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| Building up layers of different materials |
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| cold composting bins |
We
cold compost, which is to say that we add material to our
compost piles as it arrives from kitchen or vegetable plot and it moulders
away, decomposing slowly. We
alternately use four adjacent boxes and when the compost is about ready, we
empty that box and riddle it to remove uncomposted material, which goes back
into a fresher pile. It takes
months to make compost this way but is relatively low maintenance.
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| if you just add water at the end, it won't soak through evenly |
The alternative is
hot composting, which involves creating a large pile all at once (which heats up) and then turning it regularly to
maintain the heat. We've tried
it before but were inspired to have another go after watching the very specific
advice from permaculture hero Geoff Lawton, on his new video,
Permaculture Soils
His informing belief is that “it’s not the soil itself, it’s
the soil life that is the most important element.” He teaches us to inoculate the soil with bacteria by using a
very diverse mixture of compostable materials such as different manures (the
nitrogen component) dried grass toppings, green grass clippings (providing the
‘yeasts’) along with shredded and partially rotted wood (food for fungi).
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| six days in |
He talks about adding activators, such as urine, comfrey,
nettles, yarrow, fish or animal remains to kick start the decomposition
process. He also mentions adding
charcoal for its surface area (I’ll blog about what I’ve recently learnt of
biochar soon). The whole lot should be wetted (see below). One needs enough material to create a
minimum of one cubic metre in total, otherwise it won’t get up to the necessary
temperature.
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| Cat enjoying the warmth generated by the compost process |
We gathered pig manure, chicken droppings, rabbit pellets
and sheep poo. We added wheat
straw and fresh grass clippings, chipped wood and comfrey leaves and litres of
wee collected from our urine-separating compost toilet.
He talks of having 25 parts nitrogen to 1 part carbon but,
as I wrote in my recent article for
PermacultureMagazine on our compost toilet: “
The ideal carbon/nitrogen ratio of
30 : 1 is often quoted but rarely explained. It certainly doesn’t mean 30 times as much straw as solids;
in fact, both faeces and urine contain carbon and nitrogen in their chemical
makeup… Don’t bother getting the
scales and tape measure out as you search for the correct amount.” It’s a learning process and you’ll find
that too much nitrogen means that the pile gets too hot and reduces in volume,
losing goodness to oxidation. Too
little and your pile won’t get warm enough to kill weed seeds and break down
the woody material.
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| 8 days and the colour is beginning to change |
There are two criteria to measure, that’s the moisture
content and the temperature. For
the first, grab a handful and squeeze: it should just drip. For the temperature, he tells us to
shove our hand in. TAKE CARE, as
it can get really hot. Be sensible
and open up the pile a bit and get a feel before you actually touch it. At 60ºC, you wouldn’t be able to leave
your hand there. We actually used
a meat thermometer and pushed the whole thing in, probe, dial and all, leaving
it for a few minutes before retrieving it and looking at the temperature. We tried it in several positions in the
pile. Aim for a min of 50ºC max
70ºC, ideally between 55 and 65. (Above
70ºC is beyond the limit of life for our decomposing bacteria and the process
becomes anaerobic.)
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| 10 days |
Construct your pile, cover it up with old tarps or plastic
sheeting (leaving an air gap at the bottom) and leave for four days. Then unwrap and turn the pile. We used a pitchfork and rebuilt the
pile alongside itself, trying to put the stuff that was on the outside on the
inside and vice-versa (if you see what I mean!) Wrap the rebuilt pile up again and, from then on, the pile
gets turned every two days for the next fortnight, reaching its maximum
temperature on the second or third turn, i.e., 6 or 8 days into the process,
when it should attain the ideal of around 60ºC. Geoff’s claim is that, if you get it right, it gets hot
enough and decomposes without losing volume.
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| 16 days and the heat has reduced but we're seeing fungal growth |
The photo sequence shows our experiences with our first two
batches. We now think that the
moisture content is vital and ended up adding a lot at the start to pass the
squeeze test and a bit during the turning process. We think we had proportionally too little nitrogen on the
first batch, maintaining volume but not being fully composted at the end and
never quite getting up to the desired temperature. We overdid the nitrogen in the second version, getting good
decomposition but losing a lot of volume.
This last photo shows our second attempt, at the end of the process.
It's much darker, has decomposed more than the first but we've lost
volume.
We can generate or get access to the necessary amount of
material to build a cubic metre pile and it’s very useful to create such a
quantity of compost in just 18 days or so, so we will keep trying.
