Economic and ethical incentives increasingly steer compost and green waste away from landfill. However, composting is more complicated than simply chucking grass clippings in a box in the backyard. One common herbicide, clopyralid, can make compost dangerous for numerous plants, so WasteMINZ looks at ways to get it right
You may have heard the phrase ‘circular economy’, but what does it mean and how does it apply to landscapers? A circular economy is, in simple terms, when materials are reused or recycled rather than being disposed of in landfill, allowing the value of those resources to be maintained for as long as possible. When it comes to the resources landscapers use, green waste is an obvious and valuable material that is highly beneficial when kept out of landfill, and ideally reused as compost. If compost is made and used properly, it can also be a valuable soil enhancer that reduces the need for chemical fertilisers and water.
Diverting green waste to composting reduces the generation of methane, which is generated when organic waste is disposed of in landfill. Increasing the amount of green waste diverted is an important part of New Zealand’s strategy to reduce its carbon emissions. To ensure the loop is closed, there need to be economically sustainable markets for the end product – there is no point producing compost if there is nowhere for it to go.
Landscapers play an important part in the compost cycle. Landscapers can provide the raw materials for compost by ensuring green waste from lawns and plants gets taken to a composting facility. They can also ensure the product is viable by buying back the finished compost to improve soil quality for their clients. However, care needs to be taken to ensure the compost produced is not harmful to plants.
Clopyralid is a common herbicide used to control broadleaf weeds, such as thistles, dandelions and clovers. It does a great job at what it’s designed for, but has repercussions when it gets into commercial compost. While some plants are tolerant to clopyralid, crops such as peas, tomatoes and potatoes aren’t and plants can be ruined.
Clopyralid makes its way into compost when grass clippings or other green waste sprayed with the herbicide are composted. Because clopyralid doesn’t break down during composting, while other materials do, the concentration of clopyralid actually increases during the process.
Herbicides containing clopyralid are only available to registered users, including many commercial landscapers. Landscapers can help ensure it doesn’t get into compost by avoiding using it where possible. For example, helping clients design a garden with minimal or no traditional lawns and more groundcover lawn (only if they’re open to it, of course!).
For landscapers responsible for large expanses of lawn (or golf clubs, sports grounds or schools) who cannot avoid the use of herbicides containing clopyralid, setting up
an onsite composting system to process the green waste exposed to it is another solution. As long as this compost is not being used on the plants vulnerable to it, then it should cause no issues when applied to gardens.
If you need to take lawn clippings that may contain residual clopyralid off site, it is likely that they will need to be disposed of to landfill to avoid contaminating compost. Check with staff when you drop the materials off.
Setting up an onsite composting system
Getting the perfect compost is not a matter of throwing it all in and seeing what happens. For those with a scientific bent, ensuring the compost system is operating at its optimum conditions can become a bit addictive! A quick web search will yield multiple guides for setting up your own composting system.
Landscapers will be easily able to construct a two-bin compost system (two bins are needed so one can rest while the other is still being added to). There are many great online tutorials for how to build such a system.
The best compost has a ratio of 25:1 of carbon (“brown” material such as leaves, straw, paper, old dead trees, saw dust, pine needles etc) to nitrogen (“green” material such as lawn clippings, freshly clipped plant matter, limited food waste – ie, no meat, dairy or cooked products). The moisture content should be about 50-60%, oxygen content about 12-14% and pH levels 6.5-8. The other important factor is temperature, which should be maintained at 45-65°C. You will know your compost is ready to use when it smells earthy and looks like soil.
We often work in our own little silos and fail to see the bigger picture. But, as this article demonstrates, we are all part of a bigger picture and an essential part of Aotearoa’s important transition to a circular economy. With help from everyone, we can improve our soil and reduce carbon emissions.
Sarah Pritchett is Sector Projects Manager for WasteMINZ, and coordinates the Organic Materials Sector Group. WasteMINZ is the largest representative body of the waste, resource recovery and contaminated land management sectors in New Zealand with over 1,500 members – from small operators through to councils and large companies.
For more information on responsible composting, contact Sarah at firstname.lastname@example.org