Ceratostigma — Chinese and Burmese Plumbago
It’s hard to find a blue-flowering perennial that blooms for most of the summer, requires minimal maintenance, looks good year round, does not appeal to deer, and is heat and drought tolerant. Most flowers described as blue turn out to be purple, and most plants with true blue flowers bloom only during spring or thrive only in shade.
But for a breath of blue in the garden on a hot summer’s day, nothing cools off the landscape like Ceratostigma. It is one of the few blue, summer-flowering species completely adaptable to Sonoma County’s Mediterranean climate.
Ceratostigma’s striking bright blue blossoms are large enough and occur in great enough quantities to make these plants a colorful addition to gardens. Their size is significant since they can be seen easily enough at a distance to have a striking impact. Smaller blooms, especially blues, tend to “gray out” if planted too far away.
Another appealing feature is their attractive green foliage with thin, reddish margins lined with tiny, fringe-like pale hairs. True blue flowers and bright green leaves are not common in drought-tolerant plants where gray is more the norm. Surprisingly, despite their refreshing look, ceratostigmas never flinch in the heat nor are bothered by inconsistent watering.
These plants are even attractive when they’re not blooming. As temperatures drop in the fall, their leaves make a beautiful colorful display as they turn vibrant red before dropping with frost and rains.
Maintenance requirements are minimal. Unlike many perennials, no dead-heading is needed and plants can be ignored all summer.
Known as Chinese plumbago, Ceratostigma willmottianum starts blooming in early summer and keeps its flowers until fall. Diamond-shaped leaves are held on wiry stems that fan out gently, forming a delicate clump and giving the plant an airy look that belies its toughness. Each leaf hangs distinctly and is curved slightly to show off its bright green color.
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 or dug up.
When planting the Ceratostigma willmottianum, give it plenty of room. It grows 3-4 ft. tall by 4-5 ft. wide and looks best when not crowded and given occasional water. 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.
Another ceratostigma, C. griffithii (Burmese plumbago) is somewhat similar to C. willmottianum, but has rounder leaves, flowers a little later, is sturdier looking with denser branching, and lacks the airy look of its cousin. It may be planted alone or sheared into a low hedge. Its foliage turns the same attractive red in fall, and like other ceratostigmas, it is drought tolerant.
A much different species, Ceratostigma plumbaginoides hugs the ground and, over time, forms a mat 6-12 in. high with thin, wiry stems and vivid blue flowers. In loose soils it can increase rapidly via underground stems and is best used in a contained area or where it has ample room to spread over time. In full sun or light shade, foliage develops riveting fall colors before dying back when it can be sheared low to the ground.
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 rather than in cooler northern California—with the botanical name Plumbago auriculata. It is an entirely different plant that is vine-like and fairly frost tender.