Ask Trash Queen: How do I hot compost my green waste at home?

Wednesday, 7 September 2022

Alex Kirkham is a waste specialist, answering trash-related questions in Sunday Magazine.

Q: Dear Trash Queen, I would like to have a go at hot composting my green waste as we produce too much for our council green bin. How do I go about doing this? – Sarah from Ōtautahi/Christchurch

A: Hot composting takes a bit of time and enthusiasm, but is very rewarding when you get it working. It’s all about getting the balance right between green nitrogen-rich material such as food scraps and fresh grass clippings with the brown carbon-rich materials such as dried leaves, straw and sticks, and just the right amount of water.

There are a lot of resources available on the internet and community gardens that run composting workshops most weekends up and down the country. Your local council is often a good place to link you to community groups that can help provide advice and troubleshoot.

If it’s excess garden waste you are producing, then you can build a one metre cubed pile in your garden which is a process a bit like making a cake. Layer up alternating layers of greens and browns. Each layer is around 10cm thick, with water added to each layer as you go.

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Then cover the pile with mats or black plastic to let it start its work. You need to turn or mix the pile every couple of weeks. Don’t let it dry out or it won’t stay hot.

You can visit sites like WasteBusters.co.nz for a recipe and super helpful tips and tricks.

If it’s only food scraps that you need to get rid of or you don’t like the idea of putting meat and bones into a larger compost heap for fear of pests, you can try hot composting using a Green Cone.

The average New Zealand household produces more than 200kg of unwanted food every year, rather than send that to landfill, it can be used to improve the soils in our gardens. Green Cones are completely enclosed, and use the heat from the sun to warm up the food scraps and rapidly break down the material much faster than an open hot compost.

They are a bit of an upfront investment, around $300, but easy to manage if you are busy and can’t get into the garden that often to tend to your open hot compost. Some councils are looking at them as an alternative to a kerbside food scraps collection where a property might be too remote to service, or for baches and rental accommodation where the food scraps volumes can fluctuate from one week to the next.

Send your questions of what to do with waste to sundaymagazine@stuff.co.nz