My wife and I decided to try composting and after filling a five gallon bucket in three weeks with kitchen scraps we took the jump and bought a two-chamber tumbler (so we can add to one side while the other is composting). After adding in some more leaves and grass and scraps one barrel between half and two thirds the way full. I know I want to aerate it by turning, so I need some room for the food to tumble, but how much? Can I continue filling the active side, or should I move to the other side. I get the feeling I'm balancing between wanting as much mass as possible (to retain heat) with being able to effectively aerate the pile.

2 Answers 2


The beginning of the composting process is a period where the material will shrink in size pretty dramatically. It is common for a pile to end up 1/3 smaller. In your situation of adding material slowly, however, a fair bit of the shrinking has already occurred by the time you are adding the last bits that "top off" the tumbler.

A few thoughts:

  • The fuller the tumbler the more you'll have to turn to get it mixed well.
  • If it seems it's not getting mixed enough because it's too full you can take some material and move it to the unfilled half.
  • As always, it's best to experiment and find what works for you, your inputs, and your equipment :)
  • Be sure to toss in some handfuls of rich garden soil to ensure you have the microbial life necessary to compost.

You don't need to leave much space at all; the contents will start to degrade and as they do, they shrink down and take up less room. You might not be able to move the mass inside much by turning initially, but you soon will be able to. Just don't overfill, and by that I mean to the extent that you cram stuff in and it's difficult to get the lid back on because it's too full, you need a little headroom in there.

You can continue to fill the active side in the meantime, and turn it even if it's not yet full.

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