Aside from the great height and beauty of Rose of Sharon, it is also an easy plant to propagate. You have three ways to choose from, all of which should be begun in the fall. Keep in mind the vigorous nature of Rose of Sharon, and be sure you select a site in full sun with rich, loose soil.
Collect the seeds from the plant once the seedpods have dried and are opening. Store the seeds in a cool, dry place in an envelope until six to eight weeks before your last frost in spring.
Start your seeds 1/4 to 1/2-inch deep in individual pots. Water well to moisten, but do not soak the soil. Place the pots into individual plastic bags.
Set the pots and bags in a sunny window for the seeds to germinate, which takes about two weeks. When they are 2 to 3 inches tall, remove the bags and continue to maintain the plants in moist soil until your last frost has passed and the plants are too large for their pots.
Select pencil-thick branches coming off strong stems once the leaves have fallen off the plant. Look for branches 9 to 12 inches long that have a firm tip.
Cut the branch off at the point where it joins the main stem. Make a top cut just above a bud and a bottom cut just below a bud to form a full 9- to 12-inch cutting. Many branches may supply two or more cuttings depending on their starting length.
Dig a 6- to 8-inch deep trench and fill the bottom with 1 to 2 inches of sand or perlite. Set your cuttings vertically into the sand, spacing them 4 to 5 inches apart. Fill in the trench with the same soil you had removed to bury just over half of the cutting.
Water to keep the soil moist for the first month, then weed and water only as needed throughout the following year. During the second spring you can transplant the cuttings to their permanent location. Leave weaker cuttings to grow for another year before transplanting.
Dig up your existing plant and divide the root ball in half vertically. Divide it vertically once more to break the plant into quarters.
Continue to divide the plant until the root balls are about the size of a grapefruit. Larger, older plants may need more divisions than smaller ones to get to this size.
Plant each new division in a permanent location and water well for the first month. These divisions may need two growing seasons to root before you see blooms on them.