I love onions and it's always cheaper to buy in large quantities but that can lead to spoilage, especially where I live, on the West Coast where it is quite humid. I've tried various methods before and they haven't worked that well.
Just recently a 50lb bag of onions was one third the regular price at a store near here and the deal was so good that I bought some. Problem is that I can't eat that much before they go bad sooooo I'm trying an experiment. I got the idea from here: https://jeromestueart.com/2009/09/13/how-to-keep-...
In the comments on the page quite a few people asked if this could be done with onions but there didn't seem to be a reply. It might work because moisture is a problem with onions going bad and the peat moss should regulate that. Whether this works or not is to be seen and I'll update this instructable with the results. The onions were cheap enough that if it doesn't work it won't be so bad.
UPDATE: Didn't work so well. After about five months I had to discard about half of them. It works for the first three months but after that they start to go soft.
Step 1: What You Need
-1 cubic ft of peat moss
-two weak garbage bags or one strong one
-tube from an old pen
Step 2: What to Do
First, empty out the onion bag and then put it inside the garbage bag(s). Reuse the onion bag because it's strong and the mesh might allow for more air circulation, keeping the onions away from the plastic. Then put a layer of peat moss on the bottom, then a layer of onions, a layer of peat moss, a layer of onions, etc., until the final layer of onions is covered in peat moss. Close up the onion bag and use the tube from an old pen and a twist tie to close the garbage bags. The tube allows air into the bags so the peat moss can breathe. Then put whole thing into a dark, cool place.
Only half a cubic foot of compressed peat moss was used for the 50 lb bag of onions. Hopefully this works. If not then it goes into the compost. Fortunately there's enough peat moss left over to experiment with other vegetables.
You could also try this with sand. Please let me know if you have any experience with this.