Let’s start with the basic ground rule of composting: your pile should not smell bad. It can occasionally smell “earthy” or even fruity if you’ve dumped in a lot of rinds but an unpleasant smell is a sign that something is out of balance.
Sour or Ammonia Smell
This one was learned from personal experience as we’ve gotten to know our enclosed composting bin. This small bin holds 65 gallons so it’s just slightly bigger than a large hard-sided garbage can. You’d think that’s too small but after two weeks of just dumping in our household food scraps and odds and ends from trimming and weeding in my gardens, we barely had a few inches of compost cooking. So, the husband decided to get things moving by adding lawn clippings. Like three mower bags full of lawn clippings.
And that’s how we learned: compost mixture should be two to three parts browns (leaves, sawdust, wood shavings, shredded newspaper) to one part greens (veggie scraps, trimmings, grass, etc.). It’s best to layer greens and browns and mix them thoroughly after each layer and always top off the pile with a layer of browns.
Luckily, we are currently “grandparents” to a dozen baby chickens so our son brought over a big bag of their bedding (wood shavings). This was the perfect browns mixture to fix our problem plus we got an extra dose of super starter, chicken manure. I know, the things you learn when composting! Within 24 hours, the smell was gone!
Sulphur or Rotten Egg Smell
This smell is caused by a lack of oxygen so it tells you the pile is not decomposing properly (or anaerobically). This can also be caused by a too large input of greens – especially grass – as it can become matted and compacted too thickly to allow oxygen to work through the layers. Again, adding browns in layers and mixing well will stop this smell.
Also, make sure your compost pile has sources of air inflow – either through slits in the side of the bin or an open top. You should also aerate your compost pile by stirring it every few days when you first start out and then every week or so after it ages for a while.