It is important to prune Kerrias just after flowering in late Spring. The flowered shoots are simply cut back, allowing the new growth to ripen for next year's flower crop. It must be done right after flowering - certainly by mid-June for best effect.
Kerria japonica Flore plene, and Pleniflora, together with the variegated kerria Picta pr Variegatum are deciduous shrubs that flower early in the year on growth made in the previous year.
Kerrias can be pruned quite hard after flowering - in spring. They send growth up from the base, and this should be encouraged by the pruning shown above.
Cut back all of the flowered shoots to side shoots or strong buds well down the shrub. Do this right after flowering in order to give next year's flowering shoots plenty of time to develop and ripen.
Every few years or so, the whole shrub can be pruned back to just above ground level - making sure not to cut the new growths that will be emerging from ground level.
This way, you will get a good show of bright green canes in the Winter, followed by the flowers in late Spring.
Kerria japonica is a late spring flowering shrubs with yellow flowers. It has moderate growth to full size of around 6-7ft – (1.8 – 2m) height and spread when mature over 5-6 years. There are a few different types – each having a different habit of growth which will be described below.
The moderate growth and several seasons of interest make the Kerria a good starting point into shrub gardening. As well as the masses of yellow flowers - which can be single or double depending upon your choice of variety - they also have attractive bright green foliage, and bright green stems through the dull winter months. Almost a case of buy one, get two others free.
Kerria japonica is trouble free – having no pests or diseases to worry about. Together with that, they will grow in virtually any garden soil – preferably moist, but will also tolerate dry areas. Kerria can be planted in full sun or partial shade. The best I have seen was growing in the shade of a neighbor’s C. leylandii hedge – never failing to brighten up the dark corner.
Any garden situation will be suitable – either full sun, or woodland shade. It prefers moist conditions, but if occasionally watered in drought conditions, will be suited in drier spots. The single flowered types blend in better in a woodland situation rather than the slightly more formal growth hapit of K. j ‘Pleniflora’
All of the Kerrias tend to form a thicket of branches from ground level.
They are all fully hardy, and do not suffer frost or wind damage.
Kerria japonica ‘Pleniflora’ is the most widely grow of the small Kerria group. It has golden yellow pom-pom flowers in early spring, but also has a few flowers throughout the summer. This variety is upright growing with erect bright green ‘canes’ from the ground-level clump. It is very prolific, and has showy double flowers, which are 2.5-3cm across.
The foliage is bright green with attractive deeply serrated spearhead-shaped leaves. The foliage is attractive through the summer and does not lose its bright green colour. If pruned well right after flowering, it will send up new shoots which will develop into bright apple-green canes, which are attractive in the winter months.
1.8m high with similar spread.
Kerria japonica Golden Guinea has bowl shaped single flowers - but larger than the double flowered version, being 3 - 3.5cm across. Again being prolific. It has more of a spreading habit of growth than the ‘Pleniflora’ – somewhat untidy with wiry stems spreading outwards from the basal clump.
It’s final height is not normally any higher then 1.4 – with a similar spread.
Kerria japonica ‘Picta’ or Variegata – is similar in habit to the Golden Guinea, but with silver splashed variegations to foliage. The gold flowers backed by the silvered leaved add an interesting contrast.