Althea shrub (Hibiscus syriacus) bears many blooms, and its attractive flowers are its main selling point. As with other types of hibiscus, its flowers bear a striking stamen. Another feature giving the shrub value is its relatively late period of blooming (in many northern climates, it blooms in August). Althea shrub is thus able to offer white, red, lavender, or light blue blooms when many flowering shrubs have long since ceased blooming. Late-summer flowering shrubs can help gardeners manage the sequence of bloom in their landscapes.
Althea shrub is classified by botanists as a shrub, but it can be pruned to form one main trunk so that it grows more like a tree. It can also be used for espalier. Its natural shrub form is multi-stemmed and vase-shaped. It has toothed green leaves that do not provide fall color. It can grow up to 24 inches each year and can be planted in spring or fall.
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|Botanical Name||Hibiscus syriacus|
|Common Name||Althea shrub, Korean rose, rose mallow, Chinese hibiscus|
|Mature Size||8-12 ft. tall, 6-10 ft. wide|
|Sun Exposure||Full sun to part shade|
|Soil pH||Neutral to acidic, alkaline|
|Bloom Time||Late summer, early fall|
|Flower Color||White, red, lavender, light blue|
|Hardiness Zones||5 to 9 (USDA)|
|Native Area||China, India|
Althea Shrub Care
Althea shrub is tolerant of air pollution, heat, humidity, poor soil, and drought. This species has naturalized well in many areas and can become invasive if its growth is not monitored.
This shrub is primarily used as a specimen plant, hedge plant, and foundation shrub. Its attractive and plentiful blooms make it fully capable of holding its own as a specimen. The ability to shape Althea shrub also makes the shrub a prime candidate for hedges. But since this bush is deciduous, it is an effective privacy hedge only in summer (select one of the evergreen shrubs to gain privacy all year).
Althea shrub prefers full sun. Older bushes may fall prey to fungal damage if they are grown in shaded areas where moisture is likely to be high.
This plant thrives in rich soil. It can tolerate many soil types, including sand, clay, chalk, and loam. It prefers nutrient-rich soil but can survive in poor soil, too. Althea shrub thrives in a wide range of soil pH from 5.5 to 7.5.
The plant is reasonably drought-tolerant. In fact, if your Althea shrub has yellow leaves, it could be due to overwatering, rather than to a lack of water.
Temperature and Humidity
A heat lover, this shrub is also prized by growers in the southeastern U.S. who seek plants that can stand up to summer's heat. It is also tolerant of a wide range of humidity conditions.
Fertilizer is recommended (although not mandatory for established shrubs). Use a slow-release fertilizer for shrubs and trees, feeding in late winter or early spring. If you wish to grow organically, work compost gently into the soil around the root zone and water it into the earth.
Althea Shrub Varieties
Althea shrub can be found in a number of different colors. These are some popular varieties:
- 'Blue Chiffon': This cultivar has double flowers with a purple-blue tinge (they're not really blue) that bloom from mid-summer into autumn. What makes the flower so beautiful is the presence of inner petals that surround the stamen, giving the flowers a frilly look. It grows 8 to 12 feet tall, with a spread of 6 to 10 feet.
- 'Sugar Tip': The name of this cultivar refers to its variegated leaves with creamy-white edging. It has pink double flowers and grows six to eight feet tall and four to six feet wide.
- 'White Chiffon': This variety is graced with white flowers that are solid: they have no distinct center, or throat, because the petal is totally white. The shrub grows 6 to 8 feet tall and 4 to 6 feet wide.
- 'Red Heart': This shrub's flowers are ruffled and have a bicolored look with white petals and dark red centers. Lovers of low-maintenance landscaping will be glad to hear that this is a sterile cultivar, so there will not be any seedlings to remove.
Propagating Althea Shrub
The best way to propagate Althea shrub plants is by making stem cuttings and potting them.
- Cut several pencil-wide branches of Althea shrub that have several leaves or leaf buds. Cut the stems 4 to 6 inches long and remove the leaves from the bottom half of the stem.
- Dip the end of the stem in rooting hormone. Plant the bottom third or bottom half of each stem.
- Place a piece of clear plastic over the top of each pot. Water well.
- Put your pots in a spot with shade or indirect light. Remove the plastic in seven days. Check the pots every few days to make sure the potting mixture remains moist. Add more water if needed, but do not let the soil get soggy.
- Check the cuttings for roots in one to two months. Pull gently on each stem; if it resists, the stem has rooted. You also should also see new leaves form on the branch stems that have rooted.
- Grow them larger, at least 2 inches of growth, before planting them in the garden.
Although naturally a multi-stemmed shrub, this plant can be trained through pruning to have just one main trunk; thus, some people refer to it as the Althea shrub "tree." Prune in late winter or early spring, since this is one of the shrubs that blooms on the current season's growth. It is easiest to give Althea shrub its desired shape by pruning it accordingly during its first two seasons. It can also be trained for espalier (grown flat against a supporting structure).
Also, do not give up on Althea shrub, thinking it is dead just because it has not leafed out by early summer. This shrub not only blooms late but leaves out late as well, so be patient.
The chief pest problem for this bush is Japanese beetle infestations. Japanese beetles are somewhat easier to control than many other insect pests because they are large enough to spot immediately before they have done too much damage to your plants. The easiest and safest way to kill them is to pick or shake them off by hand, dropping them into a container filled with soapy water. The insect breathes through its skin, so a coating of soap over its body effectively suffocates it.