If you grew up in the suburbs, you recognize it immediately: the sweet, sharp smell of someone mowing¹ a lawn or ballfield. As it wafts² into your nostrils³, it somehow manages to smell exactly like the color green. But what are we really smelling when we inhale⁴ that fresh-cut grass scent⁵? And why do we like it so much?

 

Chemically speaking, that classic lawn smell is an airborne mix of carbon-based compounds called green leaf volatiles, or GLVs. Plants often release these molecules⁷ when damaged by insects, infections or mechanical forces -- like a lawn mower⁸.

 

Plants manufacture slightly different forms of GLVs depending on what's happening to them, said Ian Baldwin, a plant ecologist and founding director of the Max Planck Institute for Chemical Ecology in Jena, Germany. In a 2010 study published in the journal Science, he and colleague Silke Allmann, of the University of Amsterdam, found that tobacco leaves punctured⁹ and rubbed with insect saliva¹⁰ released a different bouquet¹¹ of volatile⁶ compounds than leaves that had been poked¹² and brushed with water.

 

GLVs are small enough to take to the air and float into our nostrils. In some cases, they can be detected more than a mile from the plant where they originated. Other species, such as insects that eat plants and the predators¹³ that eat those insects, are extremely sensitive to different GLV aromas¹⁴. For instance, Baldwin and Allmann discovered that predatory Geocoris bugs¹⁵ are attracted to the GLVs released by plants chewed on by a pest called the tobacco hornworm. In other words, the specific smell of the besieged¹⁶ plants indicates to the predators that a snack is nearby.

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