Japanese Kerria

(Rosaceae - Rose Family)

Form

• small ornamental shrub
• maturing at up to 5' tall by 6' wide
• arching clump growth habit, becoming rounded with age
• rapid growth rate from its basal shoots, but slow growth rate from the established stems

Culture

• full sun to full shade
• prefers a moist, rich, well-drained, slightly acidic soil in partial sun, but will tolerate poor soils, various soil pHs, heat, drought, and various sun or shade conditions
• propagated primarily by rooted stem cuttings, but also by separation of the rooted suckers
• Rose Family, with few disease or pest problems, although death of the older, usually central stems in the Winter is fairly common with mature shrubs
• moderately available in container form
• tolerant of heavy pruning, which can be used to rejuvenate old plants

Foliage

• emerging as a bright medium-green color and changing to dark green as the season progresses
• deciduous, alternate, ovate to lanceolate, doubly serrated, with impressed veins and an acuminate apex
• green to chartreuse fall color that is persistent into November

Flowers

• bright golden-yellow, in April and May and sporadically throughout the Summer
• 1.5" diameter solitary flowers can be very dense on the stems if sited in full sun
• each golden-yellow flower is effective for two to three weeks and has a good contrast against the green foliage background

Fruits

• small, brown, and ornamentally inconspicuous

Twigs

• bright kelly green, even in Winter
• stems are very thin, somewhat zig-zag, and have small brown conical winter buds
• dead stems are white-brown, noticeable, and often in the center of mature shrubs, and should be annually removed every late Winter or early Spring

Trunk

• not applicable

ID Summary

• thin kelly green evergreen stems, which zig-zag at the stem termini, and bleach out to a white-tan color when they die
• golden-yellow button-mum-like flowers in Spring
• alternate leaves are ovate, with doubly serrated margins, impressed leaf veins, and a long acuminate apex

USAGE

Function

• foundation, specimen, group planting, or mass planting shrub, good for naturalizing in the border or in erosion control situations
• good Winter stem contrast against red brick or white stone walls

Texture

• medium-fine texture in foliage and very fine-texture when bare
• open to average density in foliage but thick density when bare (for mature plants)

Assets

• evergreen (light green) stems on a deciduous shrub
• showy yellow flowers in late Spring and sporadically thereafter
• rapid growth and vigor once established

Liabilities

• spreads underground beyond its original space and is invasive by peripheral suckers, except in a root-restricted site (such as in a raised bed, or between a sidewalk and a foundation)
• central stems on mature plants often dieback during Winter (especially when sited in poorly drained soils) and turn off-white, and result in necessary maintenance for their selective removal in early Spring

Habitat

• zones 4 to 9
• native to China

SELECTIONS

Alternates

• shrubs with Winter stem appeal (Acer palmatum 'Sango-kaku', Chionanthus retusus, Cornus sericea cultivars, Corylus avellana 'Contorta', Cytisus cultivars, Euonymus alata [the corky-stemmed species form], etc.)
• shrubs with showy yellow flowers in Spring (Cornus mas, Forsythia hybrids, Hamamelis x 'Arnold Promise', etc.)
• arching shrubs of fine texture (Lespedeza thunbergii, Salix purpurea 'Nana', Tsuga canadensis 'Pendula', etc.)
• naturalizing shrubs that can be used in the border or for erosion control (Acanthopanax sieboldianus, Cornus alba, Lonicera species, Rhododendron cultivars, Salix purpurea, Sambucus canadensis, etc.)

Variants

• Kerria japonica 'Picta' - gray-green leaves are irregularly variegated white on the extreme outer margins; a very good variegated shrub for partially shaded to fully shaded sites, but of low availability
• Kerria japonica 'Pleniflora' - has double-flowering, golden-yellow flowers that resemble miniature button mums

NOTES

Translation

• Kerria is named after William Kerr, who introduced the cultivar 'Pleniflora'.
• japonica translates as "from Japan," where it is also grown.

Purpose

• Japanese Kerria is a fine-textured deciduous shrub with thin evergreen stems that are subtlely ornamental in Winter, and also with good Spring yellow flowers.

Summary

• Kerria japonica is an upright to arching, green-stemmed shrub with golden-yellow late Spring and sporadic Summer flowers.