Can I Compost Onions and Garlic? Here's What You Should Know
Yes, you can compost onions and garlic. Despite a common gardening myth, onions and garlic are completely compostable in most backyard compost systems. Bulbs, skins, peels, roots, tops, and food scraps can all be added to a compost pile where they eventually break down into nutrient-rich organic matter.
Because onions and garlic have strong natural compounds that slow decomposition slightly, they may take longer to break down than softer fruit and vegetable scraps. Chopping them into smaller pieces helps speed up the process.
Can You Compost Onion Skins and Garlic Peels?
Absolutely. The papery outer skins from onions and garlic are excellent additions to a compost pile. Like dry leaves, they are relatively dry and break down more slowly than the fleshy portions, but they will eventually become finished compost. Cutting larger pieces into smaller chunks helps microorganisms break them down more efficiently. You can compost:
Onion skins
Garlic peels
Whole onions
Garlic bulbs
Onion tops
Garlic stems
Onion roots
Garlic cloves
Why Do Some People Say Not to Compost Onions and Garlic?
This advice comes from several long-standing gardening myths. Some people believe onions and garlic:
Kill beneficial microorganisms.
Repel earthworms.
Prevent compost from breaking down.
Harm finished compost.
Research and practical experience from composters show that these concerns are largely unfounded when onions and garlic are added as part of a balanced compost pile. Like many kitchen scraps, they should simply be mixed with a variety of greens and browns rather than added in large quantities all at once.
Are Onions and Garlic Greens or Browns?
Onions and garlic are considered nitrogen-rich "green" compost materials. Although they may not contain as much nitrogen as fresh grass clippings, they contribute moisture and nitrogen that help fuel microbial activity. Balance them with carbon-rich browns such as:
Dry leaves
Shredded cardboard
Straw
Shredded paper
Wood chips
A balanced compost pile will break down more efficiently and produce healthier finished compost.
Can You Compost Cooked Onions and Garlic?
Yes but with a few considerations. Plain cooked onions and garlic can generally be composted. However, foods that contain:
Large amounts of oil
Butter
Cream
Cheese
Meat
are better kept out of most backyard compost piles because they may attract pests and create odors. If you're composting leftover meals, scrape away heavily seasoned or greasy ingredients whenever possible.
How to Compost Onions and Garlic in a Backyard Compost Pile
A traditional backyard compost pile is one of the easiest places to compost onions and garlic. For the best results:
Chop onions and garlic into smaller pieces.
Mix them with carbon-rich browns like leaves or shredded cardboard.
Avoid dumping large amounts in one spot.
Turn the pile regularly to improve airflow.
Maintain moisture similar to a wrung-out sponge.
Because onions and garlic are nitrogen-rich greens, they should always be balanced with browns to keep your compost pile healthy and odor-free.
Can You Compost Onions and Garlic in a Worm Bin?
Yes but moderation is important. Composting worms can process onions and garlic after microorganisms begin breaking them down, but large amounts may temporarily discourage worms because of their strong sulfur compounds and acidity. If you're vermicomposting:
Add only small amounts at a time.
Chop scraps into small pieces.
Bury them beneath bedding to reduce odors.
Mix them with other fruit and vegetable scraps.
Watch your worms. If they avoid the area, reduce the amount next time.
For households with large quantities of onion or garlic waste, a traditional compost pile is often the better choice.
Can You Bokashi Compost Onions and Garlic?
Absolutely. Bokashi composting is one of the best methods for processing onions and garlic because the fermentation process easily handles foods that can be slower to decompose in traditional compost piles. Simply:
Chop larger pieces if desired.
Add them to your Bokashi bucket.
Sprinkle Bokashi bran between layers.
Compress the material to remove air.
Seal the lid tightly after each use.
Once fermentation is complete, the material can be buried in soil or added to a traditional compost pile to finish breaking down.
Can You Compost Onions and Garlic in a Compost Tumbler?
Yes. Compost tumblers are excellent for onions and garlic because frequent turning helps increase oxygen levels and speeds decomposition. To compost successfully in a tumbler:
Chop scraps into small pieces.
Mix with dry browns like shredded cardboard or leaves.
Avoid overloading the tumbler with wet kitchen scraps.
Rotate the tumbler regularly.
Monitor moisture so the compost stays damp but not soggy.
A balanced tumbler will process onion and garlic scraps much more efficiently than one containing mostly food waste.
Can Worms Eat Onions and Garlic?
Yes, but moderation is important.
Composting worms can process onions and garlic after microorganisms begin breaking them down. However, many vermicomposters avoid adding large quantities because the strong sulfur compounds and acidity may temporarily discourage worms from feeding in that area.
Small amounts mixed throughout a well-established worm bin are generally not a problem. If you have a large number of onions or garlic scraps, a traditional hot compost pile or bokashi is usually a better option.
How to Compost Onions and Garlic Faster
If you'd like these materials to decompose more quickly:
Chop bulbs into smaller pieces.
Separate large clumps of onion skins.
Mix them evenly throughout the pile.
Maintain a balanced mix of greens and browns.
Turn the compost regularly.
Keep the pile moist but not soggy.
The healthier your compost pile, the faster onions and garlic will disappear.
Common Onion and Garlic Composting Mistakes
Avoid these common mistakes:
Adding large quantities all at once.
Composting heavily oily or greasy leftovers.
Forgetting to balance greens with browns.
Expecting onion skins to disappear quickly.
Assuming onions and garlic cannot be composted.
Like most kitchen scraps, moderation and diversity produce the best compost.
Frequently Asked Questions
Can you compost moldy onions?
Yes. Moldy onions are already beginning to decompose and can safely be added to a healthy compost pile.
Can you compost sprouted onions or garlic?
Yes. Sprouted bulbs are completely compostable and break down just like fresh ones.
Can you compost rotten onions?
Yes. Rotten onions are excellent compost ingredients as long as they are free from synthetic packaging or contaminants.
Do onions make compost smell?
Not when added to a healthy, balanced compost pile. Unpleasant odors are usually caused by poor airflow or too many wet nitrogen-rich materials rather than onions themselves.
Can you compost onion roots?
Yes. Onion roots, stems, leaves, bulbs, and skins are all compostable.
Don't Let Onion Myths Leave You in Tears
Onions and garlic deserve a place in your compost pile. When mixed with a healthy balance of greens and browns, these kitchen scraps become part of the natural cycle that transforms food waste into nutrient-rich compost. Instead of throwing them away, return them to the soil and let nature recycle every layer, from papery skins to leftover bulbs, into healthier gardens for seasons to come.
About Let’s Go Compost
Let’s Go Compost is a national nonprofit making composting simple, affordable, and accessible. Our programs bring hands-on composting to communities, helping people turn food and plant waste into healthy soil that supports food systems, native plant ecosystems, and pollinators. Learn more at letsgocompost.org and support our work at letsgocompost.org/donate.
