Let’s just get this out of the way before you think to make the observation–it is just a coincidence that the subjects of today’s post both have blue flowers! Most west coast gardeners are very familiar with the sprawling shrub commonly called Cape Plumbago, botanical name Plumbago auriculata or Plumbago capensis depending on your reference material. It is a staple of freeway landscaping in Southern California where the temperate climate encourages it to bloom year round. Far fewer gardeners have made friends with its cousin Ceratostigma plumbaginoides, commonly called Dwarf Plumbago. Here’s a peek at both!
Cape plumbago comes to us by way of South Africa and has earned its place in the record books as a workhorse shrub which is not too fussy about its conditions. My south Orange County, CA garden had several hundred feet of very steeply sloped ground, much of which was planted in this beautiful shrub. A single plant will grow into a loose mound 6 feet tall and 8-10′ wide making it a good choice to cover large banks or open areas. If you need to keep it more under control just prune it back a bit in late winter. I have room in my Central Valley garden for only the single plant you see in the photo. It performs beautifully and fulfills the thankless function of covering a good bit of ground in the foreground of an established olive tree–ground which is almost untillable and an area of intense competition for water. Cape plumbago will be evergreen in areas of little frost. True to its South African origins, frost will burn new growth and reduce your plant to a blackened mess but the shrub generally has good prospects for a spring recovery. Cold tolerance is not a sure thing below USDA Zone 7 or 8. Recently I learned that seedlings of this plant vary widely in the intensity of the blue phlox type flowers. Mine is a very pale blue. If you want to be sure of a more sky blue try to either purchase one of the named varieties such as ‘Imperial Blue’ or choose your plant when it is in bloom.
You simply cannot find many plants bearing blue flowers as intense as those Ceratostigma plumbaginoides sports. This shrubby wirey-stemmed ground cover is treated as a perennial in most areas. In my garden it breaks dormancy very late (June) and requires a long growing season to come into bloom, usually in late summer when the cool blue is a welcome sight in an otherwise parched landscape. Dwarf plumbago spreads by underground stems and it is purported to grow rapidly and widely in loose soil. My colonies are a bit more restrained perhaps due to limited water and more compact soil than it prefers. The fresh green foliage carpets (maybe more like an throw rug than a carpet!) areas beneath a grouping of miniature roses and a few clumps of under-performing daylilies. By the time the blooms are at their peak the foliage will be starting to redden for fall, providing additional contrast. In my garden the foliage dies back for the winter. When late spring arrives I shear anything remaining above ground to stimulate the new bright green growth.
Temperate winter gardeners like myself have a tendency to dismiss deciduous plant material. Because our landscapes do not spend the cold months buried under ice, snow or slush we seem to believe we are entitled to gardens that are green and blooming all the time, thus we gravitate toward evergreen trees and shrubs and ground covers (not to mention winter ryegrass and the flats of winter annuals!) Because we don’t put our gardens to bed for the winter in the same way that many midwest and northeast gardeners do we also do not get to experience the thrill of the first crocus peeking up through the snow and many other early spring delights. I can’t help but feel that the deciduous nature of the dwarf plumbago has been the deciding factor in its underuse in mild winter gardens.
I challenge you to expand your garden’s horizon with one new deciduous perennial, ground cover or shrub this fall–maybe the dwarf plumbago is the one for you! Dig it in, kiss it goodbye for the winter and wait for the rewards of spring.