Common mullein, also known as wooly mullein, is an erect herb.  First year mullein plants are low-growing rosettes of bluish gray-green, feltlike leaves that range from 4-12  inches in length and 1-5 inches in width.  Mature flowering plants are produced the second year, and grow to 5 to 10 feet in height, including the conspicuous flowering stalk.  The five-petaled yellow flowers are arranged in a leafy spike and bloom a few at a time from June-August.  Leaves alternate along the flowering stalks and are much larger toward the base of the plant.  The tiny seeds are pitted and rough with wavy ridges and deep grooves and can germinate after lying dormant in the soil for several decades.

Common mullein threatens natural meadows and forest openings, where it adapts easily to a wide variety of site conditions.  Once established, it grows more vigorously than many native herbs and shrubs, and its growth can overtake a site in fairly short order.  Common mullein is a prolific seeder and its seeds last a very long time in the soil.  An established population of common mullein can be extremely difficult to eradicate.

Common mullein can be found where mean annual precipitation is greater than 3-6 inches and the growing season lasts for a minimum of 140 days.  Intolerant of shade, mullein will grow in almost any open area including natural meadows and forest openings as well as neglected pastures, road cuts, industrial areas.  Common mullein prefers, but is not limited to, dry sandy soils.

During the first summer after germination mullein produces a tap root and a rosette of leaves.   During this vegetative stage, the rosette increases in size during the growing season until low temperatures arrest growth sometime during the autumn and winter.  Beginning the next spring, second year plants bolt into maturity, flower, produce seed during the summer, and then die, completing the plant’s normal life cycle.  Flowers mature from the base to the tip of the stalk.  The length of the flowering period is a function of stalk height; longer stalks can continue to flower into early October.  It is estimated that a single plant can produce 100,000-180,000 seeds which may remain viable for more than 100 years. The seeds are dispersed mechanically near the parent plant during the autumn and winter.  Seeds at or near the surface are more likely to germinate.