Dark Mullein prefers well-drained soil and is drought-tolerant once established. Water sparingly, allowing the soil to dry out completely between waterings. Overwatering can lead to root rot.

In very hot, dry climates, occasional deep watering may be beneficial during prolonged dry spells.

Pruning is generally not necessary for Verbascum nigrum. Deadhead spent flower stalks to encourage reblooming and maintain a tidy appearance.

In areas with harsh winters, you can cut back the basal rosette to the ground in late autumn or early spring to promote new growth. Remove any damaged or diseased foliage promptly.

Verbascum nigrum can be propagated by seeds sown in spring or autumn. Seeds may require a period of cold stratification. It can also be propagated by division of the rootstock in early spring.

Cuttings can be taken from basal shoots in spring. This plant often self-seeds readily in favorable conditions.

Repotting is typically only necessary for container-grown plants. Verbascum nigrum prefers to be slightly root-bound and does not require frequent repotting.

If repotting is needed, do so in early spring before new growth emerges. Use a well-draining potting mix and select a pot that is only slightly larger than the current one.