The Self Preservation of Grass

By Brigid Gallagher 04/11/2011


The sun is hot outside, the cicadas are buzzing, the next door neighbour is mowing their lawn, the beginning of summer is here….

             You step outside your house into the noise and heat of the day, and….

Mmmm…. that lovely smell of newly cut grass.

Its fresh, green and very inviting.

But the same cannot be said for the small, generally unseen members of our gardens. While we might love the smell of fresh cut grass;  insects and other ground bugs don’t have the same reaction. 

This week Gerald Smith, Associate Professor at Victoria Universities Chemistry Department and Heritage Materials Science programme presented a paper to members of the New Zealand Conservators of Cultural Materials conference at the Carter Observatory in Wellington.

Smith and a team of chemists and heritage professionals, including weaving and fibre expert Rangi Te Kanawa, have been looking at the effect of acetic acid on Maori textile fibre. Known as the vinegar effect, they have been testing the production of acetic acid during the degradation of fibres used by Maori, namely Phormium tenax (harakeke or New Zealand flax).

The physical effects of degradation of these fibres include colour change, embrittlement and in extreme cases, loss.

But they have found through accelerated aging tests that not only is acetic acid produced but also furfural (an aromatic aldehyde derived from a variety of agricultural byproducts) and Coumarin (a fragrant chemical compound in the benzopyrone class). 

Coumarin is what we smell and enjoy when we take a deep breath taking in the aroma of freshly cut grass (it is also commonly added to pipe tobacco and some alcoholic drinks to lure us into partaking)

Coumarin is also what insects smell and then run for cover (I am not sure if that should be taken literally!).

Coumarin is volatile, plus a natural anti fungal and pesticide.  Bugs are repelled by it…but what appealed to me in Smiths presentation… was how in the production of these anti-bug properties, grass is giving itself a chance to heal without the being compromised to the chomping jaws of our garden dwellers.  It is an act of self preservation and…natural conservation.

But what about historic and prehistoric Maori fibre textiles…

Like acetic acid, coumarin is photosensitive (essentially this makes colours fade) and its evolution of hydrogen peroxide also causes more damage (just think of your friends bleached hair and how dry and brittle it gets with repeated application!) to these beautiful examples of Maori taonga (treasures).

Limiting the presence of such chemicals as acetic acid and coumarin can help to preserve beautiful fibre textiles such as kete, cloaks and the like, in private and public collections.

So what to do…even if you cannot smell vinegar or freshly mown grass next time you open a draw with some beloved fibre textiles, in a museum or in your own home…Smith says

…lower the moisture in the air and the temperature if you can, but most of all, get the air moving and flush away those chemicals! 

And next time you walk over that freshly mown grass, take a moment to stop and think.  You are witnessing a wonderful moment in the regeneration of our natural environment.  Grass sending out its signal that it needs time to heal.  And I reckon that is very cool!