Japanese kerria (Kerria japonica) is an underused, early flowering, deciduous shrub that thrives in full to part-shade landscapes. It is somewhat unique among flowering shrubs that kerria blooms profusely in partial shade. The flowers are bright golden yellow with five petals – very similar to an old-fashioned rose. It has a bloom time that begins in late March to mid-April in Upstate South Carolina, and flowering lasts for a couple of weeks. Although another common name is Japanese yellow rose, most people recognize this shrub by its genus name, Kerria.
The name Kerria comes from the Scottish plantsman and collector, William Kerr, who returned from China with specimens for Kew Gardens in 1805. Plants are cold hardy and grow well in USDA zones 4 to 9, which includes all of South Carolina.
Mature Height & Spread
Depending on the cultivar, the height ranges from 3 to 8 feet tall and the spread is up to 6 feet wide; however, the plants tend to slowly sucker and form small colonies. Branches are green, upright, and arching, so the growth habit becomes rounded with age. Stems remain thin and have an interesting zigzag appearance.
Japanese kerria is considered a small ornamental shrub. The foliage is bright green, doubly serrated, and has a chartreuse fall color. Its simple leaves are birch-like in shape and alternately arranged on the stems. The plant has a fine texture with its small leaf size (1½- to 4-inches long). Due to its ability to flower profusely in partial shade to shade, this deciduous shrub is a useful addition to a woodland landscape. Flowering is for a 2- to 3-week period. The Kelly green stems add to winter interest. Established plants are drought tolerant and deer resistant.
Prune Japanese kerria soon after flowers have dropped in early to mid-spring (late March to mid-April). Heavy pruning can be used to rejuvenate old, over-grown plants and to enhance flowering and plant shape. Best flowering is under partial-shade conditions, and plants may re-bloom sporadically during the summer. Fertilize shrubs lightly in spring with a slow-release fertilizer. Japanese kerria does not tolerate heavy, poorly drained soils, so planting areas should be amended with compost to improve internal soil drainage. Mulch shrubs lightly to conserve soil moisture and weed competition.
Plants sometimes become infected with kerria twig and leaf blight, a fungal disease caused by Blumeriella kerriae, which produces leaf spots and stem lesions, and may result in severe defoliation. Numerous small red-brown spots with purple borders form on foliage. Spots typically coalesce (merge) and cause the leaves to turn yellow to brown and then drop from the plant. Lesions on the stems are purple-brown, elliptical cankers, which can girdle the stems causing dieback. If leaf spots are present, bi-weekly sprays with chlorothalonil (Daconil) during wet summer weather can significantly reduce the spread of the disease. Heavy pruning to remove diseased stems in summer, followed by raking and disposing of fallen foliage in autumn can help eliminate the disease. Irrigate plants with soaker hoses or drip irrigation, but do not wet the foliage.
Japanese kerria can be propagated very easily from softwood cuttings. Take terminal stem cuttings for rooting between May and July. A better root system develops by applying a rooting hormone (containing IBA) to the cuttings. Examples are Miracle Gro Fast Root Rooting Hormone, Ferti-lome Rooting Powder, Bonide Bontone Rooting Powder, and GardenTech Root Boost. Alternatively, because the plants tend to sucker, dig sucker growth from around the perimeter of the shrub and replant.
Besides the single-flowered, straight species of Japanese kerria, there are a few commonly sold cultivars.
- ‘Pleniflora’ – Introduced by William Kerr in 1805 from Asia, this double-flowered cultivar has 2-inch wide, chrysanthemum-like flowers with an orange-yellow hue. Plants may become larger than the single-flowered species and can reach a height of up to 8 feet.
- ‘Golden Guinea’ – This cultivar is a single-flowered form with large, 2½-inch wide flowers and a long bloom period. Flowers are slightly fragrant. Plants grow to 5 feet tall and 4 feet wide.
- ‘Picta’ – This variegated cultivar has leaves with creamy-white margins. However, like many variegated plants, it is slower growing and tends to revert to branches with green foliage, which must be pruned out.