The Hibiscus syriacus, or althea, is a popular natural fencing or border shrub in cold hardiness zones 5 to 8. Also known as the rose of Sharon, this shrub loves to show off its grand, papery flowers just as other blooms are beginning to fade in the late summer's heat. A member of the hibiscus family, the althea grows erect and tall, covered in compact green leaves and a multitude of single or double blooms in colors from the red and purple family, as well as white and even a fairly true blue. Carefully prepare the site and follow maintenance procedures to ensure that your althea will be drawing gazes in late summer for many seasons to come.
Choose a planting site with good drainage in full sun to part shade. Drainage is the most essential component of a proper planting site, because pooling water around roots spells death for most landscape plants and shrubs. Allow ample space for the althea to mature, because it will reach a height of up to 12 feet and spread out as much as 10 feet.
Prepare the site by tilling the soil to the depth of your althea bush container or at a depth equal to the height of the root ball. As you cultivate the soil, remove clods of dirt and rocks. Tilling soil provides pockets for roots to spread out and improves soil drainage. Clemson University Cooperative Extension horticulture specialists suggest the addition of organic matter, such as composted pine bark, at a ratio of 10 to 20 percent of the bed's total soil volume. If the site has especially poor drainage, opt for a raised bed created by mounding the prepared soil up to 12 inches with tapered edges to allow water to flow away from the root ball.
Remove the shrub from its container or cut the burlap wrap from the outside of the root ball. If there are roots encircling the ball, make side cuts no deeper than 2 inches vertically at up to four places to loosen the roots.
Dig a hole with a depth equal to the height of the shrub's root ball. Set the root ball on the undisturbed soil at the base of the hole for support. Gently fill the base of the hole with the prepared soil, tamping lightly with your foot as you add layers of soil. Avoid firming the soil too much as the roots will become trapped.
Add a 2-inch layer of organic mulch, such as pine needles or cut leaves, over the planting area. Avoid contact between the mulch and the tree trunk which can cause rot issues.
Water around the root ball and keep this area moist, but not soggy, with deep consistent watering rather than frequent shallow applications. Watering too much or too little can lead to death in the first season after planting, so carefully monitor the needs of the althea in your particular soil and climate.
Prune in late fall or early spring since flowers grow on new wood, meaning the current season's new growth. Purdue University extension experts suggest that you prune up to one-third of the new growth by cutting back to about 1/4 inch above a bud where leaves form. Pruning yearly will generally result in fewer, larger flowers. An abundance of smaller flowers results from infrequent or no pruning.