Kay wrote:

I presume it is to do with the proportion of relatively harder and
softer stuff in the heap. Even tree leaves will decompose in a
'normal' heap, but they are slower than other things, so it's better,
with autumn quantities, to compost separately. And you need more of
the softer stuff to generate the heat for the hot process, so your
leaf heap then has to resort to the fungal process.


And that leaves - larger ones in particular clump together in impermeable
layers that are starved of oxygen and impede water flow. Spreading leaves
over the lawn and running the mower over them a couple of times before
mixing in with general stuff and lots of grass clippings in particular works
very well.

pk