Ceratostigma (Plumbago or Leadwort)
Commonly called plumbago or leadwort, three of the common Ceratostigma species are evergreen shrubs; the fourth is a groundcover. They are among the few blue summer-flowering shrubs completely adaptable to Sonoma County’s Mediterranean climate.
- These easy-care plants require minimal maintenance and are heat and drought tolerant.
- Small, bright purplish blue blossoms have a striking impact even when viewed from a distance.
- Deep green leaves are outlined with thin, reddish margins lined with tiny, fringe-like pale hairs.
- Ceratostigmas never flinch in heat nor are they bothered by inconsistent watering once established.
- As temperatures drop in autumn, leaves make a colorful display as they turn vibrant colors before dropping with frost and rains.
- Maintenance requirements are minimal—no dead-heading is needed and plants can be ignored all summer.
Choosing a Species
Because all Ceratostigma species slowly spread by underground rhizomes and may also self-sow, it is important to plant them away from natural, wild areas where they cannot be controlled. Volunteer seedlings can appear in places where there is no irrigation. To avoid self-sowing, remove faded flowers or seeds heads before they fully mature.
- Ceratostigma plumbaginoides, a groundcover called dwarf plumbago, spreads more rapidly than shrub members of the genus, a welcome feature for covering open areas. Outstanding fall color is one of the main attractions.
- Some gardeners shy away from this groundcover, however, because it is deciduous in winter when dried stems can be cut to the ground.
- Fast growth in spring is marked by thin, wiry stems rising 6-12 in. tall with 2-3 in. green leaves along the sides. Clusters of phlox-like, blue blossoms at stem tips emerge in summer and last for weeks.
- In full sun or light shade, foliage turns riveting bronze-red for weeks in autumn before dying back.
- In loose soils, spread can increase rapidly via underground stems. Planting is best in a contained area but where there is ample room for spreading over time.
- Ceratostigma willmottianum, Chinese plumbago, also has wiry stems, but these are longer, lankier, and somewhat stouter than those of the groundcover species.
- This 2-4 ft. shrub bears somewhat diamond-shaped leaves, often sparsely, along stems that fan out gently in a lax fashion. They form a delicate mound and give the plant an airy look that belies its toughness. Each leaf hangs distinctly and is curved slightly to show off its bright green color.
- In ideal conditions, Chinese plumbago may grow taller and wider, and rhizomes may require annual removal to control size.
- Blue blossoms begin in early summer and last through fall, in contrast to deep green leaves. Autumn foliage may be yellow, rust, or red before dropping.
- Even leafless, the wiry stems look attractive as they turn rusty brown in winter and may be left standing, or the entire plant may be cut to the ground. It will generate new growth rapidly in spring.
- To manage the shrub’s horizontal spread and avoid a thicket from developing after a number of years, some branches can be pulled out or dug up.
- Ceratostigma minus bears considerable resemblance to willmottianum, but its blossoms are somewhat paler blue. The overall form is also similar but more restrained.
- Ceratostigma griffithii, Burmese plumbago, becomes a sturdier, more densely branched, larger shrub that lacks the airy look of others in the genus.
- It may be planted alone or sheared into a low hedge.
- Leaves are rounder and flowers appear later in the season. Its foliage turns the same attractive red in fall.
- Like other ceratostigmas, it is also drought tolerant.
- Rhizomes account for moderate to rapid spread in loose, moist soil. Withholding irrigation limits spread.
- Watch for self-sown seedlings to appear in unwanted areas, even at a distance from the parent shrub.
A Word of Caution
It’s easy to confuse plants when not using botanical names. Ceratostigmas are a classic example. Their common name is plumbago, but there is also a plant—more often seen in Southern California than in cooler northern coastal areas—with the botanical name Plumbago auriculata. It is an entirely different plant that is completely fairly frost tender, completely vine-like, but is often used as a shrub.