2. Dec, 2021

Composting Onions

This morning I found half a dozen onions in our communal composting reception bin. Which has resulted in the following  contribution.


There is advice out there that  the onion family and citrus fruits should not be added to the wormery. It is said that they may increase the acidity of the decomposing materials and as high acidity levels will kill the worms it is better not to add them to small domestic wormeries. However, many composters do add onions, shallots, leeks, and garlic to their wormeries either  cooked or in small amounts and  find that   feeding  these  materials in moderation  does not cause problems.

I use two 5 litre caddies to collect kitchen  waste , one for  uncooked kitchen waste,  for the wormeries,  and a second for onion, garlic, citrus, and cooked food which is composted. The   onion and  garlic are put into this  second caddy which is  taken  to the “cooked food”  compost bin or is added directly to a Bokashi bin.to avoid odours in the house.  Onion and cooked waste added to the compost bin is buried, again to reduce odours, which might attract vermin.   

I have relatively small domestic wormeries but many of those with larger scale wormeries who add onion is small amounts have not reported problems although  the worms may be slow to eat the dry outer layer of onion peel

Whole onions added to the bin (as in the photo)  may grow  new shoots but if chopped into small pieces when adding to the bin this should not be a problem. I often  to use  a layer  of shredded paper immediately above the layer containing the chopped onions or onion peel  as I once read that this helps absorbs  the smell ( and I tend to have lots available). Mouldy onions from the kitchen can be composted but it is best not to compost diseased onions from the garden unless you are sure you bin will reached and stay in the thermophilic temperature range.