You can leave them in the ground until you use them. They are not so much troubles by slugs as potatoes are.

They don't flower well in this country, and they'll probably be frosted before hey try to set seed. There's so much leaf mass compared with the flower that it won't affect tuber formation noticeably. (Or, to put it another way, given their digestive properties,, you probably won't feel you have a shortage of them).