Plumbago — A True Blue Accent in the Sunny Border
As their name suggests, groundcovers are plants that grow thick and spread to cover the ground. However, the very characteristics that we look for in a groundcover – matting, spreading, or vining — can also make them disagreeable to live with in the ornamental garden. Plumbago (Ceratostigma plumbaginoides) is a spreading plant that embodies many of the best characteristics of a groundcover without resorting to thuggish tendencies. This plant is relatively underused in the Mid-Atlantic states, perhaps because it is deciduous. Gardeners may prefer more popular evergreen groundcovers, such as vinca, pachysandra, and English ivy. Or, perhaps its many common names (leadwort, perennial leadwort, plumbago, hardy plumbago, or dwarf plumbago) confuse the average home gardener. More often than not, it is identified simply as either plumbago or leadwort. As for the origin of the name, it comes from the Latin plumbum, which means lead. The plant was thought to be a cure for lead poisoning, according to the writings of Pliny the Elder in the first century AD. While it may not cure lead poisoning, it does make a very effective groundcover.
Hailing from western China, plumbago is a deciduous, flowering herbaceous perennial with a low-growing, mat-forming habit. It spreads about 12” to 18” wide and grows 6” to 10” tall. In his book Herbaceous Perennial Plants, 3rd Edition, world renowned horticulturist Dr. Allan Armitage describes it as “a terrific species, looking equally as good in Athens, Georgia and Niagara, Ontario.” As further evidence of its value in the landscape, plumbago was recognized as a Georgia Gold Medal Winner for perennials in 2006.
Plumbago foliage is late to appear in spring. When it does sprout, the new 1-1/2” long leaves have a reddish tint that gives way to a medium-textured, glossy, bright green color in summer. One of the benefits of this plant is that the foliage looks fresh all summer long, regardless of the heat and humidity. Then, as temperatures begin to cool, the leaves turn a deep burnished shade of red in autumn.
All too often, plants labeled as blue-flowering turn out to be some shade of lavender blue or even purple. Finding a plant that blooms a clear, unmistakable blue can be a challenge. Plumbago meets that challenge. Its dainty ½ to ¾-inch flowers are an electrifying gentian blue, with a shape and color faintly reminiscent of woodland phlox or vinca. The flowers generally cluster at the ends of slender, erect stems and last from summer, when many other perennials are finished blooming for the season, well into fall. Deep reddish calyces contrast with the intense blue flowers and add additional color in autumn.
Plumbago spreads by rhizomes, but it is not invasive. It’s a moderate spreader in good garden soils. But, like all groundcovers, it does spread and should be watched to make sure it doesn’t venture too far. It is probably best used in a spot where it either has ample room to spread over time or where it can be contained. If it does grow beyond its allotted space in the landscape, it’s easy to spade up, particularly if the soil is moist.
Plumbago prefers average to evenly moist, rich soil. Once it is established, it can tolerate dry soil and does not require any supplemental water beyond normal rainfall. It will not tolerate standing water. It is not fussy about soil type or pH and will thrive in poor soils and difficult sites.
Hardy in USDA zones 5 to 9, plumbago does best in full sun. It does tolerate light shade but tends not to bloom as well in shade as it does in full sun.
Plumbago is a tough, low maintenance plant that requires no shearing or pruning. The flowers are self-cleaning, which means no deadheading is required. The foliage drops off after the first frost and the stems may be left in place over winter. The new foliage will cover the old stems. However, if you prefer a tidier garden, there’s no problem with cutting the old stems back, either in fall or late winter. Because new foliage is late to emerge in spring, some gardeners prefer to leave the old stems in place to mark the spot until new growth appears.
OTHER RELATED PLUMBAGO SPECIES
Don’t confuse the groundcover form of plumbago (C. plumbaginoides) with the shrub form (C. willmottianum or Chinese plumbago), which grows 2 to 3 feet tall and is hardy in zones 7 to 9. Another related shrub form of plumbago (C. griffithii, or Burmese plumbago) is smaller than C. willmottianum, has deep blue flowers, and is hardy in zones 6 to 8.
Also, do not confuse C. plumbaginoides with Plumbago aurticulata, a shrub that is native to South Africa. Commonly referred to as cape plumbago or cape leadwort, it is completely different from the Ceratostigma species. Plumbago aurticulata has lighter blue flowers and is only hardy to zone 8. Often found in garden centers in the mid-Atlantic, it must be treated in this area as an annual or grown in a container and overwintered indoors.
Propagate plumbago by dividing it or taking stem cuttings. Divide in spring before new growth appears. Space the transplants about a foot apart. To promote rapid filling in between transplants, lightly apply a slow-release 12-6-6 fertilizer in the spring and again in the early summer. To propagate using stem cuttings, take 3” to 4” long semi-ripe cuttings during the summer.
PESTS AND DISEASES
Plumbago has no serious disease or insect problems. Despite its attractive green foliage, deer and rabbits don’t eat it, which is huge plus in this area.
RECOMMENDED USE IN THE LANDSCAPE
Groundcovers are used primarily to “knit” the landscape together. With this goal in mind, use plumbago as:
- An edging in the sunny border, spanning the space between ornamental plantings and lawn.
- A mass planting, serving either as a groundcover or under other plants as a “skirt.”
- A graceful filler between stones in rock or alpine gardens.
- An alternative (albeit deciduous) to vinca minor and English ivy, both of which are considered invasive.
- An alternative to wood mulch to suppress weeds, shade the soil surface, and conserve water.
- A camouflage to cover dying bulb foliage in spring. Plumbago foliage emerges in late spring as bulb foliage is dying back.
- A means of controlling erosion on slopes or in rocky areas where not much else will grow.
- A component of a container garden that will gently drape over the side of the container.
- A gentle way to soften the edges of a stone wall. While the plant tends to be upright, the foliage does gently cascade over at the edge of the mass.
Plumbago offers a long bloom time and true blue flowers, which are not commonly found in the landscape. Its colorful fall foliage, drought tolerance, deer resistance and lack of pest and disease problems make it a desirable plant to add to the landscape. If, however, you are a native purist, keep in mind that this plant is not native. It does attract bees and butterflies but not to the extent some of our native plants do.
For more information on groundcovers suggested for Virginia landscapes, see Virginia Cooperative Extension Publication 426-609, “Selecting Landscape Plants: Groundcovers.”
Herbaceous Perennial Plants, A Treatise on their Identification, Culture and Garden Attributes, Third Edition (Armitage, Allan M., 2008)
Latin for Gardeners (Harrison, Lorraine, 2012)
Perennials, The Gardener’s Reference (Carter, Susan; Becker, Carrie; and Lilly, Bob, 2007)
The Well-Tended Perennial Garden, Planting and Pruning Techniques (DiSabato-Aust, Tracy, 2006)
Chicago Botanic Garden Plant Information chicagobotanic.org/plantcollections#plantfinder
Clemson Cooperative Extension Publication HGIC 1180, Perennial Leadwort
Georgia Gold Medal Plant Summary 1994 – 2010, Gold Medal Plant Summary
“Selecting Landscape Plants: Groundcovers,” Virginia Cooperative Extension Publication 426-609