Kerria is a member of the Rosaceae (rose) family, and was named after William Kerr, who introduced the cultivar 'Pleniflora' in the early 1800's. Kerr was a British horticulturalist who is also credited with introducing the Rosa banksia to Kew Gardens, from what was then called Canton, China. Kerria earned its species name japonica because it is native to Japan, and in fact is sometimes called the Japanese rose. Another common name, Easter Rose, comes from the fact that it is typically in bloom at Easter time.

Form and Foliage

This small ornamental shrub typically matures at five to eight feet tall by six feet wide. It has an arching or weeping clump growth habit, which becomes rounded by age. The branches are very slender and smooth, more like stems, and consequently the shrub has a rather airy, fine-textured feel to it. The stems are a bright kelly green, 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, then drop leaving the evergreen stems behind.

Flowers

This is where Kerria literally shines. The most commonly available cultivar, Kerria japonica 'Pleniflora' (also known as 'Flora Pleno'), bears dozens of 1.5" double-flowering, bright golden yellow flowers that resemble small pompon-shaped mums. In April and May, they are among the first flowers in our garden, and positively glow, especially in contrast to the green stems. Each flower lasts from two to three weeks, and although they are supposed to be more abundant in full sun, our shrub–located in the northeast corner of the yard and receiving perhaps three hours of sun each day–is still constantly in bloom. Although the primary bloom period is springtime, we have found that Kerria flowers sporadically throughout the summer, and then puts on a good show again in late August or early September.

This year, I managed to find a rarely available single-flowered cultivar, Kerria japonica 'Honshu', and excitedly bought two plants even before I knew where to plant them! This varietal has larger, two-inch single sunny yellow flowers, whose petals overlap and give a fuller effect. The shrub has the same arching habit, but is slightly smaller, growing up to five feet tall but only three feet wide. (Interestingly, the plant tag gave it the common name "Bush Clover", which actually appears to be Lespedeza virginica, from the pea family Fabaceae. All the more reason for plant tags to give the scientific name, as well as the common name!)

At the same nursery, I also found a white-flowered cultivar, Kerria japonica 'Alba'. It shares the smaller habit with 'Honshu', but the white flowers, each with a tiny yellow center, did not have that same luminous presence, and so I took a pass on it. I have also read of the variegated cultivar 'Picta', which apparently has gray-green leaves edged in white. This is a shorter plant, growing less than four feet tall, and is said to be less floriferous than the species.

Culture

Kerria is rated for Zone 4 through 9, and grows well in both part shade and full shade. In full sun, the plant still does well and supposedly blooms more, but the flowers bleach to a paler yellow. It prefers a moist, well-drained, slightly acidic soil, but will tolerate poor soils and an assortment of soil pHs. Happily, Kerria is both heat and drought tolerant and survived last year's lack of rain with aplomb. It has few disease or pest problems; leaf spot and twig blight are reported as potential problems, but our specimen has shown signs of neither in its 25-year sojourn in the garden.

This plant is tolerant of heavy rejuvenation pruning, although it rarely needs much pruning except to rid it of some minor die-back. The central stems on mature plants may dieback in winter especially if cited in poorly drained soils, and should be removed in early spring. On occasion, we have pruned some of the arching stems that partially obscured the totem pole behind it, more for effect than because they were a nuisance. The bonus here was that we took the stems inside and put them in water, for a month's worth of golden flowers.

Several sources I consulted warned of Kerria's mildly invasive potential, as it spreads underground by peripheral suckers unless the roots are restricted by its site (for example, next to a foundation or sidewalk). I must admit, this came as news to me, as our Kerria has stayed tidily in its little corner for its entire quarter-century life. If this is an invasion, then it is by foot soldier and not the armored division; my guess is that invasiveness might be more of a problem in full sun. Should spreading growth be a bother, it would need to be dug out.

Kerria is said to be rather easy to propagate, either by cutting or by division. Its fruits are small, brown, and ornamentally inconspicuous.

An Overachiever

There are so many things to admire about Kerria that set it apart from the usual suspects we see in the garden. It's a gorgeous bloomer in full 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. What more can you ask?

To view photos of Kerria japonica, see the 'Pleniflora' cultivar at Auburn University's website at http://www.ag.auburn.edu/hort/landscape/337.html and the single-flowered varietal at Dave's Garden, http://davesgarden.com/pf/go/157/ .

MaryAnne Spinner, Chicago Master Gardener

Do you have a gardening question? Email the Extension's Electronic Plant Clinic at rwolford@uiuc.edu, and our Master Gardeners will be glad to assist you.