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Make sure to let the foliage die back. This means don't uproot the corms after the blooms fade. This could sacrifice your blooms for next season.
Use a small garden fork to dig up the corm. A shovel could cut through them.
Allow the corm to dry out for a few days and then you can clean off the excess soil. I don't prefer using water; because, corms rot easily and I like to avoid extra moisture.
Trim off the dead foliage and use a dry toothbrush to clean off any remaining dirt. Your corm will be ready to be stored when you have an ugly dried up octopus shaped item in front of you.
Corms need to stay cool and dry. If moisture is a problem try adding silica packets to your contained to keep them dry.
Do not store too many corms together to avoid moisture causing rot. I stored mine in paper bags.
Make sure to get rid of any problematic corms that might be causing rot.