Are you looking to add some tropical vibes to your garden? If so, you might be thinking about planting hibiscus. No flower says “tropical” more than the regal hibiscus.
With their large, brightly colored blooms, hibiscus is undeniably showy and add instant aesthetic appeal to a landscape. However, if you live in a northern location, you might think that you’re out of luck, as hibiscus thrive in locations where the weather is warm year-round, such as the tropics and the southern United States.
If you’re a gardener who lives in a northern climate, you’re in luck, because there’s another variety of hibiscus that you can successfully grow: the hardy hibiscus.
Over the past 100 or so years, the hardy hibiscus has become quite popular among gardeners in northern locations.
If you’re interested in adding a touch of the tropics to your landscape, read on to learn more about the hardy hibiscus, including growing tips that can help to ensure the success of these showy plants.
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Hardy Hibiscus: An Overview
The name “hardy hibiscus” is blanket term that is used to describe a couple of different species, as well as their hybrids, all of which are a member of the rose mallow group of the Malvaceae family; the same family as the standard tropical hibiscus.
Unlike their tropical relatives, which thrive in warm temperate, tropical and subtropical locations, hardy hibiscus, as the name suggests, are cold-hardy.
There are a few dozen species of hardy hibiscus, and all of them produce large, eye-catching, showy blooms that can reach as large as 1 foot across (though the averages size is usually 10 inches,) making them the largest perennial flowers in North America.
However, it should be noted that the genetic makeup of individual species, cultivar, or hybrid, the flowers the plants produce can be much smaller in size.
Not only can the size of hardy hibiscus flowers vary, so can he color. Hues include vibrant red, white with hints of light pink, purple, and even blue.
Regardless of the color or size, hardy hibiscus flowers usually feature burgundy- or red-colored throats. They can also feature streaks in a variety of colors that span to the edges of the blooms. Additionally, they also have a prominent pollen-covered staminal column in the center, a hallmark of all types of hibiscus.
Hardy hibiscus can reach anywhere from 2 to 10 feet, depending on the variety. In warmer northern locations, all varieties start to bloom as early as June, but in cooler regions, blooms may not emerge until August and will continue to do so until the first frost arrives.
According to plant taxonomy, hardy hibiscus plants are classified as Hibiscus moscheutos; however, they’re more commonly known as ‘swamp mallows’ and ‘rose mallows.
During the summer season, all varieties have a woody appearance and serve as sub-shrubs; however, in the winter, the stems of the plant die back to the ground, so they’re technically a herbaceous perennial.
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- SOIL WATER & CLIMATE REQUIREMENTS: Choose a site with full sun (at least 6 hours of direct sunlight per day), somewhat protected from the wind, rich soil high in organic matter when possible, and soil that is naturally moist or easily watered on a frequent basis.
- WHEN & HOW TO PLANT: Sow seed indoors 6-12 weeks before the last frost depending on your zone. Sow the large seed ½ inch deep into well-draining soil and keep at 60% humidity in full sun or under lamps. After 4-5 weeks, transplant into larger pots, taking care not to disrupt the taproot.
- COLOR & CHARACTERISTICS: Rose mallow boasts huge, vibrantly colored flowers, some growing to the size of dinner plates. Can grow to be 3 to 8 feet tall and 2 to 5 feet wide.
- GERMINATION & BLOOM: Seedlings emerge in 14-21 days. Soak seeds in room temperature water for about 8 hours to speed germination. Dinner plate hibiscus typically flowers from July-September.
- PLANTING SUGGESTIONS: Particularly vulnerable to beetles and sawflies, but is easy to control by maintaining good air circulation around the plant and by removing diseased leaves. Can combination with spring bloomers such as creeping phlox or Jacob's Ladder.
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History of Hardy Hibiscus
Hardy hibiscus have existed for about 100 years, when breeders of plants started to work on developing hybrids of the tropical variety that could tolerate colder temperatures.
According to Gretchen Zwetzig, the owner of Fleming Flower, one of the oldest flower breeding companies, breeding of the cold-hardy varieties really only started to become commonplace in the 1950s.
Robert Darby is credited with being one of the first modern cultivators of hardy hibiscus. He successfully developed two of the first successful hybrids, Lady Baltimore and Lord Baltimore, by cross-breeding at least four native species of hibiscus, including H. militaris (now known as H. laevvis), H. palustris, H. coccineus, and Hibiscus moscheutos. Lady and Lord Baltimore remain popular hardy hibiscus flowers.
In the 1960s, Sakata Seed Corporation started to hybridize hardy hibiscus in Japan and they successfully established the H. Dixie Belle and the H. Southern Belle varieties. They also cross-bred the Disco Belle series in the 1970s.
Fleming Flower, a Nebraska-based company, also worked on hybridizing the flowers. They successfully produced several varieties of hardy hibiscus, including the Kopper King, Old Yella, Fireball, Torchy, Dream Catcher, Fantasia, Plum Crazy, and Robert Fleming.
Hardy Hibiscus Planting and Care Requirements
In order to successfully plant hardy hibiscus, you need to make sure that you plant and care for these flowers properly.
In this section of our guide, we share some important tips that will help to ensure your northern garden has a touch of the tropics with the show blooms of these herbaceous perennials.
Seed Planting
- If you are planting hardy hibiscus from seeds indoors, the best time to do so is three months before the last average frost date in Zone 6 or lower.
- If you are located in zone 7 or a warmer location, you can begin your seeds indoors one to two months before the last average frost date, or you can sow the seeds directly in the soil after the risk of frost has passed.
- Whether you’re planting them indoors or out, make sure to soak your seeds overnight before planting.
- Set the soaked seeds about ½ inch deep into the soil. If planting indoors, start to harden the plants off as the last frost date arrives in order to expose them to outdoor conditions, including sunlight and wind, when the weather is favorable.
- On the first day, bring them outdoors for about 30 minutes and increase the amount of time they’re outside by about 1 hour each day for five more days before you transplant them into your garden.
Choosing and Preparing a Location
- Hardy hibiscus do best in medium to wet soil that drains well. The soil shouldn’t be too heavy; however, these plants will not do well in sandy, dry, or poor-draining soils.
- Therefore, if the soil in your garden is sandy or drains poorly, mix in a few inches of organic compost before planting your flowers.
- In cooler climates (zones 4 to 6), hardy hibiscus will do best when planted near south-facing wall, where they will receive plenty of sunlight and are protected from wind.
- If you live in a warmer climate, a location that receives about 6 hours of sun a day would be ideal; however, do note that if they receive too much shade, their stems will likely be long and leggy and their blooms may not be as healthy or they may not produce any blooms at all.
Watering
In the wild, hardy hibiscus grows in swamp areas. While cross-breeding has reduced the water requirements for many varieties, they do still need to receive adequate water in order to thrive.
Make sure that the soil remains moist; however, you don’t want to water the plant too much, as doing so could lead to root rot.
Smaller plants with less leaves don’t need to be watered as often as larger, leafier plants. During the growing season, hardy hibiscus should be watered on a daily basis.
Feeding Requirements
Hibiscus plants need a lot of nutrients when they are growing. To ensure that your plants receive the nutrition that they need, we recommend feeding them with a water-soluble or slow-release fertilizer; however, take care to ensure that the nutrients are well-balanced, as over-fertilizing can lead to toxicity, which can result in imbalances and severely damage or even kill the plant.
A 10-10-10 or a 20-20-20 fertilizer will yield the best results. Alternatively, you can feed your plants with a diluted liquid fertilizer on a weekly basis, or apply a slow-release fertilizer to the soil four times per year: once in the early spring once after the first round of blooms expires, mid-summer, and early winter.
Pruning
Because the hardy hibiscus is a herbaceous perennial, it dies back to the ground during the winter. Therefore, you can prune the plant to the ground during the fall season, even though the branches may still appear to be healthy.
Cold Weather Care
If you live in a location where the temperatures fall to below freezing during the winter season, you’ll need to protect your hardy hibiscus to ensure they survive.
To do so, apply about 3 to 4 inches of fresh mulch after you’ve pruned the flowers back to protect the roots from the frigid temperatures. Wood chips, leaves, or straw can all be used to shield the roots from the cold.
If properly protected, hardy hibiscus will regrow in the spring. However, do be patient, as these plants are later risers. They usually send out their first signs of new growth in May or June (depending on the climate in your area).
Pests and Diseases
Hardy hibiscus can have issues with pests and disease.
In terms of pests, deer like to munch on these plants. To keep them away, place fencing around your hardy hibiscus. Aphids can also be a problem, as they eat away at the leaves, the stems, and the flowers. Apply an insecticidal soap to the infected plants on a weekly basis.
Hardy hibiscus can develop fungal infections, including rust, leaf spot, and botrytis blight. To prevent disease, avoid getting the leaves wet when watering.
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