Biodegradable, degradeable, compostable… these terms are often used interchangeably but they actually mean slightly different things.
Jo McCarroll issues a plastic-free garden challenge.
Degradable simply means something will eventually break down – but almost every substance will break down if you wait long enough. Even plastic will degrade under the right conditions and over enough time, although it can leach potentially toxic chemicals as it does so and also is prone to breaking into what is just millions of smaller pieces of plastic (often called micro-plastics) which end up in the oceans and build up in the soil.
Biodegradable means something will degrade due to the actions of naturally occurring microorganisms – bacteria and fungi. But something can still be called biodegradable even if it will take a long time to break down and possibly leave potentially harmful residues behind.
Compostable means a product is biodegradable and breaks down into the non-toxic components of water, carbon dioxide and biomass. But products that are labelled as compostable have usually been tested under commercial composting conditions where the temperature, moisture level and available oxygen can be tightly controlled. Home composting is obviously on a much smaller scale, so is unlikely to generate as much heat. Some products labelled compostable might not break down in a home system. Finally a few products or packaging are classed as “home compostable” which – as implies – mean they break down in your compost bin.
These words are being used a lot around plastic, especially plastic packaging.
Probably because of an increasing consumer concern, there’s been a huge increase in single use plastic items labelled as biodegradable or compostable. And at first that sounds like a good thing. But when ”biodegradable” doesn’t necessarily mean environmentally benign and ”compostable” doesn‘t always mean compostable at home, it’s not quite so straightforward. Plus New Zealand does not yet have a standard that plastic needs to meet in order to be labelled as biodegradable or compostable (a working group is currently looking into whether we need one and certain manufacturers voluntarily meet some of the existing international standards). A report by the Parliamentary Commissioner for the Environment in July, Biodegradable and Compostable Plastics in the Environment, suggests the array of environmental claims being made about some plastic packaging ”might easily lead to misunderstandings” and some of these new eco-plastic options ”amount to little more than greenwash”.
What does all that have to do with gardening, you may ask?
Well, I think that gardeners consider gardening to be an environmentally friendly thing to do. But I also think some gardeners might be unaware of how much plastic is used in their garden, and often only used once – I was, when I stopped to think about it. Seed-raising mix and fertiliser in plastic bags, garden sprays in plastic bottles, plastic plant pots and labels. Some can be recycled, true, but as is increasingly clear that’s not quite the complete solution we once hoped. Paul Evans, chief executive of Waste Management Institute New Zealand, commenting on the Parliamentary Commissioner’s report, puts it like this. ”No single-use option is a good choice.”
Is it possible then to have a plasticfree garden?
There’s certainly a groundswell of interest in trying to. Earlier this year British gardening celeb Monty Don called for gardeners to reduce their use of plastic and pledged to cut back the amount used on the TV show Gardener’s World, which he hosts, and in his own garden. A nursery and garden centre in the UK has vowed to go plastic free in 2019, the first one in the world to do so. At my place I’ve switched to wooden popsicle stick plant labels (although I’m also still re-using the plastic ones I already had). I made my own seedling pots out of newspaper this year. I don’t have to ditch plastic weed mat since I’ve never been a fan (just mulch, mulch and mulch again). But I haven’t managed to avoid plastic completely – every impulse plant buy is likely to bring in another plastic pot! So if you‘ve successfully reduced or eliminated plastic from your garden, send me your practical tips. I’ll give them a go at my place… and publish any particularly clever suggestions in a future issue.