by Sonoma County Master Gardener Lyn Gannon
WANTED: Blue flowering perennial for sunny conditions. Must bloom for most of the summer, require minimal maintenance, and look good year round. Cannot appeal to deer. Only heat and drought tolerant candidates need apply!
Their bright blue flowers make these plants make a colorful addition to my garden. Besides their striking color, the flowers are large enough and occur in great enough quantities to be seen at a distance. This is significant because small blooms (especially pastels) tend to “gray out” if planted too far away. In contrast, larger flowers have a bigger impact. Many times I’ve bought a plant because the bloom has caught my eye when I saw it up close, but I’ve been disappointed when it’s been lost in the landscape.
Another appealing feature of ceratostigmas is their bright green foliage. Like true blue flowers, bright green leaves are not common in drought-tolerant plants. Gray is more the norm. While I sprinkle gray-foliaged plants throughout my garden, I also like the liveliness of bright green, which is where Ceratostigma come in handy. Surprisingly, despite their refreshing look, they never flinch in the heat and they handle inconsistent water.
These plants are even attractive when they’re not blooming. When temperatures drop in the fall, their leaves make a beautiful display. Many drought tolerant plants disappear or look ragged at this time of year. Not ceratostigmas! Their leaves turn a vibrant red, and then drop with the frost and rains.
Despite their attractive foliage, deer seem to shun ceratostigmas. What a relief to find a deer-resistant plant that doesn’t look it’s made of armor! I like my garden to look juicy in the summer. But I live with deer, so I have to choose my plants carefully. In our neighborhood, I’ve seen many gardens ravaged by deer, but the ceratostigmas are unscathed.
Lastly, ceratostigmas’ maintenance requirements are minimal. Unlike many perennials, they don’t require frequent dead-heading. In fact, I don’t touch mine all summer. Yet day after day, they look great.
Ceratostigma willmottianum
Of the taller versions, I prefer the ceratostigma willmottianum – otherwise known as Chinese Plumbago. Willmottianums start blooming in early summer and keep their flowers until fall. The diamond shaped leaves are held on wiry stems, which give the plant an airy look and belie their toughness. The leaves are not just a clump of green, either. Each leaf hangs distinctly and is curved slightly to show off its bright green color.
Their wiry stems fan out gently, forming a delicate clump. But those stems are strong! So willmottianums don’t need staking – another big asset. They are one of the few perennials which can hold themselves upright enough to look good on flat ground. Yet their stems are flexible enough to spill gently down a slope. Very few plants have such an adaptable habit.
Even leafless, willmottianums’ wiry stems look attractive when silhouetted against the winter sky. In the early spring, you can thin out some of the branches. That way you won’t end up with a thicket. Or, you can simply cut the plant to the ground, which is what I do – much simpler! They generate new growth rapidly.
When you plant the willmottianums, give them plenty of room. They grow about 4’ tall and around 5’ wide. And, they look best when not crowded so you can appreciate their shape. They will look better with occasional water, but I’m surprised to see many volunteers thriving in places where there is no irrigation.
By the way, if you don’t want volunteers, remove the seeds heads before they mature. Either snip the flowers off after they fade, or clip the seed heads before they crumple in your fingers. The latter sign indicates that the seeds are mature and ready to drop.
Another form of ceratostigma which looks very similar to willmottianum is C. griffithii, or Burmese Plumbago. The key difference between the two is that this one is smaller – about 3’ X 3’. This size can be more manageable in smaller gardens.
This plant has a slightly different shape, too. It is sturdier looking and doesn’t have quite the airy look of its cousin, the willmottianum. It is a plant that would make a good small hedge, which is a useful shape to have in the garden.
Griffithii have rounder leaves and flower a little later. This can be their one disadvantage because their blooms can be halted by the frost. Still, they sport the same bright blue flowers and spritely green foliage characteristic of ceratostigmas. Their foliage turns the same attractive red in the fall. And like other ceratostigmas, griffithii is drought tolerant.
Ceratostigma plumbaginoides
If you’re looking for a ground cover then consider Ceratostigma plumbaginoides. This species hugs the ground and over time, forms a mat about 6-12” high. Like other ceratostigmas, they have bright blue flowers. They are also deciduous, drought tolerant and have red leaves in the fall.
They are tough little plants. They spread via underground stems, and in loose soils they can spread rapidly. Some are growing at my house over a gravel drain! I’ve dug up them up to transplant several times. In each case, I thought I I’d removed all the roots, but the patch has continued to return, and each year gets a little larger, despite no nearby irrigation. This plant is best used in a contained area or in a spot where it has ample room to spread over time.
Plumbaginoides tends to bloom a little later in the summer. Mine just started blooming in August. I’ve found that they do well in light shade. Again, their bright blue color lights up the garden, especially at this time of year.
Since they don’t have significant stems, plumbaginoides can disappear during the winter months. Don’t be fooled – you didn’t kill them. Shear what’s left in the early spring, and as the days warm, the leaves will re-appear.
Next time you are time you’re looking for a tough plant that can liven up your garden, I hope you will give ceratostigma a try. Few perennials offer so many features and yet are so trouble free. They have the fresh look of spring and still allow you to water sparingly. I guarantee you won’t be disappointed!
NOTE: One 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 - often seen in Southern California - with the botanical name plumbago aurticulata. It is an entirely different plant.
©Sonoma County Master Gardeners