Hardy Hibiscus: Care and Growing Guide

Hardy hibiscus is a group of several hibiscus perennial shrubs that produce large, tropical-like flowers in shades of red, pink, purple, and white. Hardy hibiscus also has some of the largest flowers of any perennial garden shrubs. For example, the “Dinner Plate” hibiscus (Hibiscus moscheutos) is a cold-hardy shrub with huge, flat circular blooms up to 9” (22 cm) wide.

Most people think of hibiscus flowers as tropical blooms that only grow in warm climates. However, hardy hibiscus grows in USDA zones 4 through 9. So, even if you get below-freezing temperatures during the winter months, hardy hibiscus plants will thrive and bloom in your front or backyard. From the warm, humid climates like Florida to colder regions in northern states, cold-hardy hibiscus can produce spectacular flowers from mid-summer until fall.

This article is a complete care guide to growing perennial hibiscus shrubs suitable for cold climates. You will also learn about the hardy hibiscus cultivars and hybrids that survive in temperatures as low as -30°F (-34°C).

What is Hardy Hibiscus

Hardy hibiscus is a genus of perennial flowering shrubs or small trees in the family Malvaceae. The three main species of hardy hibiscus are rose of Sharon (Hibiscus syriacus), rose mallow (Hibiscus coccineus), and Hibiscus moscheutos, which is also called rose mallow or swamp hibiscus. The versatile perennials bloom with stunning flowers ranging in size from 2” to 9” (5 – 22 cm) across.

Hardy hibiscus is a cold-hardy plant that thrives in freezing conditions in USDA zones 5 to 9. In some areas, hardy hibiscus shrubs survive outdoors in zone 4 with protection by mulching the root zone.

Perennial hibiscus plants are generally large shrubs or small flowering trees. Rose of Sharon is the largest of the hardy hibiscus species, growing between 8 and 12 ft. (2.4 – 3.6 m) tall and 10 ft. (3 m) wide. Rose mallow shrubs are smaller, with a height of 3 to 7 ft. (1 – 2.1 m) and width of 4 ft. (1.2 m).

Apart from the beautiful massive “dinner plate” flowers, hardy hibiscus has attractive foliage. Leaves are lush green, with some species having heart-shaped ovate leaves and others having lobed, palmate leaves.

Varieties of hardy hibiscus differ from tropical hibiscus because they grow in cold climates. Species of tropical hibiscus such as Chinese hibiscus (Hibiscus rosa-sinensis) only grow in USDA zones 10 through 12. Also, tropical hibiscus shrubs tend to grow larger, showier flowers but are more challenging to care for.

How to Care for Hardy Hibiscus

To care for hardy hibiscus, grow the shrub or hibiscus tree in well-draining ground that holds moisture. Water hardy hibiscus plants regularly during hot weather and less in winter. Fertilize hibiscus with a high potassium fertilizer in spring and prune branches in spring before new growth appears. Deadhead hardy hibiscus in the fall.

Hardy Hibiscus Flowers

Hardy hibiscus trees and shrubs bloom with large, round brightly-colored tropical-looking flowers. The funnel-shaped hibiscus flowers open out to create a sizeable plate-like disc with a protruding stamen from the center. The saucer-sized flowers bloom in purple, red, pink, and white colors. Hibiscus perennial flowers sometimes have a contrasting, dark-colored center.

Hardy perennial hibiscus starts blooming in mid- to late-summer. The individual flowers may only bloom for one to three days. However, the large flowering bush will continue blooming for a few weeks until fall.

Varieties of Hardy Hibiscus

Hardy hibiscus perennials come in a range of cultivars and hybrids. Rose of Sharon (Hibiscus syriacus) is the largest of the hardy hibiscus species. Hibiscus moscheutos is a smaller shrub but called “Dinner Plate” hibiscus due to its colossal saucer flowers. Rose mallow (Hibiscus coccineus) is a perennial shrub growing up to 6 ft. (1.8 m) tall.

Hardy hibiscus shrubs can be large, spreading bushy plants or dwarf cultivars for smaller gardens.

Here are some of the most spectacular cold-hardy hibiscus plants for growing in cold climates:

• Hibiscus moscheutos ‘Luna White’—A compact perennial shrub with magnificent, brilliant white saucer flowers with red centers measuring 8” (20 cm) across. The low-growing hardy hibiscus grows between 2 and 3 ft. (0.6 – 1 m) tall.
• Hibiscus coccineus ‘Berry Awesome’—Also called “dinner plate hibiscus,” this deciduous shrub has massive pink disc-like flowers that bloom continuously from mid to late summer. This rose mallow grows 4 ft. (1.2 m) tall and is 5 ft. (1.5 m) wide.
• Hibiscus moscheutos ‘Fireball Hibiscus’—This hardy hibiscus has gigantic red flowers up to 10” (25 cm) across that bloom until late in the season. The hardy ‘Fireball’ hibiscus grows 4 to 6 ft. tall and is 3 ft. (1 m) wide.
• Hibiscus coccineus ‘Midnight Marvel’—A spectacular hardy hibiscus shrub with dark palmate leaves and colossal 9-inch (22-cm) red flowers. The individual blooms last for one day, but the shrub blooms from mid-summer until fall. This hibiscus rose mallow reaches 4 ft. (1.2 m) high.
• Hibiscus syriacus ‘Pink Chiffon’—A bushy hibiscus perennial with stunning ruffled semi-double, light pink flowers that measure 3” (8 cm) across. The hardy shrub grows between 8 and 12 ft. (2.4 – 3.6 cm) high.

Hardy Hibiscus Care

Let’s look in more detail at how to grow hardy hibiscus perennial shrubs to add beauty and greenery to your front or backyard.

Where to Plant Hardy Hibiscus Shrubs

Hardy hibiscus needs around six hours of sunshine daily, so you should plant the shrub in the sunniest part of your garden. Rose of Sharon and rose mallow plants will grow in partial shade. However, hardy hibiscus plants won’t bloom as much if planted in shaded areas of your yard.

It’s vital to protect the plant from too much or too little light to care appropriately for hardy hibiscus shrubs and trees. Intense, direct sunlight on hot summer days can cause leaves to turn yellow. But this is usually only a problem when growing hardy hibiscus in sweltering tropical regions.

If a small hardy hibiscus tree or shrub is in constant shade, you may get problems with powdery mildew.

The Best Soil for Growing Hardy Hibiscus

Hardy hibiscus grows best in moist soil that has good drainage. The best kind of soil should be loose and airy with a fair amount of organic matter such as compost or peat moss. Hibiscus soil needs amending if there is too much clay or the ground is too dry and sandy.

Some hardy hibiscus shrubs are also called swamp hibiscus because they grow in wet soil with medium drainage.

In most cases, the best way to care for rose of Sharon, rose mallows, and swamp hibiscus is to ensure the ground is continuously moist in summer. This way, you will encourage prolific blooming, with a constant supply of large, dinner-plate flowers throughout the summer.

Watering Hardy Hibiscus Plants

Water cold-hardy hibiscus shrubs every week in the summer and twice a week in scorching weather. To care properly for hibiscus, you should water enough so that the ground is evenly moist. You should hold off watering in winter—just water enough so the soil doesn’t completely dry out.

Here are a few handy tips on watering hardy hibiscus plants for best results:

• Never overwater the drought-tolerant shrubs to prevent root rot.
• Prevent the ground around the hibiscus roots from becoming waterlogged.
• Always water the ground and avoid wetting the leaves to prevent powdery mildew.

How to Grow Hibiscus in Pots

Hardy hibiscus plants grow in containers if you have a large enough pot. Grow the dwarf hibiscus shrub in a loose potting soil mix with one-part peat moss and one-part perlite. Water the potting mix regularly to keep the soil slightly moist. Place the potted hibiscus shrubs on your patio, balcony, or deck in the sunniest spot.

If growing hibiscus in pots indoors, protect the plant from intense direct sunlight.

Related reading: How to water tropical houseplants growing indoors.

How to Prune Hardy Hibiscus Bushes

Only prune hardy hibiscus shrubs to remove old growth or cut the shrub back in winter. Hardy hibiscus plants die back every year, and new growth in spring starts from the ground. You can also prune branch tips in early summer to encourage branching and prolific blooming.

How to Fertilize Hardy Hibiscus

Hardy hibiscus trees and shrubs benefit from potassium-rich fertilizer with adequate amounts of nitrogen to boost growth and blooming. Generally, applying a layer of organically-rich compost in spring provides enough nutrients to stimulate vigorous growth. Or a suitable slow-release organic fertilizer can help to keep the hardy hibiscus growing healthy.

If you decide to use a commercial fertilizer, make sure you don’t over-fertilize the plant. Choose a fertilizer with an NPK rating of 10-4-12 or 9-3-13 to ensure the nutrient profile is ideal. Too much phosphorus can inhibit blooming and affect growth.

Hibiscus Propagation

Varieties of hardy hibiscus are easier to propagate than tropical hibiscus plants. The two easiest ways to grow new hibiscus shrubs from the “mother” plant are stem cuttings and from seed.

Let’s look briefly at how to propagate hardy hibiscus.

How to propagate hibiscus from seed

If your hibiscus shrubs produce seeds—remember that not all do—you can collect seeds for germinating. You should make a small cut in the seeds using a sharp knife. Then soak the seeds overnight before planting in a light soil mix. Put in a warm place, cover with plastic, and keep the soil moist. It takes between two and four weeks for seedlings to appear.

How to propagate hibiscus from stem cuttings

The easiest way to propagate hibiscus is by using stem cutting. Cut a 6-inch (15 cm) healthy softwood hibiscus stem in spring and remove the lower leaves. Dip the branch’s end in rooting hormone and place it in a pot with a loose, damp potting mix.

Cover the pot with a plastic bag to increase humidity. Then, place it in a warm location that is at least 60°F (15°C). Keep the potting mix moist. It should take a couple of months for new foliage to grow and roots to appear. Transplant the rooted cutting to a larger container and grow for a season before transferring to a sunny spot in your garden.

Transplanting Hardy Hibiscus Plants

Hardy hibiscus doesn’t respond well to transplanting, so you need to use care when moving it to a new location. The best time to transplant a hardy hibiscus is in early fall after the perennial has finished blooming. Good preparation is key to successfully moving a hibiscus.

First, dig a large hole in the new location. Then, prune back the hibiscus to about one-third of its current size. For the next step, dig around the root zone at a distance of 12” (30 cm) for every 1” (2.5 cm) of trunk. Next, separate the roots from the soil.

Using a wheelbarrow, take the hibiscus to the new location and put it in the hole. Remember, you may have to enlarge the hole if necessary. Ensure that the trunk’s soil line is level with the ground and fill the remaining space with soil from the hole. Firmly press the soil down and thoroughly water the hibiscus.

For the next few weeks, water the newly-transplanted hibiscus every two to three days.

How to Care for Hibiscus in Winter

Hardy perennial hibiscus plants die back in winter and survive severe winter conditions in zones 4 through 9. Prepare the hibiscus for winter by pruning the stems back, so there is just under one foot (30 cm) of stems sticking out above the ground. Put a thick layer of mulch over the root zone to protect the roots from freezing temperatures.

How to Get Rid of Pests that Affect Hardy Hibiscus Plant Growth

Hardy hibiscus plants are easy to grow but are susceptible to pest infestations. Use a neem oil solution spray to eradicate pests from hibiscus plants. Use 2 tsp. neem oil and 1 tsp. liquid Castile soap for every quart (1 l) of water to make a bug spray.

Mix thoroughly in a pump spray bottle and thoroughly soak both sides of the foliage and leave to dry. Use the neem oil pest spray once a week to get rid of pests from hibiscus plants for good.

Common pests affecting hibiscus plants are mealybugs, spider mites, aphids, and whiteflies.

Diseases Affecting Hibiscus Plant Growth

Fungal diseases are the main issues when caring for hardy hibiscus perennial garden plants. Waterlogged ground can create root rot. The signs of hibiscus root rot are flower buds that drop, yellow leaves, and leaf drop. Also, too much moisture around the foliage can cause powdery mildew.

The best way to prevent diseases affecting hardy hibiscus is to water the perennial properly. Water the flowering garden plant weekly in warm weather and only occasionally during winter.

FAQs About Hardy Hibiscus Care

Hardy hibiscus shrubs are generally easy to care for perennials. With little pruning required, you only have to water the shrub in hot weather to keep the ground moist. However, some issues can affect hardy hibiscus growth.

Does Hardy Hibiscus Come Back Every Year?

Cold-hardy hibiscus plants are perennials that come back year after year and bloom continuously from late summer until fall. In cold climates, perennial hibiscus plants die back to the ground in freezing temperatures. You can then prune the stems, so there is about 4” to 5” (10 – 12 cm) sticking up from the ground. Hibiscus will return in late spring.

Why Are My Hibiscus Leaves Turning Yellow and Falling Off?

Watering issues—too much water or not enough—can cause hibiscus leaves to turn yellow. Hardy hibiscus is generally tolerant of drought, but parched ground can starve foliage of nutrients. Also, overwatering or poor drainage can cause root rot and cause yellow hibiscus leaves. Make sure the soil is always moist but never soggy.

How Do I Keep My Hibiscus Blooming?

Water your hardy hibiscus during hot weather to keep the shrub producing flowers throughout the summer. Hibiscus blooms may only last a day or two. But with enough hydration, the flowering shrub will continuously bloom in summer and fall.

Why Are Hibiscus Flower Buds Dropping?

Lack of water is the primary reason hardy hibiscus drops its flower buds and flowers. Although rose of Sharon and rose mallow survive drought well, buds can start dropping if the ground is arid or there is excessive heat. Ensure that you water the perennial hibiscus well during warm summers.

How to Get Rid of Fungus on Hibiscus Plants

Fungus on hibiscus plants is powdery mildew that causes leaves to turn a grayish-white color. Get rid of powdery mildew fungus by spraying the leaves with a diluted milk mixture or a baking soda spray.

To prevent fungus on hibiscus plants, always water the ground, not the leaves. Also, ensure the shrub is growing where there’s enough air circulation for its dense foliage.

Discover the most beautiful types of hibiscus.

Related articles:

• Hibiscus Tree: Care and Growing Guide
• Rose of Sharon (Hibiscus Syriacus): Care & Varieties
• Small or Dwarf Flowering Shrubs