Taxonomy and Botany of Japanese Rose
Kerria japonica plants are deciduous flowering shrubs.
Japanese rose shrubs bear yellow flowers in spring and can provide additional blooming later in the summer. Mine bloomed for 6 weeks one spring, were without flowers for the following 6 weeks, then offered a second blooming that lasted the rest of the growing season (although sparser than the spring flowering).
I grow a double flowering type that produces a pompom-style blossom, but single flowering Kerrias are preferred by some.
Japanese rose's bark and branches are also of interest. The main branches on the double flowering type arch gracefully to a height of 8-10 feet (the width can be restricted to similar dimensions through general pruning and, specifically, the removal of suckers). Smaller branches radiate off the main ones in all directions. The branching pattern thus affords interest both vertically and horizontally; it is also relatively airy. The bark is a pleasing kelly green to greenish-yellow, to boot -- a color retained throughout the winter.
Native Origin, Planting Zones, Sun and Soil Requirements
Grow the bush in partial shade. It is one of the most shade-tolerant of the deciduous flowering shrubs (in terms of shade not stunting flower production), earning it a spot on my list of the top shrubs that grow in shade.
The plants, themselves will also do fine in sun, but sun causes the color of the flowers to fade quickly.
Japanese rose is not overly fussy about soil pH; just give it a loamy soil. It will also tolerate poor soils but may perform better in soils enriched with humus. The ground should be kept evenly moist around Kerria japonica, which prefers a well-drained soil.
Its shade tolerance gives you the option of having a deciduous flowering shrub in a partially shaded area, while the profusion of blooms on the bush makes it a spring standout. Do not underestimate the importance, however, of Japanese rose's attractive branches, which provide much-needed visual interest for the winter landscape. In this sense, Japanese rose branches remind one of those on red twig dogwood and yellow twig dogwood. Choose a background against which the branch color can be displayed to optimal effect; for example, Japanese rose's kelly green stems would look terrific against a barn-red shed.
Plant Care (Pruning), and a Major Drawback
The plant blooms on old wood in early-to-mid spring; prune just after its spring flowering is over. A second flowering later in the growing season is not unusual, but it is too late to prune at that point (you would lose out on next year's flowers, because you would be removing the flower buds). Prune out dead branches as you find them. Old plants in need of rejuvenation pruning may be cut down to ground level. Japanese rose spreads by suckering; remove suckers as they occur if you wish to control its spread. In fact, the main problem with this plant is that it spreads so vigorously (a drawback for those seeking low-maintenance landscaping); stay ahead of it with regular sucker removal.
Uses in the Yard
Their shade tolerance makes Japanese rose bushes effective in woodland gardens. Kerria japonica is not a good choice for a formal hedge, because excessive pruning ruins its beautiful natural shape; but there is no reason the plant could not be used in a looser, informal hedge. Japanese rose makes for a delightful specimen plant in spring. To enjoy the shrubs fully in winter, consider using them in entryway landscaping or as foundation shrubs, where you will not have to traipse through the snow to view them up-close.
Origin, Meaning of the Common, Scientific Names
Besides "Japanese Rose," other common names for Kerria japonica pick up on the fact that it is a member of the rose family. The common name, "Easter Rose" alludes to its early blooming period (during Easter, in some regions).
The flowers' color accounts for the common name, "Yellow Rose of Texas" (with an assist from the song by the same name). Meanwhile, others commonly refer to it simply as "Kerria rose" or "Japanese Kerria."
So much for the common names; let's turn to the meaning behind the scientific name. The genus name, Kerria comes from William Kerr, who brought the plant from the Far East to the West. The specific epithet, japonica alludes to the fact that the plant is native to Japan (it is also native to China). Finally, the cultivar name, 'Pleniflora' translates from the Latin as "full flowered," a reference to its double flowers.
William Kerr was one of the great 19th-century collectors responsible for importing some of the plants from China that many in the West now take for granted. According to the University of Arkansas Extension, Kerr's contribution, besides Kerria japonica, includes heavenly bamboo, Chinese juniper, and tree peony.