So, Can You Compost Onions?

Composting is one of the single best things that you can do for your garden, or any other plants you take care of. It allows you to convert what would otherwise be kitchen, household and yard waste into extremely rich, nutritious soil that all plants will love.

onions in the ground ready for harvest
onions in the ground ready for harvest

Composting is a surprisingly delicate process, one requiring the correct ratio of additions, plenty of maintenance and a working knowledge of basic soil chemistry.

Adding the wrong things could bring the progress of your compost pile to a screeching halt, and it is common to see arguments over what is or is not a good addition around the internet.

How about onions, for instance? Can you compost onions?

Yes, you can compost onions so long as they are chopped up to prevent sprouting and added in moderation so that you don’t acidify your pile.

Onions are indeed one of those compost pile additions that seem to garner a lot of arguments. Some people swear up and down that they are just fine, while others report that adding even a single onion to your pile is going to ruin it.

Like so many contentious subjects, the truth is somewhere in the middle, but suffice it to say for now that you can add onions to your compost pile with complete safety so long as you follow a few simple rules of thumb.

I’ll tell you all about those below…

Do Onions Help or Hurt Your Compost?

To be totally clear right up front, onions are good for your compost pile, and safe, so long as you add them in properly.

I’ll tell you what you should do and what you shouldn’t do below, but for now just accept that onions will decompose and nourish your pile like any other veggie.

So long as you are willing to do these few simple things there is no reason you can’t put onions to work in your compost. Don’t believe any screaming to the contrary.

Can You Compost Onion Peels?

Yes, you can compost onion peels. In fact, you can add onion peels to your compost even if you aren’t adding any other parts of the onion.

Most people remove the thick, tougher outermost layer of an onion that is just beneath the papery skin when cooking with it, and this can make a great addition to your kitchen compost bag prior to sending it out to the main pile.

Can You Compost Onion Skins?

Yes. The translucent papery skin of an onion is 100% safe for putting in your compost pile. It isn’t good for anything else, so you might as well get some use out of it!

Can You Toss Whole Onions in Your Compost Bin?

No! If you’ve ever held on to an onion too long, you probably noticed they have a tendency to sprout and begin growing, even if they are sitting in your produce basket or just lying around on the counter.

Believe me; a whole onion will do the same thing in your compost pile once you bury it. This could mean significant disruption of your compost over time, and in any case, an onion that is growing is unlikely to decompose.

Again, don’t put whole onions in your compost pile!

Chop Up Onions to Keep Them from Sprouting

Now, there is a simple solution to the problem of whole onions discussed just above: Just chop them up! Even a rough, large chop is sufficient to prevent an onion from sprouting once it gets buried inside your pile.

That’s it. It doesn’t matter how you slice it or chop it so long as it is totally chopped.

I wouldn’t just cut it in half and trust that it won’t sprout, but even cutting it into eighths or perhaps a little bit finer should be more than sufficient to ensure it will decompose and normally in your pile.

Caution: Onions are Quite Acidic, May Change Compost pH

Something else to be aware of, and one allegation leveled against onions by haters that has a basis in truth, is that they are quite acidic.

They are so acidic, in fact, that they can disrupt the pH balance of your compost pile, and this can prove to be disastrous if you are going with the tried and true alkaline approach for your compost.

However, where people go wrong is assuming that even a single onion is somehow acidic enough to completely spoil an entire compost pile. That’s just wrong, and it will not happen.

Adding a whole bunch of onions will definitely change the acidity of the pile, but the occasional onion, chopped up and properly mixed into the pile, is no problem at all.

You shouldn’t be adding onions every day or adding significant quantities every week, but a periodic inclusion is no problem.

Even then, there is another super simple trick you can do to offset this acidity. I’ll tell you about it in just a minute.

Bury Onions Deeply in Compost to Keep Odor to a Minimum

Something else you’ll want to do when adding onions to your compost pile is bury them good and deep when you add them. I recommend a minimum of 12 inches (30 centimeters), or as deep as you can go if your pile is small.

Why? Simple: onions really stink! They will stink dreadfully when they begin to decompose unless they are totally buried. I can promise that you don’t want to be putting up with that odor.

Adding Some Shredded Paper or Cardboard Can Also Help with Odor

If you don’t have the depth to spare in your compost pile or just want to hedge your bets against truly noxious odors, tossing a little bit of shredded paper or cardboard with the onion when you bury it.

It won’t impede decomposition, but it will help to tame the worst of the odor.

Crushed Eggshell Works to Counter Onion’s Acidity

I mentioned it just a moment ago that onion is indeed quite acidic, and adding too many onions or playing it fast and loose with the pH balance of your compost pile might be a recipe for the whole thing losing its alkalinity.

If you don’t want to worry about the acidity of onions so much when you are adding them, all you need to do is keep a few eggshells from your kitchen and crush them up, adding them in with the onions at the same time.

The alkalinity of the eggshells will counteract the acidity of the onion.

Can You Compost Wild Onions, Leeks and Chives, Too?

Another obvious question, since we’ve established that you can in fact add onions to your compost pile safely, is whether or not its relatives are also safe to add things like:

  • wild onions
  • leeks
  • chives
  • garlic
  • and so forth

The answer, happily, is yes. all of the above are also safe to add to your compost pile but you should treat them like onions…

Keep an eye on the pH balance of the pile, try to offset the acidity when you add them, bury them so they don’t stink and make sure they are chopped up good so they don’t sprout.

Nothing to it, and now you know enough about onions and their cousins to put them to work in your compost pile without worry.

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