Clethra Propagation

Softwood Cuttings

• Most sweet pepperbush shrubs propagate readily from softwood cuttings, which root best in summer when the shrubs grow actively. Little preparation or special treatment is required to start the cuttings, although they root fastest and most prolifically if treated with indolebutyric acid (IBA) rooting hormone with a strength of 0.1 percent, or 1,000 parts per 1 million. The cuttings should be taken from young, pliant branches, which have no flowers or buds, then potted in a sterile medium such as perlite or milled peat moss. Healthy cuttings root in roughly one month if they are kept in a lightly shaded area and receive frequent misting.

Seeds

• Sweet pepperbush hybrids or cultivars may produce an abundance of seeds, but the seeds seldom grow true to type, or true to the parent plant's characteristics. Therefore, seed propagation typically is reserved for non-hybrid shrubs. The seeds exhibit no dormancy and germinate rapidly if sown while still fresh and exposed to temperatures of about 70 degrees Fahrenheit. Their soil, however, must be kept moderately moist for the duration of the germination process to ensure a successful outcome.

Division

• In addition to softwood cutting and seed propagation, the number of sweet pepperbush shrubs can be increased through division. Only a mature, well-established shrub should be divided because cutting apart the roots of a younger specimen may cause irreparable damage. The process works best in late autumn or winter when the shrub is dormant. Simply prune back its branches to roughly 6 inches long, dig up its root ball and cut the root ball into large portions, each with an equal share of roots. Transplant the divisions directly into a prepared bed, or grow them in pots until the following autumn and plant them then.

Care and Planting Procedures

• Cutting- and seed-propagated sweet pepperbush shrubs require a longer establishment phase than divisions because they must have time to develop functioning root systems before they are planted in a garden. Grow the young, newly grown shrubs in containers for one full growing season before planting them in the garden. Provide them very light shade and weekly watering during the summer months to prevent dehydration and to encourage robust root growth. In autumn, plant the shrubs in a prepared bed that has acidic soil and receives light, dappled shade.