Can You Compost Onions?

Last Updated on March 11, 2022 by Grow with Bovees

Organic compost is a healthy addition to your soil, plants, and vegetables.

This type of organic matter composting process provides a good balance of nutrients to your plants without adding harmful chemicals.

You can also add kitchen scraps to organic compost piles such as leftover fruit and vegetable skins, which leads to the big question. Can you compost onions?

Onions (Allium cepa) can be added to compost bins, but should be added with caution or avoided altogether, and here’s why!

Why You Shouldn’t Put Onions in Compost?

Composted onion is just as valuable as any other type of organic material or food waste with a few caveats. Similar to the properties of potatoes, where their spuds tend to grow and become more potatoes instead of an organic mixture, onions also want to grow, developing new shoots when added to compost, especially in excessive amounts.

Adding to this, compost heaps already emit noxious smells and adding onions simply adds to the unpleasant aroma. Just imagine the smell of rotting onions!

Another reason many people are hesitant to compost onions, is that onions, when chopped up, release very volatile and reactive sulfur compounds (reason for the tears and odor), which can be harmful to the microorganisms in the compost bin.

Onions also have a relatively low pH, hence this acidic nature is why most people don’t add them to compost heaps. If you want to lower the pH levels in your finished compost, you should add onion peels to your compost bin rather than whole onions.

According to The University of Arizona Cooperative Extension, onions peels and scraps do not negatively affect the microbes present in your compost, but it’s recommended that you add these garden annuals with caution.

Onions are a strongly odorous aromatic food, and due to this strong smell can attract pests and wildlife to your already smelly compost bin.

Owing to the foul smell from rotting food matter, your compost bin is already at a big risk of attracting uninvited guests, therefore it’s important to bury odorous foods such as onions at a depth of 10 inches or more in your compost heap.

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Benefits of Composting Onions

There are myriad benefits of adding onion peels to your compost bin, starting with improved quality of soil for healthy plants.

Research indicates that a mixture of onion waste and bovine matter has positive effects on the soil. Onions also balance soil pH with their acidity and greatly improve soil structure for roots to grow and absorb other nutrients such as water.

How to Compost Onions?

If you’re going to add onions to your compost tumbler, it’s best to compost onion peelings and skins, not whole onions.

You shouldn’t attempt to compost onions that are whole, but first, chop the entire onion up into smaller pieces, or else the decomposition process will be a lot longer.

This compost process rule applies to all types of large household kitchen waste, everyday kitchen scraps, and everyday kitchen waste such as bulbous vegetables, and popular vegetables.

If you are vermicomposting, which is a compost breakdown process that involves certain species of earthworms to enhance the process of organic waste conversion, then do not add onions to the compost pile.

Worms do not like to munch on odorous foods such as onions, hence are unlikely to break them down in the worm compost heap. Other foods that are less likely to be consumed by worms are potatoes, broccoli, and garlic.

Odors are always a concern whether you’re creating a traditional compost pile, vermicomposting, or worm composting, and composting onions won’t help this situation.

You can add certain things to help control and/or eliminate odor in compost piles such as shredded paper and cardboard, egg shells, and/or mussel shells. Adding crushed oyster shells also helps.

You can try soaking onion skins in water to reduce their pungency and odor, or in vinegar or citrus juice to add a new flavor before adding them to your compost tumbler.

Another area of concern when composting onions and onion scraps, is the onset of pests and insects like rats and flies, but a few simple tweaks can eliminate these things. Always be sure to cover your compost bin through the entire process to avoid flies that are attracted to onions, such as vinegar flies.

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Furthermore, avoid putting meat products in your compost tumbler to eliminate smells, and keep rats and mice away.

Can I Compost Onions In Bokashi Compost Bin?

Bokashi composting is one of the most popular ways to recycle kitchen food scraps, and is an anaerobic process that uses inoculated bran to decompose kitchen waste including dairy and meat and vegetable scraps. You can put onions in your bokashi bin along with other items including citrus peel, onion, and coffee grounds and coffee filter papers.

The Key to Composting Onions, Dry Matter, and Organic Matter is All About Balance

Sometimes it may be a bit challenging to get the right balance in your compost heap. You need a good balance between nitrogen (moist green’ materials like garden clippings, onions, other types of vegetables and fruit scraps, and carbon (dry brown’ materials like cardboard, paper, and dry leaves).

Composting is a step-by-step process, and the end result is either it’s usually too dry or too wet.

What Type of Onions Should You Avoid Putting in Your Composting Bin?

Onions that have been ruined by onion mildew, leaf blight, or white rot shouldn’t be added to your compost pile. You can instead burn the diseased rotting onion and add the ash to your compost heap.

You can also compost moldy onions  because mold is a fungi, and has beneficial properties to break down extreme amounts of organic matter.

However, adding cooked onions is a big no-no because they do not break down easily due to the grease and fat. And what’s even worse is that this fat and grease can easily spread over the other valuable nutrients and prevent them from composting.

How to Add Onion Compost to Soil Including Clay Soils, Healthy Soil, and Damp Soil

In most cases, compost is added to your garden to prevent soil compaction, and improve overall soil structure. The most effective way to add onion compost to improve soil quality is by digging the compost in.

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Digging the compost in is especially important for sandy soils, clay soils, or a layer of soil that lacks organic matter.

If you have healthy rich soil and are just trying to maintain it rather than remediating it, you don’t need to dig the compost in the container with soil but can spread the compost on top.

You can also spread compost over the grass in your lawn in no more than 1/4th of an inch layer, and the worms and other organisms will do the rest.

Although garden soil with nutrients contains roughly 5 percent organic matter, you can mix 20 percent of compost to 50 percent soil for plants in pots and containers including the base of tomato plants, diseased plants, and even healthier plants.

What Organic Scraps Are Good for Compost Heaps?

There are a few things that you should never throw into your compost heap for the sake of better compost. Tea and coffee bags add large amounts of nitrogen, phosphorous, and potassium to the pile, which are great for plant health.

But you should remove the bags before adding the coffee and tea because some coffee and tea bags contain nylon and other synthetic fibers that do not break down during the composting process..

Fish and meat scraps decompose just fine in a compost pile, but, as mentioned earlier, are a magnet for rats, raccoons, and other pests in the area. You can shred cardboard and add it to your compost heap, but remove the tape and glue, as these things won’t decompose properly.

The major thing that you should avoid throwing into your compost is anything containing plastic, such as straws, bottles, and wrappers. These plastics are difficult to break down in the composting process. Instead, you should use paper grocery bags, newspaper, cardboard, and wood fiber products like sawdust.

Hopefully, our answer to can you compost onions?, has proved beneficial to you.