Green Guide: Kerria japonica

Kerria japonica 'Pleniflora'

There are so many things to admire about Kerria japonica that set it apart from the usual suspects seen in the garden. It’s a gorgeous bloomer in shade, with long-lasting flowers, making it a champion in difficult shady spots that warrant a large shrub, as well as in areas of the garden needing a graceful focal point. The evergreen stems provide winter interest, and are a great contrast against both snow and dark-colored structures. The plant is easy-going and low-maintenance, drought-resistant, blooms for a long period of time, and will grow nearly anywhere.

K. japonica is a small ornamental shrub that typically matures at 5-8 feet tall by 6 feet wide. Its arching or weeping clump growth habit becomes rounded by age. The Kelly-green branches are slender and smooth, and retain their color throughout the winter. This is a great plant for winter interest, especially against a background of snow, as well as against red bricks or dark siding.

The foliage emerges a bright medium-green color in early spring, changing to a darker green as the season progresses. The alternating leaves are ovate, and have doubly serrated edges, making a nice contrast to large-leafed or lanceolate plants like hostas, iris, lilies, and daffodils. The leaves hold late into the fall, and drop leaving the green stems behind.

Kerria is hardy in USDA Hardiness Zones 4-9, and grows well in both part shade and full shade. In full sun, the plant grows well and purportedly flowers more, but the flowers bleach to a paler yellow. It grows best in a moist, well-drained, slightly acidic soil, but will tolerate poor soils and an assortment of soil pHs. Kerria is both heat and drought tolerant. It has few disease or pest problems — leaf spot and twig blight are reported as potential problems.

Some cultivars
Kerria flowers make this plant shine. The most commonly available cultivar, ‘Pleniflora’ (also known as ‘Flora Pleno’), bears dozens of 1½-inch golden-yellow double flowers that resemble small pompon-shaped mums. Each flower lasts for two to three weeks. Although the primary bloom period is spring, Kerria flowers sporadically throughout the summer, and then puts on a good show once again in late August or early September.

— University of Illinois Extension, Cook County