Composting with Biochar

Compost has to be one of my favourite topics after Biochar, I used to help my father make compost by the ton and boy did it stink, not quite enough carbon and oxygen for my liking, we didn’t have access to enough carbon sources way back then, but now I’m the other way around here, nitrogen is often limited due to dry weather apart from our wet grass growing summer, but you learn to cope and find replacements. I use 4x 400lt black recycled plastic compost bins and a 1500lt wire cage design here, they are open on the bottom and full of earth worms when they are ready to use. I would recommend using at least two compost bins as compost often needs to sit for a couple of months after filling and this allows a second batch to be well under way when you empty and use the first bin.

While the perfect compost process can take years of experience to get right, a quality compost should produce a earthy smelling humus with few lumps of recognisable organic matter, adding chunky Biochar will add hard lumps to your humus compost as Biochar will not break down of rot in even the hottest compost bins, but that’s ok.

A good compost is all about getting the ratio of carbon and nitrogen right, with a sprinkle of oxygen, moisture and activators thrown in. What’s all this carbon and nitrogen ratio talk about, think about Carbon as any dry brown organic matter or woody material, think of nitrogen as anything fresh or green, I class animal manures as nitrogen, same goes for all kitchen waste and the odd road kill or dead rat. If you only use carbon sources in your compost the process of breaking down will take much much longer or might not even happen, if you only use nitrogen sources like fresh grass clippings or kitchen waste you will tend to get a smelly wet pile of yuck to deal with.

Layering Compost is the secret, layers of carbon and nitrogen made in a single batch or as you go composts, how much of each? that depends on what you have access too, as a general rule add 15 parts carbon to one part nitrogen, but it’s sometimes hard to know how much you have added, what I have done here to make composting easier is have a pile of carbon sitting next to your compost bin so each time you add your daily nitrogen kitchen waste you can cover it with carbon matter, while fresh grass clipping are classed as nitrogen if you let them dry out they become a source of brown carbon which is easy to keep next to you compost bin. When you start a batch of compost the first layer should be coarse carbon or a 15cm layer of sticks which create an air vent at the bottom of your compost helping the composting process and reduce the wet anaerobic (without air) issue some compost makers get including myself.

I tend to either make a full batch of compost which does take a little planning like pruning in the morning and composting in the afternoon, or make at least half a bin which is then slowly filled up from kitchen green waste and my pile of carbon matter. Try and keep your carbon layers no more than 5cm thick (2 inches) and keep the nitrogen quite thin, after a couple of layers I like to add one of my many compost activators, these are designed to fire off the tiny organic life in your compost bin which do most of the breaking down, What I use here is, worm wee (vermiliquid), old compost teas, human wee, molasses, honey, some of your last compost and the odd bucket of dead smelly rotting cane toads.  I also add rock dust or minerals over layers as I go, a cup full of rock dust or dolomite every 5 layers or so would be about right.

So what about Biochar?? I don’t tend to class Biochar as a carbon source when I’m making compost, why I hear you ask? Biochar will not break down like woody carbon in your compost, it will just fill up like a sponge with moist humus, tiny organic life and minerals, so my thinking is to try and get your Biochar spread as evenly as possible  through all of your compost bin, so each time you add a nitrogen layer I add a hand full of Biochar across the whole layer, I have tried adding dense layers of Biochar in past composts and found the larger earthworms had moved through those layers to get higher in the bin but parts of the Biochar layer didn’t get exposed to humus and stayed dry. The other benefit of evenly spreading Biochar into your compost is you will not have to mix it up with a garden fork when it’s ready to use.  How much Biochar to add? I wouldn’t add any more than 10-15% Biochar that’s 40-60lt in one of my 400lt bins. If you have access to heaps of Biochar I would think about liquid composting which I will cover in my next post.

When spreading compost either cover it with a thick layer of chunky mulch like sugar cane, hay or lucerne. Digging it in is optional but sunlight will damage humus rich compost creating a hard surface crust, so if you don’t use mulch dig it in.

Just a quick note on things not to add to you compost, plastics, treated green or blue tinted timber, fruit fly infested fruit, fungus infected clippings, any thing that will not break down or has been exposed to chemicals, don’t add meat eating animal manure if you are going to use the compost for food crops as it can contain some nasty bugs. Some people don’t add bones to composts due to rat issues but I do and I have never had any problems here, large beef bones don’t tend to break down so I turn them into Biochar.

Final note, please take care when handling compost, it’s packed with millions and millions of tiny bugs and fungus spores, use a mask and gloves, dampen down the compost if it’s a little dusty or dried out. If you have a chest cold leave it alone as your lungs are already getting bashed about and they don’t need to be exposed to compost bugs, also avoid any open cuts or wounds as I often end up covered in compost after moving it to my wheel barrow then spreading it around my garden.

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