Are compostable plastic bags really compostable? Part 2

Part 2 of an experiment in home composting.

I am conducting an experiment to see whether The Guardian’s compostable bags do actually degrade in a home compost heap.

I finally got round to checking up on the heap on Sunday 7 July. This was exactly ten weeks after I had begun the experiment. Longer than I meant to leave it, I know, but various things intervened.

I began by removing all the material carefully with a spade and placing it into a bin. As I got near the bottom, I could see that there were two obviously separate large pieces of partly-decomposed plastic, but it wasn’t possible to tell which one was the Guardian bag and which was the one made by Greensax. There were also a number of smaller fragments which could have come from either bag.

I had to move them around a bit to get enough material exposed so that I could take a photograph, but this is roughly where they were when I uncovered them, and these are the biggest pieces I could find.

On checking back their positions in the dump from my earlier picture (left) I reckon that the fragment on the left is the Greensax bag and therefore the one on the right must be the Guardian. I was pleased to see that there were a lot of worms in the heap so they must have been doing a good job. There was no sign of the two wooden plant markers which I had carefully dated, which made me think that in the interests of science I should probably have used plastic markers. No matter.

I must admit that I was pleasantly surprised that so little is left of the two bags after just ten weeks. In my regular composting activities I have been using two or three Greensax bags every week for at least the last two years, and there are many fragments of plastic bag left over in all my bins. I have diligently moved these back to the large bags in which this autumn’s leaves will be kept, when the cycle begins again.

Having returned all the compost to the heap I then added two further distinct items, both of which claim to be compostable.

The first is a ‘compostable’ cup, acquired by my daughter at an event in the AirBNB offices. The second is the clear packaging from a loaf of bread, bought in a local food co-op. This is made by an Irish company, NJB. The company says that this is made from vegetable resources and is completely compostable.

I’ve covered all this with grass cuttings to a depth of an inch or two, then topped it off with more garden waste and vegetable peelings etc from the kitchen. I will carry on adding to this for another four or five weeks and then take a look at what has happened below the surface.


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