Vernalization: In some species, flowers are formed in spring as a result of the plant […] being given a cold treatment, close to or at freezing temperatures, for several weeks. The physiological process is called vernalization (from Latin for “belonging to spring”).*
Spring bulbs, like these Allium christophii, require a vernalization period in the ground over winter. That’s why they’re planted in autumn.
*Capon, B. (2005). Botany for gardeners (Revised ed). Portland: Timber Press.