Have you ever been strolling along beside a freshly mowed lawn, golf course or cricket pitch, soaking up that invigorating smell from the ground at your feet? The smell of freshly cut grass is one of life’s most unusual pleasures. In fact, it almost makes it worth mowing every week… almost.
So, what creates this smell?
It’s very rare to smell something when it’s cut; for example, we don’t smell anything when we cut on our nails or when trimming the branches of a tree. Grass, however, releases a very distinctive smell when it’s trimmed. This smell is caused by the release of enzymes, released into the world as ‘distress signals’, similar to how people sweat when they are stressed.
Plants have evolved many interesting ways to defend themselves, only some of which involve sending out distress signals. A few forms of external stimuli that are harmful to a plant’s well-being are dealt with in various interesting ways. The Mimosa pudica, popularly known as the ‘touch-me-not’, shrinks away when touched as a defensive mechanism against herbivores. Roses grow thorns, coconuts grow hard exterior shells, and Chinchona trees release a bitter substance known as quinine, which makes its bark very unattractive to eat, even for insects. Fortunately, quinine is one of the few cures for malaria. It just goes to show that everything has its uses.
Fresh-cut grass gets its distinctive smell due to a compound known as “cis-3-hexenal”. This aldehyde is what grass releases when you cut off part of the blade’s material. However, as with all things in nature, cis-3-hexenal turns up in myriad places. This is what gives strawberries the sweet smell that we know so well, and a similar compound is what gives the lush taste to apple juice. Similar compounds are also found in olives, spices, and types of alcohol. Some companies add it as an artificial flavoring in food products to give it a rich and earthy flavor.
Why Does Grass Do This?
We know that it’s a distress signal, but who is it meant for? Other patches of grass, to warn them of their impending doom? In fact, research indicates otherwise, suggesting that the signal was not actually for plants. One of the many other compounds released by grass when it’s mown is jasmonic acid, named as such because it was first discovered through jasmine plants. This substance acts as an insecticide, signaling plant-eating insects to stay away. The other function of this substance is as a distress signal to parasitic wasps to go and lay eggs in the plant-eating insects to keep them away. Therefore, substances like these have a dual function; to keep plant-eating insects away, and to attract parasitic wasps to destroy those insects. All’s fair in love and war – and nature, apparently.
The fresh-cut grass smell is unique in that it instills a sense of peace and harmony with nature; we feel a few moments of nostalgia, perhaps enhanced by the luscious petrichor of rain. What we don’t always realize is how plants perform a multitude of functions that are completely unbeknownst to us. It takes a bit of digging to find out that the smell is so closely linked to fruits that we love to eat, but at the end of the day, the smell is ultimately a survival mechanism that grass has evolved over millions of years to keep enemies at bay.