Althaea

Hibiscus syriacus

The hibiscus-like flowers of althaea figure prominently in many Southerner’s notions of pretty flowers. Thomas Jefferson admired them, as well, and grew many different kinds at Monticello.  

Rose of Sharon or althaea belongs to the mallow family. It grows into a large shrub or small, multitrunked tree that blooms from June through August. Colors range from white to pink, lavender, and reddish purple. Some have a dark colored splotch in the center. Flowers may be single, double, or semidouble. 

Culture 

Althea is very unfussy about soil. Plant in well-drained soil and mulch well to keep moisture from fluctuating. Bloom is best in full sun, but some shade is tolerated. Water newly planted shrubs every few days until they become established, and then water deeply during extended drought. Afterwards you can pretty much sit back and enjoy the show. Pruning is not necessary, but larger flowers will result if shrubs are pruned lightly in the spring. 

Altheas often volunteer in garden settings around established bushes, and plants can be found at almost any plant sale or from friends who have rose of Sharon growing in their yards. They are easily rooted from cuttings taken in June and July, and seeds come up readily. If you want a plant exactly like the parent, rooted cuttings will be your best bet, as seedlings may be different from the parent. 

Problems 

While altheas are usually easy to grow and trouble free, a few problems can crop up. If plants get too much or not enough water, bud drop can occur. Mitigate this problem by mulching with a layer of organic mulch to help keep moisture levels from fluctuating.  

Fertilize carefully, and on the spare side of recommended rates as too much fertilizer can also cause buds to drop. Lots of tender new growth may cause aphids to be attracted to the plants. Pinch off twigs that are visibly infested, or wash them off with a strong jet of water.

Kinds 

Most of the althaeas that grow and reseed freely are old-fashioned, pass-along plants. Many of those more recently introduced, however, are sterile triploids that set no seed. Select one of these to prevent seedlings from escaping into your landscape. Choose from the pure white ‘Diana’, the white with maroon throat ‘Helene’, the beautiful pink ‘Aphrodite’, lavender ‘Minerva’, and more recently the lavender-blue ‘Bluebird’.

At a Glance

Scientific name: Hibiscus syriacus

Say: high-BISS-kuss seer-ee-AY-kuss

Common Name: Althea (or althaea), rose of Sharon

Family: Malvaceae (Mallow family)

Relatives: Hibiscus, hollyhock, abutilon, okra

Hardiness: USDA Zones 5-9

Origin: China and India

Propagation: Seeds, cuttings

Salt tolerance: Moderate

Size: 8-12/4-10 feet tall/feet wide