The hardy perennial hibiscus, also called rose mallow or swamp rose, adds the beauty of a tropical hibiscus to the garden, but can withstand cold winter temperatures that kill the actual tropical varieties.
Perennial hibiscus have big, disc-shaped, hollyhock-like flowers that can be 6 to 12 inches across. The perennial hibiscus species found in gardens are the result of hybridizing native hibiscus species, including Hibiscus moscheutos and H. coccineus.
The larger, more shrub-like hardy hibiscus species, H. syriacus (aka Rose of Sharon), has similar planting and care to the smaller species highlighted in this article. It produces an abundance of smaller flowers and grows into a much larger shrub that doesn’t die back to the ground in winter.
Plants can be purchased from nurseries or started from seed.
Seeds can be sown indoors 12 weeks before the last spring frost. See local frost dates.
Soak seeds in warm water for one hour before sowing.
Seeds can also be sown outdoors after the last expected frost date.
Plant the hibiscus where it is not exposed to strong winds to avoid breakage of the long stems.
Space plants 2 to 3 feet apart.
Mature plants can be divided in the spring.
Mulch around the plant to retain moisture and to provide protection for the roots.
Water plants deeply and thoroughly.
To encourage re-bloom, remove old flowers before they form seed heads or prune plants back by one third after a flush of bloom is finished.
In early spring, remove dead stems from established plants and apply a balanced fertilizer.
Scarlet Swamp Hibiscus (H. coccineus): This plant, also known as Texas Star, has 5-petaled, brilliant-red flowers.
There are many wonderful hardy hibiscus hybrids available. Here are just a few:
‘Lord Baltimore’: Red flowers.
‘Sweet Caroline’: Pink flowers with dark centers.
‘Blue River II’: Beautiful white flowers.
‘Kopper King’: Huge pink blossoms with red centers. It’s named for its dramatic copper-colored foliage.