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Tending Kerria in the Garden

How to keep kerria the right size

By: Sandy Feather ©2010
Penn State Extension


Q. I have some lovely kerria plants, both the plain green and the variegated leaf, that need to be reduced in size.  Should I wait until spring and dig around the plants to reduce the size, or cut (not dig) some stems back now?

A. Japanese kerria (Kerria japonica) is a flowering shrub that grows three to six feet tall with a spread of six to ten feet. Kerria is valued for its shade tolerance, long season of bloom, and the bright green stems that hold their color pretty well through the winter. It spreads by sending up shoots from its roots, a growth habit known as suckering. That cute little plant you bought in a gallon container can quickly outgrow its allotted space in the garden.


Getting Started Digging

You can dig out the unwanted suckers now to reduce the overall spread of the plants or wait until spring – your call. Digging out the unwanted suckers is less likely to push new growth at this time of year than pruning. Pruning is better delayed until shrubs and trees are dormant because plants respond to pruning by sending out new growth. At this time of year, that tender growth is likely to be killed by winter cold.

Kerria Japonica

Kerria grows vigorously (hold the fertilizer!) and it is common to find a number of dead stems in the center of overgrown specimens. These can be removed any time you find them. Kerria produces next year’s flower buds as it finishes blooming, known as “blooming on old wood.” If you prune after those buds are set, you will remove next year’s blooms. Although you might miss a year of flowering, it is good practice to rejuvenate kerria periodically by cutting it to the ground in March. When it regains some growth after such treatment, thin the resulting stems to allow for better air circulation and to allow light into the center of the plant.

 

The variegated form (Kerria japonica ‘Picta’) is less vigorous than the all green forms and may not require such drastic pruning. It inevitably produces some plain green shoots that should be removed as soon as you notice them. Since the green stems are more vigorous than the variegated ones, they can quickly take over a variegated plant.

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