I set up a 7 cu ft rolling composter in my garden about 3 weeks ago and filled it about halfway with 1/3 food scraps and 2/3 cardboard/leaves/finished compost. My kids added more food scraps, so it's probably 50-50 now. I've kept it wet and turned it, but upon opening it yesterday, it had a sour stench and a lot of bugs squirming in it. I added more finished compost, hoping it just had too much food scraps, but I'm not sure if that's the right thing to do. Is it just 'not done' yet?

Any advice?

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    Have a look here: Speeding up decomposition of sickly sweet smelling giant compost heap & here: Should I add water to my compost heap?. Also please define "food scraps", what exactly makes up that part of your compost pile? Is your compost pile open to the elements or is it closed (sealed inside some sort of container)?
    – Mike Perry
    Sep 12, 2011 at 17:38
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    Food scraps for us are vegetable peelings, fruit rinds and old fruits/vegetables. I've read about limiting meat or bones, so I didn't add any at all.
    – RichardG
    Sep 12, 2011 at 18:42
  • Meat and bones don't belong in a compost pile (IMHO), doing so it a sure fire way to attract vermin...
    – Mike Perry
    Sep 13, 2011 at 2:25

1 Answer 1


If it has a sour smell, you've probably got:

  • Too much nitrogen, not enough carbon -- add more cardboard & leaves. Avoid adding food scraps, lawn clippings, etc until the problem is fixed.
  • Not enough air -- turn it.
  • Too much water -- don't add any more water. (This also contributes to "not enough air" -- when it's too wet, the bacteria can't breathe.)

If you use just shredded cardboard (which has a very high carbon percentage), I'd add about 10% the volume of the bin to get it to equilibrium. If you use leaves instead of cardboard (high carbon, but not as much), I'd triple that.

This is a rough, off the cuff guesstimate. You'll have to add the cardboard, turn it, let it sit for a couple of days and observe. The cardboard will also soak up some of the excess moisture. If the smell goes away and the pile starts to heat up, then you've got the ratio about right. If it still stinks, add more carbon (leaves or cardboard), turn, and wait another couple of days. If the smell goes away but it doesn't heat up, you may have gone too far with the carbon. This is easier to fix than too much nitrogen: start adding kitchen scraps gradually.

If you have a readily available carbon feedstock (aka "browns": newspaper, cardboard, dry leaves, sawdust, etc), tell your kids that they need to add some whenever they add kitchen scraps. The "browns" belong on top of the scraps. Use more leaves, less sawdust -- the chart on this page will give you an idea of how much carbon is in various ingredients. (But your own experience will be the best teacher.) A thin sprinkling of garden soil over the top of the browns helps inoculate the compost with good bacteria and trap nitrogen from escaping into the environment.

(As a side note, "bugs" are expected in your compost -- they're part of what will break it down. But it's possible that you've got more than you should. They will probably go away when you get the mix right, especially if you bury the scraps under browns as described above.)

  • "chart on this page" -- I think is missing a link...
    – Mike Perry
    Sep 12, 2011 at 18:00
  • +1 This pretty much fits all our problems with our compost barrel. Not turning is laziness on my part, but for the past year or so I've put less water in (it used to get in via coffee press/cafetieres) and tried to put more leafy matter in. It does help. Bugs are partly a symptom of decomposition (a Good Thing) and the birds will quickly finish them off when you empty the compost out.
    – winwaed
    Sep 12, 2011 at 18:08
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    Our compost container is a rolling tumbler design, with holes in the sides. Thanks everyone for the advice, I'm starting to think my problem is not enough leaves or other carbon, and possibly too much water. The design of this container has holes in the side for air, but it doesn't appear to have a drain for water and I think I've created quite a soup in there. This is my first attempt at composting, so thanks everyone for this and any future advice. I'll try adding more carbon and report back in a few days on my progress.
    – RichardG
    Sep 12, 2011 at 18:45
  • @Richard: if you've got a lot of water (if it is sloshing when you turn it), you may want to try to drain it somehow. I don't use a tumbler, but I'd expect it to stay wetter than open piles, so if you read advice (especially from me, on this site) to hose down your compost, you can probably ignore it. Especially since you're adding kitchen scraps, which in my experience are already quite wet to begin with.
    – bstpierre
    Sep 12, 2011 at 20:48
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    @bstpierre I used to try and drain our barrel composter (moulded plastic thing) by leaving it with the bigger holes downwards. This wasn't very effective as the compost would clog the holes. I found it more effective to find the source of the water (coffee grounds in my case) and avoid putting it in - or adding only if it is dry. for another source of carbon, I also use shredded paper - but sprinkle it in so you don't get one big wet paper mache mess!
    – winwaed
    Sep 13, 2011 at 3:08

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