Troubleshooting
Common Mullein problems — and how to fix them
Common Mullein (Verbascum thapsus) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Mullein moth caterpillar (Cucullia verbasci)
Yellow-and-black caterpillars can defoliate plants rapidly from late spring; hand-pick and destroy caterpillars or use a biological insecticide such as Bacillus thuringiensis (Bt).
Crown rot in wet soil
The woolly rosette traps moisture in poorly drained or heavy clay soil, causing the crown to rot; plant exclusively in sharp-draining soil and avoid watering directly into the rosette.
Failure to flower (monocarpic confusion)
Plants that germinate late in the season may delay flowering to a third year; this is normal — the plant flowers once it has accumulated sufficient chilling hours, not simply on a one-year calendar.
Prevent common mullein problems before they start
Most common mullein issues are care-mismatch, not bad luck. Dial in the basics:
Common Mullein problems — FAQ
Why is my common mullein mullein moth caterpillar (cucullia verbasci)?
Yellow-and-black caterpillars can defoliate plants rapidly from late spring; hand-pick and destroy caterpillars or use a biological insecticide such as Bacillus thuringiensis (Bt).
Why is my common mullein crown rot in wet soil?
The woolly rosette traps moisture in poorly drained or heavy clay soil, causing the crown to rot; plant exclusively in sharp-draining soil and avoid watering directly into the rosette.
Why is my common mullein failure to flower (monocarpic confusion)?
Plants that germinate late in the season may delay flowering to a third year; this is normal — the plant flowers once it has accumulated sufficient chilling hours, not simply on a one-year calendar.