Water regularly to keep the soil consistently moist, especially during dry periods. Avoid waterlogging the roots, as this can lead to root rot. Reduce watering in the fall and winter when the plant's growth slows down.

Prune back dead or damaged stems anytime. To maintain a tidy appearance and encourage bushier growth, cut back the plant by about one-third in late spring or early summer.

Deadheading spent flowers can prevent unwanted self-seeding.

Easily propagated from seed sown in the fall or early spring. Division of established clumps in early spring is also an effective method. Cuttings taken in late spring or early summer can also be rooted successfully.

Ageratina altissima is a vigorous perennial that benefits from division rather than repotting. If a specimen becomes overgrown or congested, divide the root ball in early spring.

Newly divided sections can be replanted directly into the garden.