Encouraging air flow in the heap
Today I implemented something new with my active heap. Because I mulch most chunky things and am increasing the moisture content (the last couple of heaps dried out from heat) the lower middle of the heap tends to get a bit stinky. I add a fair amount of dry carbon (shredded paper and card) and it tends to go away after a turn, so it's probably to do with a lack of fresh air. We don't like anaerobic composition because it produces methane, is slow and smells really bad.
I'd been saving up some drain pipe offcuts – with 25mm holes drilled every 10cm or so – with the intention of placing them vertically, top to bottom, but on a whim had added one to the bottom of my resting pile when I turned it. Despite being a 3 month old heap the temperature has been constantly around 50-60°C and has shrunk dramatically over the last fortnight. There may be other factors (it was very dry so watering it brought it back to life) but I want to investigate the pipes some more.
I've always kept my heaps in contact with the soil, with no more than some mesh between the heap and the earth. This inoculates the heap with whatever bacteria is living in the soil and gives the worms and bugs easy access when it's time for them. So I wasn't keen to create an air gap at the base, as I've seen people do with a mesh-covered pallet or similar.
Roo, my compost buddy, had suggested putting a layer of woodchip at the base to aid aeration, and I liked this idea a lot. Woodchip in that density will not rot very quickly but will keep the continuity between compost and soil. So I added about 10cm from the allotment's communal woodchip pile (thanks local arborealists!).
The inspiration for putting the pipes on the base came from an industrial process of aerating massive windrows of compost using blowers. Here's a video of the basic idea. What I'm not doing here is attaching an electric blower, because there's no electricity on the allotment, but in theory I could have a solar powered fan which could be the next stage. I have ideas…
But the general notion is to encourage airflow up and through the heap. I cut the pipe offcuts to between 40 and 70 cm and drilled more 25mm holes in them. These pipes rest on the woodchip with one end butted up against the wire mesh so they're open to the air.
I then dumped about 80cm of rotting material back on top of the pipes and added this week's new stuff as usual. The test will be when I pull the thermometer out in a couple of weeks and smell the tip. Will it stink?