Black Mold On Onions

black mold on onion *Sorry for the fuzzy photo. My camera just wouldn’t focus!

A few weeks ago I decided to harvest all of my onions, as the tops were all dead, and I wanted to clean the garden bed out. I put them in a basket and sat them on a shelf in my kitchen.

Yesterday, I was making dinner and the recipe called for onions. Oh good, I’ve got some of those! I pulled them out and began peeling back their flaky outer layers. As I prepped them for the cutting board, I began to notice that every one of the onions I had peeled had this black stuff on it, underneath the skin. I figured it was just dirt, no big deal, so I washed it off and kept peeling more onions.

I was about to start chopping the onions up, when I started to wonder about those black spots. I wasn’t so sure it was just dirt. I mean, if it was dirt, why was it underneath the layers and not simply on the surface? I hopped on the internet and searched for black spots on onions. Sure enough, I quickly discovered what it really was: Aspergillus Black Mold.

Evidently, it’s a pretty common fungus among home grown onions in particular. It comes from the onions getting too hot or humid while being stored. Maybe I should have stored them in the fridge? I definitely should have allowed them to dry well before storing though.

It was really hard throwing away all of my onions. I was so tempted to just wash them off and use them! *Sigh* But of course, it wasn’t worth the risk of making my family sick. Oh well. At least the pig enjoyed them!

About Kendra 1096 Articles
A city girl learning to homestead on an acre of land in the country. Wife and homeschooling mother of four. Enjoying life, and everything that has to do with self sufficient living.


  1. I’ve found black mold on my onions from the store. It was not only in the layers, but the center. After reading this, I knew I had to just toss them. Shame though, the family likes onions with their tacos. I didn’t want to risk anyone getting sick though..

  2. We use mildly molded onions anyways; but they can go fast once the mold starts. I toss the outer layers, wash thoroughly… and honestly, I tend to cook onions for a very long period anyways: things like spaghetti sauce and the onions thicken it up nicely.

    Onions are one of my best crops here in the low desert of CA. They like sandy poorer soil with good drainage. Not alot of humus or manure. I don’t plant them after grass or wheat, as it tends to encourage the molds. Fresh manure is not good for them. Wait at least a year after applying manure, if you can, before planting onions. Side dressings of Blood meal and bone meal are much better. They need enough nitrogen to get healthy leaves, which result in large bulbing later; but too much and the plants get disease. They really are a great desert crop for that reason.

    I dry mine a few days (or up to a week) above grade, leaves and all atop the dry garden bed. Then I lay them out in layers on old nursery flats and move them to air dry some more in the garden shed, sheltered from direct light and moisture. Once the necks are fully cured and dry, I know it’s safe to put them in crates (like milk ones that let air through) and store in my dry garage. They will keep for at least three months for me that way. Some will even store many months more; but some sprout, some mold (and must be used or tossed immediately or it spreads). I go through the boxes every few weeks to cull out those. Dixondale Farms in TX has a great website and explains it all pretty well. I often buy their onion plants to save on the water necessary to germinate the onions in the summer months; since onions are my winter crop here. I plant sometime after the first rains in Nov, up until mid January. Harvest is sometime in June. Nature decides that one. I begin culling out around Easter, so I can get bigger onions in June, and so we can begin enjoying the harvest.

    Your climate is different from mine; but this may give you an idea of how to grow them better. Oh… as I cull, I make a few extra big spots and insert watermelon or butternut squash seeds or plants. I find the rotation works well. I’ve tried planting with lettuce and it works, but the onions seem to suffer a bit. But if I’m short on space I’ll do it anyways. They seem to do well following my yard long pole beans; but sometimes I’m too lazy to pull out the trellis.

  3. I always put my onions (and potatoes) on a big blanket/sheet/etc and leave them in the sun for a few days. I’ve had some mold problems, but it’s mostly in the spring after they’ve been in the basement all winter. I don’t think you store them in the fridge. I would recommend that you go to the library and check out some books on storing food, canning, etc. Don’t reinvent the wheel all the time – use the knowledge others have gained through the years.

    • Susan,

      I figured the fridge was a good idea ’cause everything I read suggested that the onions be stored between 34* and 40*. BUT, from what I’ve read since posting this it seems that the problem was more that I didn’t allow them to dry properly before storing. Carla Emery (Encyclopedia of Country Living) suggests that the onions be set in the sunshine for three days or so before bringing them in; then storing them in a cool, dry place in a cardboard box.

  4. Hmmm, that’s interesting because we just peel that layer off and continue to use the onion. That’s what my grandfather always did and he was a life long farmer. We’ve never been sick and I’ve never made my family sick by doing this. My pap always said that stuff was only on the first layer and it didn’t mean the whole onion was bad. I guess I’ve never given it a second thought! But this is also coming from a woman that lets her kids lick the brownie batter spoon! Ha!!

    • Tabatha,

      Really? See, that’s totally what my first inclination was to do. It was only the first layers. I hated to toss the rest of the “good” part away. After reading more about this mold, it doesn’t seem that it’s very toxic, even when exposed. You might get a headache or something, but it’s not going to kill you. Hmmm… I guess if things get bad enough we will take the risk and just eat the good parts. For now, life didn’t depend on those onions, so it wasn’t complete tragedy losing them. Thanks for the info though! It’s good to hear advice from those who’ve done otherwise.

  5. I’m with Tabitha on this one, I just peel that layer off, wash and use the onion, we’ve never been sick or had any problems.

    Tabitha, I lick the brownie batter spoon too!!!


  6. This has happened to me before as well. After all that hard work growing them and then you have to throw them out. But I’m glad the pig enjoyed them. 🙂

  7. When I harvest onions, I tie them up in bundles and hang them from the rafter on the porch of the garden shed. They’re out of the rain and direct sun, have plenty of air circulating and dry very quickly. And it’s sort of pretty 🙂 We’ve had lots of 90 degree weather and high humidity this month, but so far, no mold!

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