Although there are hundreds of species of hibiscus around the world, only few dozen are cold hardy and here in the eastern half of the US, we commonly grow two groups of hardy hibiscus plants 1) the giant-flowered, dieback perennial, Rose Mallow or Swamp Rose and 2) the woody, Rose of Sharon and Confederate Rose.
Both types of hibiscus are super easy to grow and provide weeks to months of beautiful summer flowers. Below are the top growing tips for the Rose Mallow and Swamp Rose hardy hibiscus plants (Hibiscus moscheutos, Hibiscus coccineus, Hibiscus aculeatus, Hibiscus dasycalyx, Hibiscus lasiocarpos, Hibiscus laevis, and Hibiscus grandiflorus).
Tip #1 The Importance of Hibiscus Cultivar Selection
Newer hybrids (since the 1950's) of hardy hibiscus plants tend to have fuller petals, larger flowers and a shorter height. Great modern rose mallow cultivars include 'Peppermint Flare', a white with pink splotches,'Fantasia', a nice pink and 'Fireball', a great red and all are shorter than average. Breeding breakthroughs like hardy hibiscus with purple foliage were made by the late Fleming brothers of Nebraska. We are pleased to offer many of their introductions as well as the next generation of hybrids from the breeders at Walter's Gardens. But for big gardens, the 8' tall wild type Perennial Hibiscus species (like Hibiscus coccineus) look great and their narrower petals are quite beautiful and exotic.
Tip #2 Sun
All hardy hibiscus plants prefer full sun or maybe just a little afternoon shade. More sun = more flowers.
Tip #3 Temperature
Most Hibiscus plants are cold hardy down to zone 4, 5 or 6 depending on the parentage of the cultivar. And at the hot end, they perform well in zone 9 or 10. Click here for a complete list of hardy hibiscus cultivars at Plant Delights to see the hardiness zone range for each.
Tip #4 Soil
Rose Mallow and Swamp Mallow tolerates a wide range of soil types, sand or clay, acid or sweet. Perennial Hibiscus plants are mostly native to swampy areas and can be grown in wet soil along the edge of a pond, but they are also very adaptable and grow well in standard garden conditions.
Tip #5 Pruning
Rose Mallows and Swamp Mallows need little pruning. Unless re-seeding is a problem for you, you should leave the dead stems and seed pods as bird food until late winter as they also look nice in the winter when covered in frost and snow. In late winter or early spring prune your Perennial Hibiscus to the ground. Some folks like to tip prune the new stems when they appear in June or July to promote a bushier habit, but Perennial Hibiscus will grow just fine without this treatment.
Tip #6 Fertilizer
Rose Mallows and Swamp Mallows respond well to medium amounts of organic fertilizer. A fresh topping of compost once a year will suffice.
Tip #7 Watering
Keep Perennial Hibiscus plants well-watered as they do not tolerate drought well and may drop their buds and become susceptible to insects and disease if water stressed.
Tip #8 Propagation
Hardy Hibiscus plants can be divided in spring or you can collect and plant the seed...just note that the seedlings may not resemble the parents. Stem cuttings will root easily prior to flowering.
Tip #9 Dealing with problems
Rose Mallow and Swamp rose hibiscus can be dined on by aphids, whiteflies and Japanese beetles. All are brought on by plant stress but are easy to control with common organic insect controls available at garden centers. Just be careful not to kill off the good insects like butterflies which are attracted to the flowers. Fungus problems can be controlled by maintaining air circulation around the plant, keeping mulch from touching the stems, and removing diseased leaves and discarding them in the trash.
Tip #10 Cut flowers
The giant crepe-papery flowers of the Rose Mallow and Swamp Mallow hibiscus look great but last only a short time in a vase before wilting so they aren't a good cut flower plant. But the dried seed pods are exotic and will last a while in a dried arrangement.
Tip #11 Culinary uses
As a general rule, all perennial hibiscus species are edible...young leaves and flowers have a mild flavor. The leaves, roots, and shoots are filled with a gooey substance (they are mallows - okra relatives) that is used to thicken soups and can even be whipped into a merengue. As the leaves, roots, and stems mature, they become fibrous and unpleasant. Seeds can be pressed to release oil to use in cooking. Try the leaves raw in a salad or boiled like greens, or chopped up and added to soups.
Summer flower fest
The hibiscus smiles full face,
Sensing she’s the best.
~ Gerard Winslow
We hope you find these growing tips useful in growing your Hardy Hibiscus. You can shop for hardy hibiscus at Plant Delights if you want to discover some great new hybrids or some tall wild species. If you have any other hibiscus questions, please contact us at firstname.lastname@example.org and we will have one of our trained staff horticulturists respond.