Common garlic does not produce seeds, so it is propagated by planting bulbs (cloves) from the underground head or aerial bulbs from the inflorescence.

An excerpt from the article 20 facts about garlic

Air bulbs grow slower - they usually need two years of cultivation to produce a bulb of the desired size. Bulbs are usually planted in early spring, but they can also be planted in autumn. The one planted in spring is harvested in August or September, and the autumn one - in July. A folk tradition is to plant garlic on the shortest day of the year.