In message , Steve
Harris writes
In article ,
(Stephen Howard) wrote:

diseases that onions are prone to...but then follows standard advice
not to compost diseased material unless you're sure your process will
deal with it.

You might not know the disease organisms were present on bought onions.
If you imported certain onion diseases into your garden, it could take
8 years to get rid of them.

That is the main reason why composting onions is not usually
recommended. The white onion rot spores are tough and will persist for
several years until another host crop is grown.

Regards,
--
Martin Brown