Why Does Fresh Cut Grass Smell That Way?

April 27, 2022

A lawnmower cutting grass.

There’s more behind the smell of freshly cut grass other than it is a pleasant aroma to most people. The scent is actually the plant giving out its own distress signal that something has gone terribly wrong. But who is the grass signaling to? It may be letting insects know it needs some help.

After a lawnmower runs over grass and chops it down, the grass releases chemicals called green leaf volatiles in response to the injury. Green leaf volatiles, which are found in most leafy plants, act as a defense mechanism to keep pests away or make the plant less attractive to pests when it is damaged. These chemicals can protect the plant from fungi and bacteria growth and can act to prevent future damage by encouraging new growth.

There is another compound that is released by the plant during an assault called jasmonic acid. This compound is thought to deter plant-eating insects while signaling beneficial insects to come to the plant’s aid. Researchers at Texas A&M University found that parasitic wasps were attracted to green leaf volatiles and would lay eggs in the insects trying to eat the plant. This was a way for the plant to save itself from further damage.

But what actually gives grass that distinctive odor almost everyone is familiar with? One of the compounds that is released after grass is cut is called cis-3-hexenal. It’s also found in ripe tomatoes and other fruits and vegetables, and it can be isolated to be used in fragrances. But why does fresh cut grass smell so pleasant to so many people?

Australian researchers think they have found the answer and developed a spray called Serenascent that has the aroma of a fresh cut lawn or a walk through a forest. The researchers concluded that the smell of fresh-cut grass acts on the sympathetic nervous system, specifically the amygdala and the hippocampus areas of the brain, which are responsible for memory and emotions.

The smell of the fresh grass spray is said to regulate the release of stress hormones from the sympathetic nervous system. Students working on the project found that when animals were exposed to Serenascent, they didn’t incur damage to the hippocampus during stress. Researchers concluded that the aroma could lead to a reduction in stress, which could improve other health issues. The smell of fresh-cut grass might be good for your brain.

Sources: AgriLife Today, NCBI, BBC, The University of Queensland, Wikipedia, Live Science

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Daniel Ganninger - The writer, editor, and chief lackey of Knowledge Stew, the author of the Knowledge Stew line of trivia books, and editor of Fact World and the Knowledge Stew sister site on Medium, our ad-free subscription sites (you can find out how to join below). I hope you find things here to annoy those around you with your new found knowledge.

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