Water Broad-leaved Hemp-nettle regularly, especially during dry spells, to maintain consistently moist soil. Avoid waterlogging, as this can lead to root rot.

Reduce watering in cooler months when the plant's growth slows down. Check the top inch of soil before watering.

Pruning is usually not necessary for Broad-leaved Hemp-nettle. If plants become leggy or overgrown, light trimming in early spring can help maintain a more compact shape.

Deadheading spent flowers can prevent unwanted self-seeding and encourage a second flush of blooms.

Propagate Galeopsis ladanum by seeds sown directly into the garden in early spring or autumn. Seeds germinate readily and often self-seed prolifically.

Alternatively, cuttings can be taken in late spring or early summer and rooted in moist soil or a propagation medium.

Repotting is typically not required for this species, as it is often grown as an annual or short-lived perennial and tends to self-seed. If grown in containers, repot in spring if root-bound, using a well-draining, general-purpose potting mix.