Kerria japonica Pleniflora - Japanese Rose

Kerria Japonica 'Pleniflora' is such a widespread variety of Japanese kerria in gardens that it almost makes us forget the botanical type species. Its popularity has endured over the years, thanks to its abundant spring flowering of yellow pompom-like blooms, which complements its attractive green foliage so well. Fairly fast-growing, this shrub reaches 2 m in height and more in width. Very hardy, it adapts to most ordinary soils, except those that are too dry or too wet. Its deciduous foliage turns yellow before falling, revealing the pleasing architectural form of its slender stems, which are the same green as the leaves.

Kerria is a member of the large Rosaceae family, which includes nearly 5,000 species of plants native to our countryside and forests (wild cherry, blackthorn, wild strawberry...), the vast majority of our fruit trees (apple, pear, peach, cherry...) and a multitude of ornamental genera, such as Sorbaria, with its elegantly divided foliage, or Pyracanthas, with their highly decorative fruits. Japanese kerria is a monospecific genus which, despite its species name, originates from western and central China and has long been grown in Japan. The variety Kerria japonica 'Pleniflora' was the first to be introduced to Europe, at the Jardin du Roi in Paris, sent in 1784 by the Swedish naturalist Thunberg from Japan. The type species, K. japonica, with single flowers, did not arrive until 1834 and remains far less widespread today. Double-flowered Japanese kerria is a very popular shrub found in many parks and gardens, as it is easy to grow, hardy and highly ornamental. It develops slender, flexible and arching branches, with fairly vigorous growth. These soon form a dense, rather impenetrable clump over time if the plant is not pruned from time to time. At maturity, the plant reaches 2 m in height, or more, and 2.50 m in width, but its growth can be reduced if necessary by pruning annually immediately after flowering. The alternate leaves are deciduous, measure 3 to 6–7 cm in length, and are double-toothed along the margins and pointed at the tips. Medium to bright green, slightly pleated or veined, they appear just before or at the same time as flowering in April. At this time of year, the shrub is covered in very double, bright golden-yellow flowers, which open until May. Measuring 3 to 4 cm in diameter, they develop on the previous year's branches. They are solitary but very numerous, as they colonise the branches along their entire length, producing a quite spectacular mass effect in spring. Unlike the type species with single flowers, the plant is not very nectar-rich, because the petals are so numerous and tightly packed that they hinder pollinating insects. In autumn, the foliage turns yellow before falling to the ground, although it cannot rival plants with autumn colour such as the famous maidenhair tree.

Easy to grow in most soils and climates, and only truly sensitive to severe drought or excessive lime, Kerria japonica 'Pleniflora' is popular for good reason. Its spring flowering is truly dazzling, and its green wood remains decorative in winter after the leaves have fallen. You will achieve an attractive effect by incorporating it into an informal hedge alongside other free-flowering shrubs with a flexible habit, such as Van Houtte's spiraea, with its immaculate white flowers, or the splendid Berberis 'Orange King', with its countless flowers of a rare orange shade. Also consider adding a few shrubs with autumn colour, such as spindle 'Red Cascade', which blazes bright red while producing an attractive display of decorative fruit.