More and more retailers are swapping plastic bags for compostable ones - but is it actually better for the environment?
The Warehouse Group last week announced it would stop using plastic bags and introduce compostable ones by the end of the year.
The Warehouse said the compostable plastic bags decomposed within 12 weeks in compost and were non-toxic.
A Warehouse spokesperson said they wanted to be proactive and get rid of plastic bags, and it was still working on advice for customers about how they could dispose of them correctly.
Consumers wanting to ensure their compostable plastics don't end up in landfill could sign up to an organic waste collection service, but at a cost.
However, switching bags was only part of the challenge because there was not enough facilities to compost them, Sustainability Trust spokesperson Nada Piatek said.
"The catch is that there isn't a clear pathway for these bags to get to the compost facility, and in fact there are only 11 compost facilities in New Zealand that are set up to take these products," she said.
"Unless they are recaptured and taken to a composting service purposefully - if they just end up in the landfill or even in compost they are indistinguishable from a plastic bag and therefore the compost service will just take them out.
"It actually makes more work for the compost service and there's no benefit."
Ms Piatek said retailers should provide access to composting services.
Meanwhile, Countdown's first 10 supermarkets went plastic-bag free on 21 May, with the remaining 172 stores to follow by the end of the year.
Once in landfill, compostable plant-based bags break down just like regular plastic bags, release methane into the atmosphere and contribute to global warming.
Founder of Beyond The Bin, a waste management company, Kim Renshaw said decompostable packaging can actually be confusing for consumers who may think it will break down in their household compost.
Ms Renshaw said she did not think the bags could be composted at home on any large scale.
"If you put one thing in there and give it a good turn, it's going to be fine but if you start putting heaps of these products in there it's certainly not going to break down very easily, and it's probably not really add a lot of value to your garden, either."
Ms Renshaw said to break down compostable plastics in the backyard, they often needed to be shredded and treated with artifical compost accelerators.
And not every industrial compost facility could process the decompostable bags.
"Just because a composting facility says that they can process a type of material doesn't mean there is a service provider in place to take this material to the facility," she said.
"It also doesn't mean they can take loads of large volumes of this product either."
'Lack of standards'
Ms Renshaw said New Zealand's lack of standards for packaging manufacturers creates problems for composters.
"We've got all this compostable plastic in the marketplace that isn't regulated against any standard," she said.
If composting facilities were being asked to process this packaging it had to be regulated to make the work possible, she said.
Envirofert is an industrial composter in Tuakau, which collects green waste and compostable packaging from the Auckland, Waikato and Bay of Plenty regions.
Site manager Paul Yearbury said poor labelling and the lack of a national standard, made it hard to know what products could be broken down.
"There is biodegradable films and then there is true compostable packaging, generally cornstarch based.
"We have a 22-week composting cycle, and anything 'biodegradable' doesn't fit into our timeline," he said.
Non-compostable products which end up at Envirofert are expensive and tedious to deal with, he said.
"From our point of view, it's for people to prove to us that these products are not going to harm our compost because that's what we've got to protect at the end of the day," said Mr Yearbury.