Lawn owner William Ray looks at the ecological benefits of not mowing and letting your grass grow longer.

We're heading towards summer, and the warmer weather that goes hand-in-hand with fortnightly lawn mowing for lots of New Zealanders.

But a number of ecologists are encouraging Kiwis to cut down on cutting the grass.

William Ray investigates how a 'no-mow' movement might be a win for people, plants, animals - and the climate.

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Associate Professor Bruce Burns thinks a lot about lawns. He's an ecologist at the University of Auckland, specialising in human modified environments.

His interest in lawns was first piqued on a holiday to Europe.

"If you go into those old cities the urban form is very condensed ... there's very little space between houses," says Bruce.

"It got me wondering: why do we have cities in New Zealand which are more spread out? I realised part of the answer was lawns."

Olivia Rooke-Devoy is a PhD student at Auckland University who's been researching lawns alongside Bruce Burns.

She said lawns are a relatively modern invention. They go back to 17th century England and France, where aristocrats had lawns cut by hand using scissors or scythes (the lawnmower wasn't invented until the 1820s).

" was a sign that you had enough money to own useless land," Olivia explains. " was a really exclusive endeavour which only opened up to the suburban class in the early 20th century."

Of course, today's lawns aren't just useless land; they're valued for sport and recreation.

But a lot of lawn is still just there for the sake of it, and some ecologists are encouraging people to think more critically about the environmental and financial costs of lawns.

The cost of lawns

Olivia surveyed a thousand Auckland households on lawnmowing and uncovered some truly astonishing numbers.

Her study found Aucklanders spend $131-million on lawn upkeep every year. And Bruce says local councils spend millions more on the upkeep of public parks, berms and walkways.

It's a big number, but Bruce points out that lawns account for 15 to 20 percent of most urban areas in New Zealand. In Auckland alone, that's 150 to 200 square kilometres.

Trimming all that lawn with petrol-powered mowers creates a lot of carbon. One study in Australia found that lawn mowing accounted for five percent of carbon dioxide emissions on a single summer weekend.

But even if you're using an electric mower, you're still contributing to air pollution…

Go to this episode on rnz.co.nz for more details