Can you compost onions? This is a great question. We often buy a bag of onions instead of just one or two because we use them so often. Needless to say, we have a lot of onion scrapes and an occasional onion or two that is not so fresh. So, instead of trashing onions or their remains, can they be add to the compost pile?
Composting Onions – Potential Concerns
You can compost onions but they often present a terrible smell as they decompose. You should be prepared to deal with this odor when you are near the compost. It is best to bury the onions deep in the compost bin (about 12 inches deep) to help deter the smell. You many need to rebury them if you turn your compost.
A potential bigger problem with composting onions is that the smell tends to draw in pest. If these pests gain access to your compost bin, you can potentially have a big mess on your hands. Animals such as raccoons or rodents can quickly become a big nuisance to your composting area if you are not careful.
An additional concern with composting onions is that they can grow new onions. If you have ever held on to an onion for some time, you might have witnessed it start to sprout and potentially grow roots. This is a good thing if you want to regrow onions, but it may not be ideal for your compost. After all, you are looking to create compost and not a comfortable environment for vegetable growth at this point. To avoid new onions from growing, chop up the onions a couple of times over their length and width.
The key to successful compost is getting your ratio of carbon ingredients to nitrogen ingredients correct. Carbon ingredients are commonly referred to as browns. These are materials such as straw, dried leaves, paper towels, and sawdust. Nitrogen ingredients are knows as “greens”. These are your vegetables (onions), coffee grounds, eggshells, fresh grass, and more. You are looking for a 30 to 1 ratio of carbon to nitrogen for the best results. Check out this article from Modern Farmer, which provides a nice guide to achieving compost success.
You should think of onions as one component of a large mix of ingredients for your compost pile. While there are some concerns with using onions as outlined above, you probably should not overthink it. Go ahead and use onions along with a variety of other ingredients to achieve the ideal carbon to nitrogen ratio. Onions are a great addition to compost as long as you take the proper steps to preparing them and placing them in the compost pile. We wish you success in your journey to create quality compost!