Ceanothus spp.
I remember the first time I noticed a Ceanothus aka California lilac shrub. I literally did a double take as I was walking my dogs on a gloomy late winter’s day in the park by my house.
My eye was drawn to this dark green shrub covered in otherworldly blue flowers that seemed to glow in the landscape.
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Only later did I discover that Ceanothus is fast-growing, fixes nitrogen in the soil, and requires hardly any maintenance. I was already a convert when I first saw its impressive display, but all the rest doesn’t hurt, either.
I immediately added a few California lilacs to my yard and at the same time I started noticing them all over the place in gardens and parks. As far as I’m concerned, there can’t be enough Ceanothus out there.
Whether you’re interested in planting a California lilac of your own, or you want to learn how to care for a specimen you already have, that’s what we’ll cover in this guide.
Here’s what’s coming up:
What Is Ceanothus?
Ceanothus are plants in the Ceanothus genus, that’s the easy part. Many species are commonly known as California lilac, but not all plants in this genus are referred to by this moniker.
They are not related to lilacs, though the flowers bear some resemblance.
Stores and growers will often call all plants in the Ceanothus genus Californian or California lilac because many species are native to California, including feltleaf (C. arboreus), Rincon Ridge (C. confusus), hoaryleaf (C. crassifolius), San Diego buckbrush (C. cyaneus), Fresno (C. fresnensis), Santa Barbara (C. impressus), maritime (C. maritimus), hollyleaf (C. purpureus), and blueblossom (C. thyrsiflorus).
Any one of the 50-ish Ceanothus species native to California might just be called California lilac or blueblossom rather than their more specific common names.
There are similar species that are native to eastern North America, but these are generally referred to by different common names.
For example, C. americanus grows on the east coast and is called New Jersey tea. C. herbaceus grows across eastern North America and goes by the name Jersey tea.
In this guide, we’re going to focus on the Ceanothus species, cultivars, and hybrids that grow on the west coast and are collectively referred to as California lilacs. These all look similar and have similar care requirements.
So, what’s to love about these plants?
Ceanothus are perennial woody shrubs, small trees, or ground cover plants grown both for the foliage and blossoms. Most species are evergreen, though some are deciduous.
The plants produce dense clusters of small flowers in shades of white, cream, gray, or various hues of blue and purple. The majority of species have fragrant, honey-scented blossoms.
You can find types that bloom anytime from January through September, though the majority pop out right at the beginning of spring in March.
After the flowers fade, they are followed by green seed pods that eventually mature and dry out to a light brown color. Once they do, the seeds will burst out of the pods and land far and wide.
I love plants that have this method of ballistic seed dispersal – Oxalis and Impatiens species also have this dispersal method and I love to poke the pods and watch them burst. It brings out the kid in me.
The leaves of all Ceanothus species are ovate with three parallel veins, but that’s where the similarities end.
Depending on the species, the plants can have smooth (entire), dentate, serrate, spiny, or undulate foliage. They can be thick or thin, large or small, and smooth or wrinkled.
Those species that grow in dry regions typically have long thorns and spiny leaves.
California lilacs grow in USDA Hardiness Zones 4 to 11, depending on the species or cultivar, in a huge range of environments, from moist sea level spots to dry mountainsides at 9,000 feet above sea level.
As a member of the legume family, Ceanothus fixes nitrogen in the soil, like peas and beans.
Birds, butterflies, bees, and other wildlife rely on these plants and they are considered some of the most important species for wildlife in many areas.
The roots have been used for centuries to make red dye, and natural dye makers continue to use them today.
Cultivation and History
The species in the Ceanothus genus hybridize readily in nature, so there are many variations out there.
They might have flowers of a different color or size, or may have leaves that are larger or smaller than the species, for instance.
There are also some fun hybrids that have been cultivated over the past few decades as more people have begun to appreciate these plants.
California Lilac Propagation
If you live on the west coast, you’ll find California lilacs for sale all over the place, from specialty nurseries to big box stores. Outside of these areas, you’ll have to hunt a bit harder.
Or, if you have access to an existing Ceanothus plant, you can propagate a new one from seeds or via stem cuttings. If you take seeds or cuttings from a wild plant, be sure it’s safe and legal to do so.
I mention “safe” because I have a friend who loves to collect specimens for cultivation while out hiking, and more than once, she has ventured too close to a cliffside, walked through poison oak, or forgot to be aware of her surroundings while hunting for specimens.
Ok, it’s me. I’m the so-called “friend.” Don’t be like me.
You can sometimes purchase seeds, but mostly, you’ll need to harvest them yourself from existing plants. Let’s talk about that first.
From Seed
Seed sowing needs to be planned in advance. Ceanothus seeds should be sown in the spring, but the process needs to be started in the fall for the best chances of success.
You should also keep in mind that it’s highly unlikely that seed-started plants will look exactly like the parent, whether you’re using seeds from a hybrid or a wild plant.
Remember, the plants hybridize readily in nature, so you never know what you’ll end up with.
After the flowers fade in the spring or summer, depending on the species, hard seed pods will start to form in their place. Once these turn brown and are dry, you can harvest them.
Roll the seed heads in your hand to remove them from the pod. They can be stored in a cool, dry location for up to a year before planting.
Germination in California lilac seeds is triggered by heat. The hot summer days and occasional wildfires in California cause the seeds that have landed in the soil to begin the germination process.
At home, we can replicate this by placing the seeds in a bowl and pouring boiling water over them. Let them sit until the water cools and you can handle them. Strain out the seeds.
You don’t have to do the next step, but it will increase germination rates significantly.
After the boiling water treatment, place the seeds in moist peat moss in a sealable bag and toss them in the refrigerator for three months.
You can always identify an avid gardener because their deli drawer or butter shelf is filled with plastic baggies filled with seeds rather than foods.
In the early spring, fill four-inch containers with potting soil, moisten it, and press a few seeds into the surface of the soil in each pot.
Cover with plastic and place under grow lights or on a windowsill that receives at least four hours of light. Keep the soil moist.
Once the seeds germinate, remove the plastic cover and continue to keep the soil moist. Remove all but the strongest seedling from each pot so there is just one plant in each container.
When the young plants have reached about two or three inches tall and have several leaves, harden them off in preparation for transplanting outdoors.
Do this by placing the pot outdoors for one hour on the first day. The next day, add an hour and then bring it back in. Keep doing this for a full week before transplanting as described below.
From Cuttings
If you want to grow a genetic replica of an existing Ceanothus plant, propagation via stem cuttings is the way to go.
Softwood cuttings taken in spring are the easiest to root, but you can also take hardwood cuttings in the fall. Some species only have hardwood, so you’ll have to work with what you have.
Be sure to take your cuttings on a cold day in the early morning and choose plants that look healthy and aren’t stressed.
If the plant has pliable, easily bendable wood, take a six- to eight-inch cutting from the end of the branch and place the cut end in water to keep it moist while you take other cuttings or prepare your pots.
To take a hardwood cutting, select a small stem with multiple lateral shoots that are at least six inches long.
It doesn’t matter how long the main stem is so long as it has several lateral shoots coming out of it.
Choose a healthy-looking lateral shoot that is at least six inches long and cut the main branch a half inch on either side of the lateral growth.
You should be left with a T-shaped cutting.
The reason we do this is because the main stem is comprised of older wood than the laterals and that older growth has more of the hormones necessary to develop new growth than is contained in the lateral stem.
Place this in water as you work.
When you’re ready to plant, remove all but the top two or three leaves, depending on how large the leaves are. For extremely large leaves, you might want to remove all but one and cut that remaining one in half laterally.
Removing the leaves exposes nodes that will send out roots, and it reduces the amount of aboveground growth that the cutting needs to support as it puts its energy into developing roots.
Fill a clean container with perlite or potting soil. Any well-draining, small container will work, whether you use old plastic cups, new four-inch containers, or pre-used six-packs that your summer annuals came in.
The important thing is that they are cleaned with soapy water and sterilized by wiping them with isopropyl alcohol before use.
Make small holes in the potting medium and insert each cutting two to three inches deep, or a quarter of its length.
Cover with plastic to retain moisture as the roots develop. If you use a plastic bag, which is fine, take care to prop it up so it’s not touching the cutting using sticks or chopsticks or something similar. Otherwise, use a cloche or plastic bottle.
Keep the soil moist and set the cuttings either indoors in a spot with bright, indirect light or outdoors in a protected area, though you should bring them indoors if the temperatures drop below 35°F.
Once you see roots coming out of the drainage holes, it’s time to transplant.
Transplanting
Whether you’ve grown your own seedlings or cuttings, or you purchase a starter plant at a nursery, the planting process is the same.
There’s no need to dig and backfill a massive hole. Just dig a hole a bit wider and just as deep as the existing container the plant is growing in. Remove the plant from the pot and loosen up the roots if they’ve become a bit tangled.
Set the plant in the hole and fill in around the roots. Water well and add more soil if it settles.
How to Grow Ceanothus
Not everyone is lucky enough to be able to grow California lilacs. They need cool summers and mild winters like that of their native coastal California and southern Oregon home.
But even those without the perfect climate can be successful, but there is one thing that is absolutely essential: good drainage.
If your soil doesn’t drain well, I beg you not to grow Ceanothus. They won’t survive.
Assuming you have well-draining soil, the next consideration is sun.
Most Ceanothus species do best in full sun and that’s where you’ll see the best flowering. But in hot regions, the plant will benefit from some shade in the hottest part of the afternoon.
This is especially true of species that are found growing wild along the coast rather than inland. Inland types can tolerate afternoon heat.
Many are extremely drought tolerant, requiring little to no additional water.
In the fall, winter, and spring, nature usually provides enough moisture, but if the soil completely dries out, go ahead and add a little water. In the summer, don’t add moisture at all.
Most Ceanothus species are adapted to thrive in completely dry summers, and added moisture will actually harm them.
Some species need a bit more moisture and this will be noted on the growing card. In these cases, they might need supplemental water in the heat of summer when the soil dries out completely.
Species that grow indigenously along the coast need more water than those that are found inland.
Overwatering is far worse than underwatering.
Don’t bother feeding your California lilac, either. Remember, these plants fix nitrogen in the soil, so if you add fertilizer that contains nitrogen, you’re just adding nitrogen on top of nitrogen.
On top of that, they’re adapted to grow in depleted soils. Anything sandy, loamy, or rocky will do, provided it drains well and has a pH between 5.5 and 8.5.
The moral of the story is that this plant does best when you neglect it.
You’ll sometimes see Ceanothus described as short-lived, but it doesn’t have to be. Those that are overwatered, overfed, or grown in too much shade will have a short lifespan, but well-cared-for plants can live 15 years or more.
Growing Tips
- Plant in full sun, though some need protection from the afternoon heat.
- Ensure that soil has excellent drainage.
- Most require no additional irrigation, especially in the summer.
Pruning and Maintenance
California lilacs don’t like being pruned or moved, and I can tell you this from experience.
I’ve started several from cuttings and had them growing well in the garden. But when I moved homes and tried to take the plants with me, they died a month or so after transplanting.
Once the plants are in place, do your best not to move them. If you must, do it on a cool day in the spring and try to take as much of the root system as you can.
When it comes to pruning, try to avoid trimming as much as you can. Of course, you should always remove dead, diseased, deformed, or dying branches whenever you see them.
Otherwise, keep in mind that woody species only produce growth on the ends of branches. If you cut back into old wood, the branch won’t send out any new growth, and you’ll be left with a dead stump.
Remove spent growth on the interior of the plant and snip off any lower limbs that drag on the ground.
Species and Cultivars to Select
A few decades ago, you were lucky if you could find one or two different Ceanothus types available in specialty nurseries.
But gardeners have started to really appreciate these gorgeous shrubs, and as such, there are more options than ever before.
Blueblossom
All California lilacs might be referred to as “blueblossom,” but C. thyrsiflorus is the species generally given this common name.
Blueblossom or blue blossom holds a special place in my heart because it’s indigenous to my region, Oregon, and I have one growing in the hell strip in my yard.
It grows large, up to 20 feet tall and wide, producing vivid blue-purple blossoms from mid-spring through early summer in Zones 5 to 9.
When it’s in bloom, the entire plant is so densely robed in blossoms that you can barely even spot the stems and leaves underneath. You have to see it to believe it.
Give this Ceanothus species some shade in the afternoon if you live somewhere with hot summers – and watch the pollinators have a field day.
Centennial
The dark blue flowers of low-growing ‘Centennial’ make for a carpet of color in the spring and again in the summer.
The rest of the time, the plant is blanketed in dark green, glossy leaves. It grows about 12 inches tall and spreads up to eight feet, so one plant can tackle a large area.
It even blooms well in part shade in Zones 7 to 9. Though ‘Centennial’ doesn’t do well in hot climates, it’s more heat tolerant than many of its relatives.
‘Centennial’ is a naturally occurring hybrid between C. foliosos and C. thyrsiflorus var. griseus that breeders have cultivated to create a perfect evergreen ground cover plant.
Concha
‘Concha’ was one of the first Ceanothus cultivars to hit the market in the US.
It started as a naturally occurring hybrid between C. impressus and C. papillosus var. roweanus, and features reddish purple buds that open into blue blossoms in late spring on an eight-foot-tall, 12-foot-wide bush. It grows a bit smaller in warmer climates.
‘Concha’
It was first introduced in 1946 and has remained popular for its ability to withstand poor soil, salt, alkaline soil, and full sun even in the heat. It’s also adaptable to varying moisture levels.
You can find ‘Concha’ available at Nature Hills Nursery in #1 containers.
Dark Star
This is the shrub that knocked my socks off and introduced me to the Ceanothus genus.
‘Dark Star’ has striking royal blue blossoms that smother the eight-foot-tall bush from late winter through early spring.
The fragrant flowers are held above nearly black leaves that have a crinkled texture.
The plant has a compact pyramidal shape and is hardy in Zones 7 to 10.
Introduced in 1971 by Ken Taylor who discovered the seedling in his garden in Aroma, California, this hybrid of C. x impressus and C. papillosus var. roweanus won the Royal Horticultural Society’s Award of Garden Merit in 2002.
Joyce Coulter
For a low-growing hedge option, ‘Joyce Coulter’ is an excellent choice. It grows up to four feet tall and ten feet wide, though it can vary in either direction by a few feet.
It’s a hybrid of C. papillosus var. roweanus and likely C. impressus (or maybe C. thyrsiflorus var. griseus), discovered by breeder John E. Coulter, who named it for his wife, and introduced by the Saratoga Horticultural Foundation in 1956.
‘Joyce Coulter’ is extremely tolerant of just about any soil type you can toss at it, from clay to sand, and even a bit of salt. It’s also drought-tolerant.
‘Joyce Coulter’
This prolific bloomer produces medium blue, heavily fragrant flower spikes and will tolerate pruning better than many others.
You can find ‘Joyce Coulter’ available from Fast Growing Trees.
Marie Bleu
Marie Bleu is a cross between C. herbaceus and C. × delilianus, often listed as C. × pallidus ‘Minmari.’
It’s semi-evergreen and perfectly petite at four feet tall and three feet wide. Covered in pale blue flowers in the summer, the red seed heads that follow extend the show in Zones 6 to 9.
The rounded, neat plant is perfect for rock gardens or low borders along a walkway.
Combine it with drought-loving grasses like fountain grass (Pennisetum) or cotton candy grass (Muhlenbergia capillaris).
Point Reyes
Guess where this California lilac grows? Endemic to the Point Reyes area near San Francisco, C. gloriosus has a spreading habit that grows up to six feet wide and three feet tall.
It grows well in Zones 7 to 10.
‘Port Reyes’
This species is extremely popular as a ground cover thanks to its dense growth, glossy green leaves, pinkish-red buds, and the lilac-to-deep-blue flowers that carpet the plant all spring.
Nature Hills carries this Ceanothus species in #1 containers if it sounds perfect for your space.
Ray Hartman
One of the larger Ceanothus cultivars, growing up to 20 feet tall and wide, ‘Ray Hartman’ wows not only with its size but with the rose-colored buds followed by deep blue-violet blossoms.
With careful pruning when it’s young, you can train this cultivar into a tree shape for an even more dramatic focal point.
This hybrid between C. arboreus and C. griseus, created by breeder and founder of the Saratoga Horticultural Foundation Ray Hartman in the 1940s, is extremely adaptable and will even tolerate a bit of clay, as well as some overwatering, drought, and full sun, even in hot regions.
‘Ray Hartman’
It’s suitable for cultivation in Zones 9 and 10.
You can find ‘Ray Hartman’ available at Nature Hills in #1 containers.
Skylark
This C. thyrsiflorus and C. velutinus hybrid grows up to four feet tall and six feet wide, making it a nice option for a smaller area.
It tolerates partial shade and needs no additional irrigation, even in dry climates.
‘Skylark’
The deep blue blossoms that appear in spring and again in the fall make it truly worthy of the Royal Horticultural Society’s Award of Garden Merit, which it nabbed in 2002.
And it doesn’t just produce a few handful of blossoms, the shrub is absolutely blanketed in them.
Nature Hills has this floriferous fantasy in #5 containers for those living in Zones 7 to 10.
Victoria
C. impressus ‘Victoria’ is one of the most popular plants in the genus, and there’s no question why.
The glossy green leaves on the ten-foot-tall and wide shrub are striking on their own, but when the indigo purple flowers join them in the late spring, it makes for quite the show in Zones 7 to 10.
‘Victoria’
‘Victoria’ is also one of the more adaptable options, it tolerates pruning well enough that you can shape it into a hedge and trim it each year.
Visit Nature Hills Nursery to find one for your garden.
Yankee Point
C. thyrsiflorus var. griseus ‘Yankee Point’ is extremely popular as a low-growing option.
It grows about three feet tall and ten feet wide at most, though it might grow taller if you limit its width through pruning.
The sapphire blue flowers explode like fireworks all over the bush starting in mid-spring and last through early summer.
‘Yankee Point’
‘Yankee Point’ is highly drought tolerant but it’s not comfortable in colder climates. Hardy in Zones 8 to 11.
You can find ‘Yankee Point’ plants available from Fast Growing Trees.
Managing Pests and Disease
So long as you don’t plant in poorly draining soil or overwater the plants, Ceanothus have pretty much no problems at all.
In waterlogged soil, the California lilac might not die immediately, but its lifespan will be shortened.
You will sometimes see California lilacs described as deer-resistant. I think that comes from the fact that some Ceanothus species have long thorns and spiky leaves.
These plants developed their sharp bits specifically to deter deer, and these types are certainly deer-resistant.
But the spiky species are rarely cultivated in home gardens. Those you find at plant nurseries are typically the coastal species that lack spikes and thorns.
Deer love these, and they rely on them as a source of protein and calcium, particularly in the winter.
In the case of a larger plant, a bit of feeding isn’t usually too much of a problem, but young specimens can be destroyed overnight.
Cage or fence off young plants until they are large enough to withstand browsing. Most reach their mature size within five years.
Oystershell scale (Lepidosaphes ulmi) will take advantage of stressed plants, and if the numbers of these sapsuckers build up enough, the branches and leaves can turn yellow or brown.
Healthy plants are usually fine, but if you find your plant has an infestation, take a day to scrape off all the scale you can find and drown them in soapy water. Do this every day for a week.
Learn more about how to manage scale in our guide.
The plants in the Ceanothus genus are susceptible to Armillaria mellea fungus, particularly those grown in poorly-draining soil or those that are overwatered.
If you see brown mushrooms clustered at the base of the California lilac, it’s entirely possible your plant is infected.
There are no effective cures for honey fungus, as this disease is also known, so avoid infection by planting in well-draining soil and taking care never to overwater.
Best Uses for California Lilac
Depending on which species or cultivar you’re growing, Ceanothus is ideal as a ground cover, in mass planting, as a hedge, a specimen, in borders, or as a background plant.
There are even a few that you can train into a tree shape if that interests you.
If you’re looking for good companions for your California lilac plants, consider ornamental grasses, lamb’s ears, lavender, sage, and sedum.
Quick Reference Growing Guide
| Plant Type: | Woody flowering shrub | Flower/Foliage Color: | Blue, pink, purple, white / green |
| Native to: | North America | Maintenance: | Low |
| Hardiness (USDA Zones): | 4-11 | Tolerance | Drought, salt, sand |
| Bloom Time: | Winter, spring, summer, depending on species | Soil Type: | Sandy, rocky, loose, loamy |
| Exposure: | Full sun | Soil pH: | 5.5-8.5 |
| Time to Maturity: | 5 years | Soil Drainage: | Well-draining |
| Spacing: | feet, depending on variety | Attracts: | Pollinators, deer |
| Planting Depth: | Surface sow (seeds), same depth as growing container (transplants) | Companion Planting: | Grasses, lamb’s ears, lavender, sage, sedum |
| Height: | Up to 20 feet | Uses: | Ground cover, mass planting, hedge, specimen, borders |
| Spread: | Up to 20 feet | Order: | Rosales |
| Growth Rate: | Fast | Family: | Rhamnaceae |
| Water Needs: | Low | Genus: | Ceanothus |
| Common Pests and Diseases: | Deer, scale; armillaria | Species: | Arboreus, confusus, crassifolius, cyaneus, foliosos, fresnensis, herbaceus, impressus, maritimus, papillosus, purpureus, thyrsiflorus, velutinus |
Lilacs Ain’t Got Nothing on Ceanothus
California lilacs give more than they take.
They add nitrogen to the soil rather than taking it out, give you a dramatic floral show without any pruning required, and they attract pollinators to the yard.
All without any fussing on your part.
Are you growing California lilacs? Let us know in the comments section below!
And for more information about growing shrubs in your garden, have a read of these guides next:
