There Kerria o Kerria japonica o Rose of Japan, it’s a shrubby plant native to Asia, where it is called Yamabuki, cultivated in gardens and parks for ornamental purposes.
General characteristics of the Kerria japonica
It is a perennial shrub belonging to the Rosaceae family.
The plant has a robust root system that produces thin, hanging green stems covered with alternate leaves having a lanceolate – ovate shape with doubly indented margins.
Read also: Spirea of Japan – Spiraea japonica
During the flowering period so many bloom flowers, particular yellow-amber inflorescences similar to small roses with simple or compound corolla, depending on the species.
Kerria blooms twice a year; the first spectacular and abundant flowering occurs in spring, the second in late summer with few and isolated flowers.
Cultivation of Kerria
Kerria is a shrub that, in order to develop vigorously and to bloom profusely, requires sunny positions in harsh climate areas while in mild climate areas it can also be placed in semi-shaded areas if you want to avoid discoloration of the flowers. It has no problems with the cold, while it cannot stand the sultry heat that causes the foliage to dry out and inhibits autumn flowering.
Although it adapts to all types of soil, it prefers a fresh and deep substrate, rich in humus, always well drained. It does not tolerate clayey soil in the least.
You may be interested in: Asebo – Pieris japonica
Generally this plant is satisfied with the rains but in periods of prolonged drought it should be watered when the soil is completely dry. Shrubs grown in pots should be watered regularly.
At the end of winter, to encourage flowering, sprinkle slow-release organic fertilizer at the foot of the plants. During the spring, every 20-25 days, administer a fertilizer rich in nitrogen and potassium, to be diluted in the water used for irrigation.
Kerria: growing in pots
This splendid plant with its abundant flowering is ideal for embellishing balconies and terraces and exposed to the sun or at most partially shaded.
Do you have problems with plants? Join the group
The pot must be larger than the earthen bread that surrounds the roots of the Kerria purchased in the nursery, in general (min 50 x 50 x 50 cm).
The ideal growing medium is a mixture consisting of fertile soil with peat and sand. Expanded clay or coarse gravel should be used as drainage material for the bottom of the pot.
After being invaded, the plant should be regularly watered and then placed in the chosen place. It should be regularly fertilized with a specific fertilizer for green and flowering plants and protected from the cold as soon as the winter temperatures become harsh.
Kerria shrubs grown in pots require repotting every 4 years. A new container larger than the previous one and new fresh and fertile soil, always well drained, is used to avoid root rot.
Multiplication of Kerria
The Kerria reproduces by division of the tufts, by cutting and by detaching the suckers.
The division of the tufts takes place in the autumn – winter period.
Propagation by cuttings
Propagation by cuttings of suckers takes place in summer.
The cuttings, 15 cm long, taken from the lateral branches are put to root in a mixture of peat and sand. Once rooting, the young seedlings are raised in individual containers until the following autumn and then planted in the ground.
Planting or planting
The Kerria can be planted in the open ground without problems, from spring to autumn, from October to March in well-worked soil rich in organic substance. If you intend to create a hedge, the recommended distance between one plant and another is 1.50 meters.
Kerria plants match perfectly with other bushy plants that bloom in April-May, such as Deutzia, Philadelphus, Spirea, Crataegus, Cornus etc.
Kerria like Forsythia, after flowering, needs rejuvenating pruning in order to favor the appearance of flower buds in the following spring. Dry or damaged stems are pruned at the base, long and disordered ones are shortened. If you want to contain the excessive development of the bush, some basal suckers are also removed, which also develop at a distance from the mother plant. Pruning should be done immediately after the summer flowering and not before because the Kerria blooms on the branches of the previous year. For the pruning operation it is recommended to use well sharpened and disinfected shears.
Kerria diseases and pests
Although it is a rustic and resistant shrub, it is sometimes attacked by some fungal diseases that cause the leaves to yellow or compromise their aesthetics with the formation of showy brownish spots.
Among the animal parasites it suffers from the attack of caterpillars that damage the roots, mites and aphids that ruin the foliage.
Cures and treatments
The Kerria must be protected from intense frosts that can affect the base with a good mulch of straw or dry leaves and also with non-woven fabric readily available in nurseries.
Phytosanitary treatments should be applied only if necessary and using biological pesticides that are not harmful to pollinating insects such as the garlic or nettle pesticide, easy to prepare even at home and at almost zero cost. Infected plants should be treated early in the morning or after sunset on a sunny, non-windy day.
Variety of Kerria
The genus includes several varieties grown for ornamental purposes.
Kerria japonica pleniflora
The most widespread species and cultivated in gardens due to the prolonged and abundant flowering that goes from May to June. It forms a bush up to 3 meters high composed of arched and flexible stems covered with a light green and shiny bark. The leaves are deciduous; they have an elliptical-lanceolate shape with serrated edges and a dark green lamina which turns to purple in autumn.
The flowers are double, similar to golden yellow pompoms. It can be grown in full sun or partial shade in common garden soil. It is used as a single element, in groups or in rows in hedges.
Kerria japonica pleniflora, so named for the double flowers, is also known by the synonym of Corchorus japonicus.
The Kerria picta It is a 120-120 cm tall variety, with creamy white mottled leaves along the margins. During the flowering period it is covered with simple lemon yellow or creamy white flowers. It is grown in full sun or partial shade in a place sheltered from the winds.
Kerria Picta variegata
It is a variety that forms 1 meter tall and wide bushes with stems covered with green leaves with white variegations and creamy white flowers.
Kerria is widely grown in private gardens, in public parks as a single specimen and in groups to create beautiful flowering hedges.
Meaning of the Kerria
In the language of flowers, Kerria symbolizes creativity and serenity.
Is Kerria poisonous?
This beautiful ornamental plant can be grown without any problems as it is not toxic to humans, dogs, cats and other pets.
Kerria bears its name in honor of the English botanist William Kerr who first introduced it to Europe, in the botanical garden of Kew.
In Japan, Kerria japonica is called Yamabuki, which means golden yellow and is synonymous with prosperity and health.