Common Name: Althea (Rose of Sharon)
Scientific Name: Hibiscus syriacus
Order: Malvales
Family: Malvaceae
Description Althea is a deciduous plant. It has a summer flowering period in which it bears pleasing hollyhock flowers well into the fall. This is a vigorous, upright growing deciduous vase-shaped shrub which can be either left to grow in multi-stemmed shape or thinned to a single stem small tree. Leaves are 3-lobed, medium green in color with a coarse texture. From early summer through the fall it bears very showy hollyhock-like-petaled flowers which can be 3” in diameter. Flowers vary in color but are often pink with red centers. A notable white stamen forms in the center of the flower.
Growth Habit Althea is an easy-to-grow shrub. It grows with a height increase of 13-24” per year. The growth rate ranges from slow to moderate, and transplanting is easy.
Hardiness Zone(s) Althea grows in U.S Department of Agriculture plant hardiness zone 5 (UK) but is also able to grow in the zones 5b-9a, as well as higher zones where temperatures are not extreme.
Culture Althea can grow and survive in full sun, partial sun, or even partial shade. It has certain soil tolerances and soils can vary from sand, loam, clay; acidic; occasionally wet; well-drained. It also has a moderate tolerance to drought. It can grow in suitable pH; the range that is tolerated by the althea varies from 3.7-7.3. Prune the althea in late winter or early spring to promote the new growth and maintain larger flower size. Make cuts above a bud on the branch. Remove about one-third of the wood each year, concentrating on older growth. Cut dead or diseased branches will come back to the base of the shrub. There is a very low pruning rate required for the althea to receive. Frequent severe pruning causes the flowers to be bigger, while little to no pruning causes much smaller flowers. The reason for the low pruning requirement is because the plant itself grows so slowly. There is no real specific time that for someone to prune the althea which makes pruning very simple for this plant.
Diseases & Insects Although usually strong and easy to grow, althea can be bothered by aphids which accumulate at the tips of the stems, causing new growth to be misshapen. Aphids may cover the leaves with sticky honeydew. The insects can be dislodged with high pressure water sprays from the garden hose or controlled by pinching off the part of the twig with the insects. Over-fertilizing increases aphid infestations. Canker is a disease that can kill branches or entire plants. Bright, reddish- orange fruiting bodies may appear on the bark. Need to prune out infected branches. Flowers may be infected with a blight caused by a fungus. Bud drop can be caused by too much or too little water or over fertilization.
Landscape Value Althea is used for many things. It is used for just a container or planter. It is very easy to fit in your house because of the tightness of its structure. It doesn’t take up a whole lot of room at all. It goes beautifully on a deck or patio and is a very fashionable plant. It even has some religious value in it. If enough specimens are available, the owner could use the group of althea as a fence or border between them and the neighboring yard. There are many different colored althea plants available on the market that pose as a beautiful decoration the house or outside where everyone can see. There are many different cultivars that have different colors to each. The colors are as followed red, pink, white, and purple. All of which are very spring and upbeat colors for a person’s yard and can really brighten things up inside of someone’s living area.
References Gilman, E. F. and D. G. Watson. 2014. Hibiscus syriacus: Rose-of-Sharon. University of Florida Institute of Food and Agricultural Sciences. Online.
This document was authored by Kody Brown, Department of Agricultural Sciences, Louisiana Tech University, April 2015.