How long does it take for 'compostable' packaging to actually break down?

A swathe of compostable products have swept the market, sold with the lure of helping save the environment. But just how compostable are they really?

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With a little help from Auckland’s Bayview School, we put the composting times of a coffee cup, bottle and biodegradable bag to the test. Source: Seven Sharp

There's a secret to getting compostable products to break down properly, and it's unlikely just chucking it on the heap in your backyard will do the trick.

Seven Sharp put it to the test with a bottle, a coffee cup and a biodegradable bag - with the help of Bayview School, on Auckland's North Shore.

The same three items were also composted at Organic Market Gardens in Auckland CBD, which has a managed compost.

Nick Morrison is the fountain of all composting knowledge and he shared some tips for his Composting 101.

  • Make sure you rip up or cut up what's going into the compost, making it as small as possible
  • Make sure your compost has got enough dry brown stuff - things like brown paper bags and egg cartons
  • If you can't compost at home, find someone who can.
  • If you look online, places like Kelmarna Gardens in Herne Bay collect compostable material from the neighbourhood - and they're not the only ones. Nearby composts are shown on

After three weeks, the ones at Organic Market Gardens had all but disappeared, but it's not easy. The compost gets incredibly hot, reaching 60C - hot enough to burn your hand.

Meanwhile at Bayview School, things look a bit different. In the bottle and bag they're starting to see changes, but it's nowhere near the dramatic progress of the hotter compost.

"We want to see an urban network of hot composting," Mr Morrison says.

"We want to see those set up all around cities in New Zealand, where the unwanted food is processed into soil."

Hot being the operative word if you want to break down that waste and turn it into something sweeter