Introduction
The hibiscus is more than just a pretty tropical flower. It’s Hawaii’s state flower, South Korea’s national flower, and a worldwide symbol of love, admiration, and strength. This incredibly diverse plant has become a favorite for many gardeners across the globe. These sizable tropical blooms come in colors that span nearly the entire rainbow. This care guide will provide information on well-known varieties of hibiscus, tips on planting and growing hibiscus, and how to deal with problems that commonly impact the health of these plants.
Understanding Hibiscus Shrubs
Like most plant genus, there are many, many varieties of hibiscus. Below we’ll cover the ones that are commonly sold and grown throughout the U.S.
Tropical Hibiscus (Hibiscus rosa sinensis) - Perhaps the most recognizable of the varieties, tropical hibiscus plants are also called Chinese hibiscus or China rose. The variety is thought to have originated from tropical regions in Asia. It has been widely cultivated across the globe for centuries.
This hibiscus has a shrub-like habit, but can be grafted or trained to create a hibiscus tree form. It thrives in warm, humid conditions and does not tolerate temperatures below 55 degrees. Like most tropical plants, they are usually only grown outdoors year-round in places like Hawaii and southern Florida, in growing zones 10-12. They can be grown in containers in northern states, and kept inside when nighttime temperatures fall below 55. This is typically called overwintering; see more details below. If you’re unsure what growing zone you’re in, check out this interactive map!
The colorful flowers on the tropical hibiscus can grow between 4-6” and only bloom for a day or two before wilting. But, they are heavy bloomers, meaning there are always more blossoms around the corner during the growing season! If planted in the ground they can grow up to 10’ tall by 5’ wide, making them great hedges or screens.
Shrub Hibiscus (Hibiscus syriacus) - This hardy hibiscus is also known as Rose of Sharon or Althea. These hibiscus plants are native to central and southern Asia. Varieties tend to have a greater number of flowers than the tropical hibiscus, and a much wider range, typically between zones 5-9. Unlike tropical hibiscus, the shrub hibiscus doesn’t bloom with colors like yellows or oranges. Pinks, whites, and even shades of violet are more common. For the best flowering, plant in full sun. Pollinators love this hibiscus plant!
Our nursery has several varieties of bare root Rose of Sharon to choose from. These hardy hibiscus can be shipped across the U.S.
Perennial Hibiscus (Hibiscus moscheutos and Hibiscus coccineaus) - The last type of popular hibiscus is the perennial hibiscus, also known as rose mallow. These hardy hibiscus are native to the U.S. in swamp-like conditions from Florida to most of the southeast.
Perennial hibiscus have numerous large blooms, which last from midsummer to the first frost. They thrive between zones 5-9. As a perennial, they will die back in winter, and push new growth in spring. Though they emerge later in the season than most perennials, these hibiscus are quick growers, and can grow as much as an inch per day!
Planting Your Hibiscus
For all types of hibiscus, plant in spring or fall when there is no risk for frost. This will give your hibiscus the best chance to survive. We recommend fall for its cooler temperatures, increased moisture in the soil, and reduced disease and pest opportunity. Plant hibiscus in full sun, and if you’re in a hot climate, plant it in an area that’s protected from afternoon sun.
Tropical and shrub hibiscus prefer a slightly acidic, well-drained soil mixture, rich with organic matter. Perennial hibiscus, being native to swampy areas, prefers well-drained, evenly moist, humus-rich soil.
After planting your hibiscus, make sure to water the plant properly. Healthy watering practices will go a long way in helping your hibiscus thrive. While we’re on the subject of giving plants their best chance, mulching has many benefits, including: deterring weed growth, maintaining soil moisture, and protecting the soil from erosion.
Fertilizing Hibiscus
In order to sustain their rapid growth during the season, hibiscus flowers benefit greatly from a balanced fertilizer, such as 10-10-10 or 20-20-20. Fertilize every 2-3 weeks in summer, and every month in spring. If the plant is going to be overwintered indoors, you should use a ½ strength fertilizer and reduce the frequency.
Pruning Hibiscus
Depending on your location and the specific variety, different methods are employed to prune hibiscus. Tropical hibiscus can be pruned in fall if you’re in a climate with no frost risk, or in spring if you’re in a cooler climate. Trim off any leggy old growth to encourage a healthy and compact shape.
Shrub hibiscus doesn’t need to be pruned, but if you’d like to maintain the plant’s shape and encourage a larger hibiscus flower, then trim it back by about 1/3rd in early spring before new growth appears. Remove any leggy or weak branches to encourage healthy growth.
Perennial hibiscus should be heavily pruned in spring after the new growth starts to emerge. Prune the old stems to around 6”. If you’d like a bushier hibiscus, you can trim the tips of the branches in early summer.
Overwintering Hibiscus
While the shrub hibiscus and perennial hibiscus are generally hardy for colder climates, lay a fresh layer of organic mulch around the base of the plant before the first hard frost. This will help regulate the temperature, protecting the hardy hibiscus from the dramatic temperature fluctuations of winter.
Tropical hibiscus, if kept outdoor in zones cooler than 10, can be overwintered indoors. Make sure you place the plant where it will receive at least 2-3 hours of direct sunlight daily, and where temperatures are above 55 degrees F. Once inside, reduce the waterings and fertilization. Remove any buds if you see them; you don’t want the plant to use up energy flowering in winter. Keep the hibiscus indoors until spring, when nighttime temperatures are above 55 degrees.
Common Pests and Problems
The most common pests that may impact a hibiscus are aphids, spider mites, and sawflies. If you notice any signs of these pests, use insecticidal soap like neem oil, or consult a local garden center for treatment.
Besides pests, hibiscus can have issues such as yellowing leaves and bud drop. These could be signs of overwatering, or that the temperature is too warm or cold. For tropical hibiscus, between 65-75 degrees F is the ideal daytime temperature to develop their stunning blooms. These could also be caused by too little sunlight.
Conclusion
The exotic flowers on these beautiful shrubs can grace your yard for years, if proper care is taken with them. We hope the above tips provide you with enough confidence to grow hibiscus in your own garden.
If you have any questions, you can always reach out to us, or if you’re in Wisconsin, visit one of our Garden Centers.