Can You Compost Onions? Tips For Adding Onions To Compost

Onions are common kitchen scraps found in many homes. Their versatility in cooking has made them a must-have ingredient. From soups and stews to salads and sandwiches, onions add delicious flavor to various dishes.

But what do you do with onion scraps after all that slicing and dicing? Can you put them into your compost pile or bin?

The short answer is yes, you can put onion scraps in your compost. However, there are some things you need to know before doing so.

Why compost onions?

Composting is the process of converting organic waste like food scraps and yard debris into fertile soil. Gardeners use compost as a natural fertilizer and soil amendment.

Onions are considered greens in composting. Greens refer to nitrogen-rich materials like fruit and vegetable scraps, coffee grounds, and fresh grass clippings. Greens provide nitrogen, an essential nutrient for healthy compost.

Browns are carbon-rich materials like dried leaves, twigs, sawdust, and shredded cardboard. Browns supply carbon, another key ingredient in compost.

A balanced mix of greens and browns helps create ideal conditions for beneficial microorganisms to break down the waste. The end result is nutrient-dense compost to nourish your plants.

So at first glance, it would seem totally fine to throw onion skins, ends, and trimmings into the compost bin. But there are a few potential drawbacks to consider before doing so.

Dos for Composting Onions

Properly composting onions requires a few key steps to overcome their challenges. Here are the steps for composting onions effectively:

• Chop or dice onions: To speed up the composting process, chop or dice the onion peels, ends, and any spoiled onions before adding them to the compost pile. Smaller pieces break down faster and prevent the compost from becoming compacted.
• Mix with other compostable materials: Create a well-balanced compost mix by combining the onion scraps with a variety of other compostable materials. Include a mix of green materials (e.g., vegetable scraps, grass clippings) and brown materials (e.g., dry leaves, straw) to maintain the right carbon-to-nitrogen ratio and promote efficient decomposition.
• Layer or mix compost ingredients: As you add onion scraps to the compost pile, alternate them with other compost materials. Layering or mixing the ingredients ensures better aeration and allows for an even distribution of moisture and microorganisms throughout the pile.
• Maintain moisture levels: Onions have a high water content, which can contribute to the overall moisture level of the compost. However, it’s essential to monitor and maintain proper moisture levels in the compost pile. The compost should feel like a wrung-out sponge—damp but not soggy. Regularly check the moisture and adjust as needed to facilitate decomposition.
• Turn the compost pile: Regularly turn or aerate the compost pile every 1-2 weeks. Turning the compost helps distribute oxygen, which is crucial for the activity of aerobic microorganisms responsible for breaking down the compost materials. It also helps prevent the compost from becoming compacted and smelly.
• Use mature compost. Allow the composting process to complete fully before using the compost in your garden. Mature compost is dark, crumbly, and has a pleasant earthy smell. If you can still identify onion scraps in the compost, it’s not fully mature, and you should wait before using it on your plants.
• Compost in a bin or enclosed system: If you’re concerned about attracting pests or animals to your compost pile due to the onion scraps’ smell, consider composting in a closed bin or enclosed composting system. These systems help contain odors and deter unwanted visitors.
• Follow composting guidelines: Familiarize yourself with composting guidelines specific to your region or municipality. Some areas may have regulations on what can be composted, and certain composting methods may be more suitable depending on your climate and available space.

Don’ts for Composting Onions

To avoid potential problems, here are the don’ts when composting onions:

• Don’t compost large onion pieces. While it’s beneficial to chop or dice onions before composting, avoid adding large chunks or whole onions to the compost pile. Whole onions take longer to break down and may attract pests or rodents to the compost.
• Don’t add cooked onions or onion-based dishes. Composting cooked onions, onion soups, or other onion-based dishes is not recommended. Cooked foods may introduce fats, oils, and seasonings that can disrupt the composting process and attract unwanted pests.
• Don’t use only onion scraps. Composting works best with a diverse mix of materials. Avoid adding only onion scraps to the compost pile. For optimal composting, mix the onion scraps with a variety of other compostable materials, such as fruit and vegetable peels, coffee grounds, yard waste, and shredded paper.
• Don’t add large quantities at once. Adding a large amount of onion scraps all at once can create an imbalanced compost pile. This may lead to foul odors, slow decomposition, or the attraction of pests. Instead, add onion scraps gradually as you generate kitchen waste.
• Don’t compost diseased onions. Avoid composting onions that show signs of disease or rot. Adding diseased plant material to the compost may spread the pathogens and lead to contaminated compost.
• Don’t forget to cover onion scraps. If you’re composting in an open pile or bin, cover the onion scraps with a layer of other compost materials to reduce the risk of attracting pests and to control odors.
• Don’t neglect aeration. Proper aeration is essential for composting. Avoid compacting the compost pile, as this can lead to anaerobic conditions, slowing down the decomposition process and causing unpleasant odors.
• Don’t use immature compost. Using compost that has not fully decomposed can be detrimental to plants, as it may still contain compounds that can harm young roots or inhibit seed germination. Make sure your compost has fully matured before applying it to your garden.

By keeping these “don’ts” in mind, you can ensure that your composting process remains efficient, odor-free, and produces high-quality compost that benefits your garden and the environment.

Benefits of Composting Onions

Composting onions provides key nutrients, enhances soil quality, boosts microbial activity, helps suppress plant diseases, reduces food waste, and is simple to do. Following best practices ensures effective onion composting.

Here are some key benefits of composting onion scraps:

• Provides Nutrients: Onions contain nitrogen, potassium, phosphorus, and trace minerals that enrich compost. These nutrients feed microorganisms and fertilize plants.

• Improves Soil Structure: The organic matter from composted onions helps improve soil texture, create air pockets, and retain moisture. This promotes healthy root growth.

• Increases Microbial Activity: As onions break down, they feed beneficial bacteria, fungi, and other microbes in the compost and soil. More microbial life aids plant health.

• Suppresses Diseases: Onions have antifungal and antimicrobial abilities that can help protect plants. Composting can maintain these properties.

• Reduces Waste: Composting onion scraps keeps them out of landfills and gives them a second life as fertilizer. This supports sustainability.

• Easy Process: Composting onions takes minimal effort when mixed properly into piles. It’s an easy way to reuse food waste rather than trash it.

The Downsides of Composting Onions

Onions have several qualities that give some gardeners pause when it comes to composting them:

Strong Odors

Onions have a pungent, lingering scent even after they’re chopped up. Adding a lot of onion waste to an imbalanced compost pile can make it stink. The smell comes from sulfur compounds in onions.

Excess greens generate ammonia gases during decomposition. Ammonia has a potent stench that many find unpleasant. Too many onions may exacerbate unpleasant odors in the compost heap.

Attracts Pests

The strong smell of onions can also attract pests to your compost bin. Rodents like rats and mice may scavenge for discarded onion pieces. Raccoons, opossums, squirrels, and foxes may also dig through the compost looking for tasty morsels.

Insect pests like houseflies are highly attracted to the sulfurous volatiles given off by onion waste. They may swarm compost piles and bins with too many onions added.

May Harm Plants

Onions have antimicrobial properties that suppress diseases and kill pathogens. But these same compounds can potentially harm plants.

Too many onion skins in immature compost could damage plant roots or inhibit seed germination. The impacts depend on the onion variety and quantity added.

So raw, unfinished onion waste directly mixed into garden beds or potting soil may cause issues. Finished, cured compost likely poses few problems.

Can you compost red onions?

Yes, you can compost red onion skins, scraps, and trimmings. Chop the onion waste into small pieces and mix them into the center of the compost pile. Bury under 10 inches of compost material to contain odors. Composting red onions works best in well-aerated outdoor bins, not enclosed composters.

Can you compost spring onions?

Spring onions, or scallions, are excellent candidates for composting. These mild-flavored greens can enrich your compost with essential nutrients. As with other onions, chop them into smaller pieces before adding them to the compost. Spring onions have a milder aroma, but it’s wise to cover your compost to prevent unwanted pests.

Other Vegetable Waste Options

If you want to minimize onion waste in your compost, consider substituting it with other vegetable scraps.

Potato Peels: Potatoes provide lots of carbohydrates for compost microbes to munch on. Thoroughly mix the peels with the other ingredients.

Carrot Scraps: Carrot stems, leaves, and skins add beneficial nutrients. Chop up before adding to the pile. Don’t put too many carrot pieces on top.

Broccoli Stalks: Coarsely chop up stalks after harvesting broccoli heads. They decompose fairly quickly in compost.

Cucumber Peels: Cucumber skins provide moisture and nutrients. Just don’t overload the pile with too many at once.

Corn Cobs: Break corn cobs into smaller chunks before composting. They take quite a while to fully break down.

Sweet Potatoes: Cooked sweet potato skins and flesh compost well. Raw peelings may take longer to decompose.

Pumpkin Guts: Pumpkin innards are rich in nitrogen. Mix the pieces into the center of the pile. Don’t leave clumps sitting on top.

Melons: Watermelon, cantaloupe, and honeydew rinds compost nicely. Chop large pieces first for faster decomposition.

What Not to Put in Garden Compost

Some food scraps aren’t recommended for backyard compost piles.

• Meat, fish, and bones
• Dairy products
• Oils, grease, butter, and margarine
• Salts and sauces
• Baked goods with frosting or sugar
• Cheese, eggs, and mayonnaise
• Sauerkraut and kimchi
• Processed foods

These materials can attract rodents and flies or impede the composting process in small home systems. They also take a very long time to break down.

Other items to avoid putting in garden compost piles include:

• Weeds with mature seed heads or invasive roots
• Diseased plant materials
• Pet waste or litter
• Yard trimmings treated with herbicides
• Glossy magazines or colored paper
• Sawdust from pressure-treated lumber

Following basic composting best practices helps create a healthy decomposition environment. Always use caution and moderation when adding onion waste to your compost. With some extra monitoring and care, you can safely turn onion scraps into valuable organic matter for your garden.

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