Sickly looking yellowing shrubs don't exactly make a gardener feel accomplished, but if you can diagnose the problem, chances are you can turn it around. An acidic-loving shrub, "Harbour Dwarf," (Nandina domestica "Harbour Dwarf") is prone to chlorosis. This 1- to 2-foot-tall plant grows in U.S. Department of Agriculture plant hardiness 6 through 9. The dwarf is a cultivar of what is commonly called Heavenly Bamboo, which is invasive in some areas.
"Harbour Dwarf" nandina needs acidic soil to thrive. In alkaline soil, it can develop chlorosis, a condition caused by an imbalance in the soil pH. "Harbor Dwarf" nandina thrives in soil with a pH between 3.7 to 6.4. If you notice yellowing foliage, take a soil pH test--you can get kits at most garden centers--to determine the acidity of your soil.
Don't mistake chlorosis for seasonal foliage change. In USDA zones 6 through 8, where "Harbour Dwarf" is deciduous, the leaves turn from green deep purple and rich orange in the fall. After the dramatic foliage show, the shrub sheds it's leaves over the winter. In zones 8 and warmer, where "Harbour Dwarf" grows as an evergreen, you won't get the fall color or the annual leaf shedding.
Lowering your soil's pH can be accomplished with natural ingredients. Mulch with acidifying qualities, such as pine needles or bark, will lover the pH over time. Apply the mulch 2- to 3-inch-deep around your "Harbour Dwarf." Replenish the mulch annually as it breaks down, but don't let the decomposing mulch go to deep into the soil where it may suffocate the roots.
Horticulturalists and commercial growers use sulfur to correct a high soil pH, but the risk of burning existing plants makes it difficult for use in an established shrub bed. If your "Harbour Dwarf" has turned a sickly yellow due to high soil alkaline levels, consider digging it up and moving it to a naturally acidic area. You can also grow this dwarf nandina in a container using an acidic potting soil.
Though the nandina cultivar "Harbour Dwarf" is hardy to USDA zone 6, where winter lows fall to around -5 to -10 degrees Fahrenheit, some or all of the foliage and stalks can die back when temperatures drop to 0 F, but they will recover according to University of Florida IFAS Extension. Hold off pruning until early spring. To rejuvenate a frost damaged dwarf nandina, cut it back to 6 inches above the soil. Use a pair of shears and cut carefully so you don't cut any new shoots coming up. Before and after pruning, sanitize your tools in a mixture of equal parts rubbing alcohol and water.
- Missouri Botanical Gardens: Nandina Domestica "Harbour Dwarf"
- University of Florida IFAS Extension: 'Harbour Dwarf' Nandina (Nandina domestica): Noninvasive in South Florida and Recommended with Caution in Central and North Florida
- San Marcos Growers: Nandina domestica 'Harbour Dwarf' - Harbour Dwarf Heavenly Bamboo
- Clemson Cooperative Extension: Pruning Shrubs
- Virginia Cooperative Extension: Nandina Heavenly Bamboo
- University of Minnesota Extension: Mulching the Home Landscape
- Organic Gardening: How to Lower your Soil pH