Green and white mold on dry part of onion only. What to do? I purchased a bunch of red onions and then went a week or two without using them.  When I went to use them last night, I discovered that most of them had grown lots of green and white mold.

This is strange to me - I'm used to onions lasting really long.  In fact, the white onions in the same container were a few weeks older and had no mold or rot.  The white onions aren't even moldy in the presence of the super moldy red onions, and neither are the potatoes or garlic in the same container!

The most interesting part, though, is that only the dry outer skin of the red onions are affected.  The fleshier, shiny layers of skin have no mold.


What kind of mold grows so fast on dry onion skins?
Can we save anything in the bin?
Because nothing else is affected, your red onions probably acquired the mold spores before you purchased them. Perhaps they were stored in a humid area that facilitated the rapid growth. 

Hopefully, you didn't store them in the refrigerator. Onions should be stored in a dry area of your kitchen or pantry in a manner that allows for good air circulation. Use a wicker or wire basket rather than than a plastic container.

I see a big red flag in your mentioning storing potatoes in the same container. Potatoes should never be stored in proximity with onions because onions give off a gas which will cause potatoes to spoil. Keep your potatoes in a separate area, preferably dark, and which also permits air to freely circulate.

Regarding what to do with the moldy onions now: wash off the mold and allow the onions to dry, and/or cook with them as soon as possible. After peeling off the outer skins, if the flesh of the onion looks good, with no mold or dark spoiled areas, then I think they'll be safe to use.

If you have too many onions to cook right away and are afraid the mold will progress, slice and/or dice the onions as desired, and blanch them in some boiling water. Then, seal the blanched onions tightly in one or more packages for freezing.