Hot compost takes off

On Friday 30th November, Richard Wallis from NZ Box, came to talk about composting and introduce his compost box design. Richard led an inspiring, dynamic group discussion on soil health and regenerative practices, followed by a demonstration constructing and filling the NZ Box composting unit on Saturday afternoon with a variety of interested community members.

The Box was sited on Pukepoto Rd, a site organised by Pam and Doug Clarke of The Good Life Project.

Firstly, Pam took us around their facility, just below the Box site, that she and husband Doug have built to engage and educate the intellectually challenged members of our community. 

Working together with their aid workers, individuals and school groups tend their own garden patches and learn to grow their own food. 

It was inspiring to hear about the work and to see the glorious gardens flourishing with healthy produce.

After the tour, Richard Wallis arrived with the parts of the frame and we began construction of the NZ Box composting box. 

He showed us how the Aluminium framing bolts together to ensure a strong, sturdy structure which will withstand the elements. 

We lined the base with fine wire mesh and screwed it in place to rodent proof the box. The wooden slats which form the sides of the box slip into place one on top of the other. For ease of building the compost pile, we built the sides up as we filled the box. 

These easily removable planks which create the sides makes for easy turning of compost from one bin to another if you setup a row of boxes. The NZ Box is designed so that a series of boxes can all be connected together and the planks between the boxes removed easily for turning the compost. It also comes with a lid to make sure your compost doesn’t get too wet in the rain and too hot in the sun. 

What went in to the compost box?

Firstly, we lined the base of the box with a thick layer of carbon rich material. Sawdust, fine wood chip and dried leaf mulch. This helps to absorb any excess moisture that may seep out the bottom of the box. 

On top the carbon rich base, we added alternating layers of nitrogen rich material and carbon rich material.

Some of the carbon layers included; Shredded coconut husks, newspaper, compostable paper cups, more sawdust and wood chip, and delicious smelling coffee husks.

Some of the nitrogen rich layers included; Kitchen scraps, horse manure, and a pile of corn husks. 

We decided to leave out the oyster shells and add them later after they had been crushed. They add essential minerals such as calcium which is often a limiting factor in plant nutrient absorption. 

The NZ Box aluminium frame can be custom cut so you can build the box size you want. 

To make a hot compost the pile has to be big enough to insulate itself. 1.2m cubed is a good size for a hot compost. Turning the compost helps to aerate it thereby encouraging the populations of aerobic bacteria that produce heat in the pile. 

The heat destroys pathogenic bacteria, viruses and parasites, but if it gets too hot it destabilises  beneficial carbon stores that create healthy, well structured soil. 

Nitrogen heats the pile up whereas carbon cools the pile down. This means the correct ratio of carbon to nitrogen is essential to create the best compost. A ratio of 30:1 carbon to nitrogen is a well known rough standard. Of course, all of the ingredients have their own ratios of carbon and nitrogen, so how can we measure what to put into our compost pile?

Richard Wallis suggests experimenting by starting off with roughly half-half carbon rich materials to nitrogen rich materials, and over time increasing the ratio of carbon rich materials until the composting process stops. At that point you have discovered how much carbon is too much. 

The most important thing to know about composting is that its easy to do. Just make sure you add some things from the carbon list and some from the nitrogen list. Turn it roughly once a week and water it so it doesn’t dry out. It should be only as moist as a damp sponge. 

For any more tips on composting come down to the EcoCentre on Bank Street and talk to our volunteers and staff between 10am and 4pm, or bring your questions to Te Hiku Hauora Maara Kai on a Tuesday or Thursday 9am to 12pm and spend some time learning hands on in our garden.

by Jo Picollo

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