Worms working hard in new vermicomposter

Student journalist Alex Zhang chats to Matt Cummings about soil health and our new worm friends at Te Hōnonga a Iwi

Our new vermicomposter unit, the Food Phoenix, is hard at work in the mara kai, turning organic waste such as food scraps, green waste, and even shredded office paper into compost.

Funded by the Sky City Foundation and built by Untangled Landscapes, it’s a game-changer for our restoration project, encouraging circularity and sustainable restoration.

Vermicomposting is a natural process where worms and microbes work together to turn organic waste into high-quality compost.

“Vermicomposting is an excellent way to handle waste streams which come frequently, a little at a time. The bioreactors that the restoration operates are at the other end of the spectrum; taking large amounts as a batch but then being left alone for 12 months,” says Matt Cummings from Untangled.

By using the two composting methods together, Te Hōnonga a Iwi will be able to accept a much greater range of organic matter and recycle it efficiently, storing the carbon present in that waste and building soil for our native plantings and food gardens rather than allowing it to escape back to the atmosphere.

The Food Phoenix has been designed to be just the right size, slotting into the gap between large industrial windrow methods and small backyard systems, Matt says.

At 800 litres, with a one-square-metre surface area, it allows a wide range of organic food to be fed to the worms inside, producing high-quality vermicast.

Because of its size, even foods worms don’t favour — like citrus, onion or spicy scraps — make up only a small part of the overall feed.

This allows the system to handle a broader mix of inputs, including items often discouraged in smaller home bins, as long as they’re added in moderation.

And it’s not just about the worms, Matt says. The unit hosts a whole world of microbes.

“If the worms themselves don't eat something, you can bet there's another saprophyte in the mix of a healthy worm farm's microbiome that will love it.”

Another challenge with smaller worm farms is that it’s harder to build up a good volume of finished compost without disturbing the system, Matt says. As a result, they often produce more liquid “worm tea” — or leachate — which is sometimes promoted as a key feature.

While this liquid can be used as a fertiliser, it’s not as beneficial as solid worm castings. It contains only soluble nutrients, whereas castings also help improve soil structure and support healthy soil life.

In fact, relying too heavily on liquid fertiliser can have downsides. It doesn’t contribute to building soil health in the same way and, over time, plants can become dependent on it.

Leachate can also be a sign that a worm farm is too wet. Ideally, the system should be moist — damp enough that a handful of compost will drip if squeezed, but not so wet that liquid is constantly draining out. These conditions support a healthy, oxygen-rich environment where beneficial microbes and fungi can thrive.

Fungi are especially vital because they are the only organisms that create really stable molecules such as glomalin and humus, binding up much of the carbon that bacteria would quickly respire away if left unchecked.

The Food Phoenix is designed to provide enough space and balance for this process to happen properly, producing high-quality castings before the system needs to be emptied.

Te Hōnonga a Iwi project co-ordinator Nicky Shave says one of the most exciting aspects of the project is that it will allow local businesses to bring their organic waste to the restoration, taking it out of local waste streams. 

The Food Phoenix is also pest-proof, enabling us to harvest organic waste that might attract pests otherwise and convert it to high-grade compost without endangering wildlife in our ngāhere that we are working hard to protect and regenerate.

When the vermicomposter is full and all the biomass has been processed to vermicast by the worms, the restoration team will empty it, lay a new organic food bed for the worms and place them back in it again to continue their special work.

Matt Cummings expects each harvest to contain around 0.75 cubic metres of finished castings (valued at $1,500-$2,300 per cubic metre), 100 litres of charged biochar (valued at $8 per litre) and 50 to 70kg of worms (valued at $100-$140 per kg).

With this precious vermicast, Te Hōnonga a Iwi’s vision is to improve soil health, which in turn improves freshwater quality by preventing erosion in storm events, and restore the wellbeing of our local ecosystems that will enable nature to thrive once again.