Great mullein is a biennial and generally requires winter dormancy before it can flower. This dormancy is linked to starch degradation activated by low temperatures in the root, and gibberellin application bypasses this requirement. Seeds germinate almost solely in bare soil, at temperatures between 10 °C and 40 °C. While they can germinate in total darkness if proper conditions are present (tests give a 35% germination rate under ideal conditions), in the wild, they in practice only do so when exposed to light, or very close to the soil surface, which explains the plant's habitat preferences. While it can also grow in areas where some vegetation already exists, growth of the rosettes on bare soil is four to seven times more rapid.