Kiwi Polemicist

December 4, 2008

Waste glass has been used as a mulch in New Zealand vineyards

Stuff is reporting a successful trial of crushed waste glass as a mulch under grapevines. It retains warmth and moisture in the soil, suppresses weeds, and reflects light to aid the ripening of the grapes. The glass is the size of coffee grains, safe to touch and has improved yields.

I have some horticultural experience and glass mulches sound great to me. Organic mulches like bark and straw break down after a while and require replacing. Plastic sheeting is expensive, fragile, and has to be manufactured from scratch, whilst also preventing water and fertiliser getting to the soil. Ground glass is durable and lets water through, whilst also adding sun to the parts of the fruit that don’t normally get much light. Perhaps the only downside would be a dazzling effect for the workers.

There is a huge amount of waste glass around and this is an excellent use for it. This also shows how environmental “problems” can be solved by the capitalist free market without adding to our excessive burden of regulations.

I’d be interested to hear what Samuel Dennis, a soil boffin, thinks about glass as mulch.



  1. It sounds a good idea to me too, glass is completely non-toxic and there’s tonnes of it going into recycling bins every day needing a good use. However I do have a mate who works for Extenday selling cloth sheeting (ie porous sheeting that will let rainwater through) to do the same job, and I understand that this reflects the vital wavelengths of light more effectively than crushed glass does. It is however more expensive than glass. So there are a few options that a horticulturist would need to weigh up.

    Most environmental problems can be solved without regulation, and this is a great example.

    Comment by Mr Dennis — December 4, 2008 @ 3:20 pm

  2. Samuel: I’ve had a look at the Extenday system and it looks very complicated, with ropes and clips all over the place holding the sheets down. You’d also have to remove it before harvesting. Thus the labour and maintenance costs are high.

    When I worked on a kiwifruit orchard I had to go along the rows and clear the irrigation nozzles under the vines (great on a hot day because you got soaked). This would have been a nightmare with Extenday system due to the ropes everywhere waiting to trip you up.

    Crushed glass is simply poured into place and can be walked on. Maintenance would be minimal, just a top up every few years I expect.

    How would the soil be affected if it absorbed large amounts of glass over time? Would it simply become more like a sandy soil? That would be good if you wanted better drainage.

    Comment by kiwipolemicist — December 4, 2008 @ 3:48 pm

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