one but usually midwinter in response to an unseasonal warm spell.
The flowers usually keel over immediately and it rarely survives to
repeat the performance the next year! Why does it do better for you?
Well at a guess you have a more consistent cold winter. This is a
plant that flowers near melting snow in the wild, such plants are
often difficult to please in relatively mild lowland gardens.

Crocus goulimyi and Crocus sativus. Both of these thrive under glass
here, Crocus goulimyi increasing quite fast. However Crocus sativus
rarely flowers in the open garden, it simply is not hot and dry enough
in summer. Crocus goulimyi grows OK in the open but only increases
slowly if at all. Again it is likely that it needs warmth and
probably does not appreciate a really cold winter.