A smelly compost pile generally comes down to one issue: anaerobic conditions in the pile. This can be caused by a few things. We'll go through each possible cause, and then we'll look at ways to fix your compost pile and get rid of the stench, for good.
Cause #1: The Pile is Too Wet
A wet pile is easily one of the most common causes of smelly compost. If the pile stays too wet, the beneficial microbes that break down the pile can't do their job, and you get a decaying, putrid odor to the pile instead of the sweet smell of good compost.
To fix a wet pile, there are a couple of things you can do:
- Turn the pile. Turning the pile will aerate it, which will help it dry out some and provide oxygen to those beneficial microbes to get them working again.
- Add more "browns." "Browns" are the carbon-rich materials we add to a compost pile, and they tend to be much drier in nature than "greens." Some good browns to add include straw, dried leaves, or shredded newspaper. Mix it in well, and your pile should start smelling better.
- Cover your pile. If the problem is that it's been raining and your pile is sopping wet, give it a turn, add some browns, and cover it with a tarp for a while to prevent more water from making your pile even soggier. Once it dries out some, you can take the tarp off.
Cause #2: Too Many Greens
This issue is linked to having a too-wet pile. "Green" materials in composting terms are nitrogen-rich materials such as grass clippings, vegetable and fruit scraps, and used coffee grounds. Because these materials naturally contain so much water, they can easily become matted down and make your compost pile a soggy, smelly mess.
To fix the issue of having too many greens -- add some browns! Add shredded newspaper, straw, and pine needles to the pile. Mix it all together well.
Cause #3: Meats, Fats, and Dairy
While you can technically compost anything that was once alive, composting meat, fats, and dairy is a bad idea. Not only does it cause odors (anyone who has smelled spoiled meat knows how bad the stench can be) but it also attracts animals such as dogs, cats, and rats. Keep non-plant matter out of your bin, both for odor and safety reasons -- compost that has had meat and other spoiled foods in it can harbor harmful bacteria, and you don't want any of that in your compost. If you want to compost meat and dairy, look into Bokashi composting.
Tips for Keeping Your Compost Pile From Smelling Bad
There are a few general rules to composting. If you follow them, you shouldn't have many problems with odors:
- Mix greens and browns. A good ratio is 3 parts brown to one part green. This will help keep your pile from becoming soggy and is a good ratio to get the most activity from those beneficial, compost-making microbes.
- Small pieces are better. If you can chop or shred things like leaves and vegetable scraps, that will help them break down faster and reduce the chance that your pile will turn into a moist, matted mess.
- Turn it. Some people obsessively turn their compost every couple of days. If you can get out and turn your compost once every week or two, that's good enough. Turning adds oxygen to the bin, which will result in a better-smelling pile and faster compost production.