The compost heap's gone critical. .

The compost heap's gone critical. ., originally uploaded by mike1727.

The compost heap is cooking away nicely- in fact it's steaming.

A quick probe registered temperatures around 62C in the centre of the pile- that's 143F, which is plenty hot enough to kill weed seeds and other nasties, and indicates that the carbon:nitrogen balance is about right.

Cornell university has a page on composting physics which describes the temperature characteristics of decomposition.

Material choice is key- the last load (which was around a 30cm layer over 1sq m so about 0.33 cubic metres) consisted of:

• 2 grass boxes grass clippings (form a recently-fed lawn so probably high in N)
  1 shredder box (40cm*15cm=0.045 cubic metres) of shredded paper (bills, very satisfying)
• approx 4 kg spent coffee grounds
• approx 3kg kitchen waste (veg peelings, coffee grounds, teabags and paper kitchen towels)
• 1 large cup Garotta compost accelerator.

No leaves this time, unlike previous loads.

This was mixed together, on top of (but not mixed with) an already-composing layer of much the same material. No added water this time since the grass clippings were fairly moist.