Kerria, or Jew’s mallow, is a bushy, deciduous shrub with graceful curving basal shoots, bearing bright yellowin April and May. It is most commonly seen in its double-flowered cultivar, ‘Pleniflora’, or ‘Bachelor’s Buttons’, which grows much taller than the single-flowered species, reaching 3m (10 if) or more. It is quite hardy, but in cold northern sites it is happier grown against a wall.
It is a curious fact that the double-flowered form of Kerria japonica is markedly different in habit from the single form, with much longerwhich can readily be trained against a wall or over a screen, whereas the single variety forms a 4 to 5-ft. High thicket of growth, constantly spreading by suckers. Both are useful but it is the double form, pleniflora (or florepleno), which is most popular. Its little, buttercup-yellow, pompon flowers are freely produced in late spring. Both kinds will grow well in any reasonably good, not too dry soil and can be pruned after flowering, when some of the older stems can be cut out and those that are too long can be shortened.
General care: Kerria are happy with any ordinary soil, and a sunny or half-shady site. Plant any time during the winter. They should be pruned every year as soon as they have finished flowering. Cut back the flowered shoots to promote the new growth on which the plant will flower next year. At the same time remove a few of the old shoots at ground level to promote new basal growth.
Propagation: The easiest way is to divide the clump of shoots any time during the winter. Alternatively, takefrom the lateral growths at the end of the summer, and strike them in 50-50 sand and peat.
Pests and diseases: Generally trouble-free, but somemay go chlorotic, turning yellow or white in the areas between the veins, under certain, very alkaline, soil conditions. Treat with chelated iron.