Kerria japonica Pleniflora is a double-petalled variety of a Chinese shrub. Kerria is a rangy undisciplined plant that has the tendency to sucker and spread. The oval green leaves are dull and have noticeable ridges and flank the bright yellow flowers. The plant is easy to cultivate with no special needs and a volunteer sprouting habit. Kerria japonica Pleniflora needs late spring pruning to keep it looking attractive. The bush flowers off new growth, which means you can cut it all the way down if you do it early enough and allow it to form new growth to carry the blooms.
Plant Japanese kerria in humic-rich soil. To provide organic amendment, dig in 3 to 5 inches of compost in a 2-square-foot area. Remove all weeds within three feet of the area where you plant the kerria. Chose either a full sun or partial shade location, though the blossoms fade in full sun exposure.
Prune the kerria after it flowers. Prune out the flowering stems as they are finished or cut out the old shoots. You can be quite brutal with the plant and even cut it all the way to the ground. Use well-sharpened pruning tools to make clean cuts.
Remove the suckers at any time of the year. Kerria japonica Pleniflora produces these constantly and they make the plant look rangy if not removed. The plant looks very ragged if it is not pruned annually.
Water the plant only when the weather is extremely warm. Plants in full sun need to be watered more often than those in semishady locations. Irrigate until the soil feels damp in the first 3 inches. Allow the soil to completely dry out before watering again.
Spread 3 to 4 inches of mulch around the base of the plant. Leave at least 1/4 inch near the stems without mulch to allow air circulation. Piling the mulch up around the stems can cause them to rot. The mulch conserves moisture and prevents weeds.