Verbascum plants are more commonly called mullein and are typically perennials, though they do not live for many years. They are hardy plants that thrive even in poor soils. The plants develop tall, vertical stalks with green foliage and produce large, saucer-shaped flowers at the top. The flowers are usually yellow but can also be white, purple or reddish orange. Pruning verbascum plants is done to remove the dead flower blooms and encourage repeat blooming throughout the growing season.
Wait until the verbascum plants produce flower blooms, which typically occurs in late spring or early summer.
Watch the plants daily for signs of the blooms starting to wilt. When the flower on a stem starts to wilt, use hand pruners to cut the entire stalk off as close to the base of the plant as possible. If desired, you can also prune the stalk off near the top just above where a bud is located.
Continue pruning in this manner throughout the growing season to force the plant to grow new stalks and new blooms.
Stop pruning in the fall once a complete new set of verbascum flowers has developed. Allow the flowers to wilt and seed pods to develop. Once the pods open, the seeds will fall to the ground and grow the following year. Prune the dead stalks off near the base once the seed pods open.
If you do not want the verbascum plants to regrow, continue pruning the plant until it dies in the winter.