Can compostable plastic break down in a home compost system?

The soaring consumer anxiety regarding the downstream effects of plastics has resulted in a huge increase in single-use plastic packaging and items labelled as 'compostable plastic ‘biodegradable’ or ‘home compostable’.

But what do these labels represent when discarding these items in your home compost? The fact is it has yet to be discovered how those items will react in a range of composting environments - or how many Kiwis compost at home, or what the norms in a 'usual' compost system in New Zeeland may be.

So research is being going on to discover how home compostable packaging breaks down into a range of distinctive composting systems nationwide.

As per the norms, to be labelled as biodegradable plastic, the item must break down via the actions of living organisms like fungi and bacteria, which are active under specific conditions. But, if biodegradable plastic decomposes under other conditions - such as in the sea or landfill - it can divide into those highly problematic microplastics.

To be tagged as compostable, plastic must be designed to break down in commercial compost, but it may not decompose in your home system (which is not likely to reach the same temperatures).

Then there are a few plastics that are tagged as home compostable and which are crafted to break down in a so-called typical compost bin. But what is the range of conditions in composting bins in New Zeeland? It is not known. So it is impossible to say if 'home compostable' packaging will break down in all of them.

Also, what if one doesn't have a compost bin and the products end up in a landfill? Well, composting microbes need oxygen, and for the most part, waste in landfill decompose anaerobically without oxygen. That indicates compostable plastic will either break down and release methane or stay inert so the biomass within isn't emitted.

Home compostable and compostable plastics also can't be recycled and cause problems if mixed with plastics meant for recycling because they can render them unrecyclable.

Waste minimisation funding has been received to examine home and commercial compostable packaging. Tests will be performed in the lab and a few compost bins to observe how well different plastics and packaging disintegrate.

This implies that by 2030, wherever Victorians visit or live, they'll have a constant roadside bin system.

But because of the high cost of detailed testing, it will be possible to test only a minimal range of home composting environments within a restricted range of ambient temperatures. And, as gardeners already know, products in compost break down differently depending on many factors, particularly the temperature (as in the weather and the internal temperature of the heap).