Hardy Hibiscus! Mighty Mallow!
Although there are hundreds of hibiscus species, only a few dozen are cold hardy here in the southern US. Here at Plant Delights Nursery, we grow several species of hardy hibiscus plants that fall into two groups: 1) the giant-flowered, dieback species known as Scarlet Rose Mallow or Swamp Rose Mallow and 2) the woody species known as Rose of Sharon or Confederate Rose. Both groups are super easy to grow and provide many weeks of beautiful summer or fall flowers.
Below are the top growing tips for group 1: Rose Mallow and Swamp Rose Mallow. This group includes the species Hibiscus moscheutos, H. coccineus, H. aculeatus, H. dasycalyx, H. lasiocarpos, H. laevis, and H. grandiflorus. Stay tuned for a separate growing guide for Rose of Sharon.
Tip #1 The Importance of Hibiscus Cultivar Selection
Newer hybrids of hardy hibiscus plants (since the 1950's) tend to have fuller petals, larger flowers and a shorter, more garden friendly height. Great cultivars include 'Peppermint Flare', a white with pink splotches, 'Fantasia', a nice pink, and 'Fireball', a great red. All are shorter than wild type plants. Many popular breeding breakthroughs in this group (i.e., purple foliage) were made by the late Fleming brothers of Nebraska and we are pleased to offer many Fleming brother's introductions. We also carry the latest generation of modern hybrids from the breeders at Walter's Gardens. For large gardens, the 8' tall wild type species (i.e., Hibiscus coccineus) look great and their narrow 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. 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 tolerate 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. Leave the dead stems and seed pods until late winter (unless re-seeding is a problem in your garden) as the stems look nice during the winter when covered in frost and snow and the seeds are a winter food source for birds. In spring prune the old stems to the ground as the new shoots emerge. Some folks like to tip prune the new stems in early summer to promote a bushier habit, but Hibiscus will grow just fine without this treatment.
Tip #6 Fertilizer
Rose Mallows and Swamp Mallows respond well to 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. They may drop their flower buds or become susceptible to insects and disease if they are 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 if taken prior to flowering.
Tip #9 Dealing with problems
Rose Mallow and Swamp rose hibiscus may be dined upon by aphids, whiteflies and Japanese beetles. Pest problems are worse if the plant is stressed but pests are easy to control with common organic insect controls. Just be careful not to kill off butterflies or other good insects that may be nearby. Fungus problems can be controlled by maintaining good air circulation around the plant, by keeping mulch from touching the stems, and by 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 so they aren't a good cut flower plant. But the dried seed pods are exotic-looking and will last a long time in an 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 useful 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