. They spread in the air. They go up your nose. Your brain takes a whiff and says, "Who cut the grass?"

In fact VOCs help a hurt plant to heal. They seal wounds and stop infections. And their smell attracts bugs that eat bugs that eat leaves. The bug-eating bugs eat up leaf-eating bugs — bugs that maybe caused the hurt. The plant gets protected. It gets to get better.

The smell smells green and keeps plants that color!

Twig

P.S. Japanese scientists have shown as well that the cut-grass smell makes people feel better!

 

Notes: Sources included "Plant Production and Emission of Volatile Organic Compounds, BioScience, June 1997; "Lawn Clippings May Help Make Smog," http://www.abc.net.au/science/news/stories/s1252461.htm; Environment Canada (VOCs), http://www.ec.gc.ca/nopp/voc/en/bkg.cfm; and "Prevention and/or Recovery Effects by Green Odor(s) on Fatigue and Green-odor-responsible Brain Regions as Revealed by PET" (the study on human effects by Japanese scientists) in Chemical Senses, 2005. Also check out http://www.chm.bris.ac.uk/motm/hexenal/hexenalh.htm.

About this column: "Smart Stuff with Twig Walkingstick," a free public service of The Ohio State University College of Food, Agricultural, and Environmental Sciences - specifically, of the Ohio Agricultural Research and Development Center (OARDC) and Ohio State University Extension, both part of the College - is a weekly column for children about science, nature, farming and the environment. The reading level typically rates at grades 3.5-4.5. For details, to ask Twig a question, and/or to receive the column free by mail or e-mail, contact Kurt Knebusch, CommTech, OSU/OARDC,1680 Madison Ave., Wooster, OH 44691, knebusch.1@osu.edu, (330) 263-3776. Online at http://extension.osu.edu/~news/archive.php?series=science.

Author(s): 
Kurt Knebusch