To propagate mullein, the most common method is to start from seeds by direct sowing outdoors in fall or early spring, as seeds need light to germinate and should be scattered on the soil surface without covering them; you can also start seeds indoors 6-8 weeks before the last frost, but be sure to cold stratify the seeds beforehand by keeping them in the fridge for a few weeks;.
Key points about propagating mullein:
Seed propagation: This is the preferred method as mullein readily self-seeds.
Direct sowing: Scatter seeds directly on the soil surface in a location with full sun.
Light requirement: Mullein seeds need light to germinate, so do not bury them deep.
Cold stratification: If starting seeds indoors, consider cold stratification by keeping them in the refrigerator for a few weeks before planting.
Harvesting seeds: Collect seeds from the dried flower stalks after blooming.
Other less common methods (with limitations):
Root cuttings: You can try taking root cuttings during the plant’s dormant period in late fall or early spring.
Stem cuttings: Though less reliable, some gardeners attempt to propagate mullein using stem cuttings with rooting hormone.