Saturday, December 31, 2011

Making compost in 18 days with Geoff Lawton

Building up layers of different materials

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.

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). 

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. 
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.
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.) 
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.
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.