Water moderately during its establishment phase, especially in its first year. Once established, Dense-flowered Mullein is quite drought-tolerant and prefers well-drained soil.

Allow the soil to dry out between waterings to prevent root rot. Reduce watering in winter.

Deadheading spent flower spikes can encourage a longer blooming period and prevent self-seeding if unwanted. After flowering, you can cut back the main flower stalk to the basal rosette.

Remove any dead or damaged foliage in late winter or early spring.

Dense-flowered Mullein is easily propagated by seeds sown directly outdoors in autumn or early spring. Seeds can also be started indoors a few weeks before the last frost. It readily self-seeds in suitable conditions.

Division of established clumps is also possible.

As this is typically a biennial or short-lived perennial grown for its dramatic flower spikes, frequent repotting is generally not necessary. If growing in containers, repot only when the plant becomes root-bound, typically every 1-2 years, using well-draining potting mix.