When to Cut Ceratostigma Plumbaginoides Back?

Pruning Season

The best time to cut back blue leadwort is mid- to late spring, before new leaf growth appears on the naked, sprawling branches. In the northern parts of its hardiness range, pruning may be delayed until mid-May, but farther south the pruning may need to be completed by mid-April to avoid the newly emerging leaves. Do not prune past early summer, as tissues that bear the flowers emerge a few weeks later. Dead stems may be removed at any time.

Blue leadwort plants grow vigorously by spreading rhizome roots underground. Sprouts pop up from the ground to make a thicket of stems. Cut back stems with a lawnmower set at its highest blade setting or with hand-held pruning shears. Make the cuts no closer than 4 inches from the ground on the stems. If plants are sparse or not as vigorous, cut back stems only to 6 to 12 inches -- or approximately 50 to 60 percent less than their original lengths.

To create a fast ground cover, space blue leadwort plants 12 to 18 inches apart. The first two years after planting the growth rate is not overly rapid, but root systems are establishing. The growth of stems as well as underground rhizomes increases in regions with long, warm summers. A crumbly, fertile soil hastens the spread of roots in the garden. In regions with very cold winters in U.S. Department of Agriculture zone 6a and even into zone 5b, plant roots may be killed back, diminishing the spreading tendency of the plant. Lightly mulch the soil over the roots in late fall in these regions to help preserve the roots for plant rejuvenation the next spring.

Blue leadwort grows in any moderately fertile, moist but well-drained soil, including in a rock garden. Lighter-textured soils increase the spread of the plant across the landscape, especially sandy and gritty loam soils enriched with organic matter. Plant blue leadwort in full sun for the best display of flowers toward the end of summer. In hot climates, partial sun with shade in the hottest part of the afternoon is best, as it prevents wilting or bleaching of the blue blossoms.