Only the japonica species, native to Asia, belongs to the genus Kerria; it is a medium-sized shrub, which reaches 200-250 cm in height, with a rounded shape.
The stems of the kerria japonica are thin, arched, poorly branched, each plant produces numerous basal shoots, which tend to develop quite rapidly.
The foliage is deciduous, of small dimensions, of dark green color; the leaves have a serrated or serrated edge.
In spring, from March to May, it produces countless small golden-yellow flowers, with five petals, similar to small yellow roses.
Many cultivars can be found on the market, the most widespread is K. j. pleniflora, with double flowers, similar to small pompons; there are also cultivars with white flowers, or with delicately variegated foliage.
Generally the spring flowering is very abundant, followed by a second flowering in late summer, with the production of a few scattered buds. Plant widespread in the gardens of the past, especially in the case of the Pleniflora variety, now it seems to be enjoying a second youth, even if in recent years the varieties with simple flowers are spreading particularly.
The kerrie of Japan tolerate any exposure, from full shadow to full sun. Generally the plants placed in total shade tend to produce few flowers, while the buds of the specimens in full sun are of short duration and tend to whiten with exposure to sunlight.
There kerria japonica It is a shrub decidedly suited to the partial shade, where its flowering is abundant and long lasting and the growth of the plant is quite vigorous.
These plants bloom on the branches of the previous year, so it is advisable to do the pruning after the spring bloom.
This japonica variety prefers medium-textured soils, quite deep and rich, very well drained. Avoid planting this plant in place with water stagnation or with very heavy and poor soil.Multiplication
In autumn, or at the end of winter, they separate the new stems that form at the base of the mother plant. You can also make cuttings, 10-15 cm long, taking them from the side branches in summer and planting them in a cold box without needing protection. Also in the summer it is also possible to make the layering that, without many difficulties, will take root in a short time.
Kerria of Japan - Kerria japonica: Pests and diseases
Particularly dangerous for Japanese kerries are the mushrooms of the genus Cylindrosporium, which attack the shoots and lead to the drying of the leaves. The best thing is to cut both the tips and the diseased leaves. In addition to this, there is also the currently sporadic presence of Blumeriella infections.
Among insects, caterpillars can attack the roots and cause serious damage.