Horticulture Magazine

Ceanothus ‘California Lilac’ Care & Growing Tips

blooming purple Californian lilac flowers

Ceanothus Overview

Official Plant NameCeanothus
Common Name(s)Californian Lilac
Plant TypeShrub
Native AreaUnited States
Hardiness RatingH4
ToxicityNone
FoliageEvergreen
FlowersSmall blue, white or pink flowers in terminal clusters
When To SowMarch, April, May
Flowering MonthsJune, July, August, September, October
When To PruneAugust, September
Sunlight

Preferred
Full Sun

Exposure
Sheltered

Size

Height
1.5 – 2.5M

Spread
2.5 – 4M

Bloom Time
Spring, summer and autumn flowering types

Soil

Preferred
Chalk, loam, sand

Moisture
Well drained

pH
Any

Break down the Greek word that gave rise to the name of this plant, and you’ll find it translates to “spiny plant” – a label that sidesteps the truly defining characteristics of the flower: Big bushels of colourful florets, which bring bold bursts of beauty to any garden.

If you’re looking for an attractive and versatile plant, then look no further. Ceanothus has varieties that flower in spring, summer, and autumn. It has a range of colours to match any palette, and the flower itself is suited to hedges, ground cover, or even as a source of scent in your garden.

a ceanothus hedge in a garden
Spiny isn’t the first word that comes to mind!

In this guide we’ll introduce a few popular varieties of ceanothus, and get you acquainted with the information you need to get them thriving in your garden.

What is Ceanothus?

As we said earlier, the name means “spiny plant”. You’ll also see common names used, including soap bush, California lilac (alluding to the west coast of America, where this plant is most diverse), and buckbrush.

The genus contains about 60 species of plant, ranging in size from shrubs to small trees. Originally hailing from North America, from coastal areas to mountaintops, ceanothus has become a popular candidate for British gardens thanks to its versatility and beauty.

close up of a bee sat on blue california lilac
It’s a real hit with bees, too

Types of Ceanothus

There are myriad plants in the ceanothus family, fourteen of which have received the Royal Horticultural Society’s Award of Garden Merit, indicating that they’re very well suited to growing in British gardens. Below, we’ll introduce a few varieties that have received this award. If you’re planning to grow ceanothus in your garden, you’d do well to consider these varieties firsts.

Ceanothus ‘Autumnal Blue’

Fronds of light blue, almost white flowers branch off from a vibrant green stem, giving this variety a delicate appeal. The RHS recommends planting autumnal blue in wall-side borders to take full advantage of its height and spread.

This variety enjoys full sun, moist but well-drained soil, and alkaline or neutral pH levels.

Ceanothus thyrsiflorus ‘Mystery Blue’

This variety also boasts blue, almost purple flowers that burst forth in spring and summer – slightly earlier flowering than autumnal blue, which is in full bloom during summer and autumn. This relationship demonstrates the staggered flowering patterns that can be utilised to create visually interesting displays.

The mystery blue enjoys the same conditions as autumnal blue, but can tolerate lightly acidic soil

Ceanothus x pallidus ‘Perle Rose’

The white-pink flowers perched at the end of pretty pink stems are a perfect showcase of the variety of colours represented in the ceanothus family. Whether used to contrast against a blue variety, or paired with another pink white bloom, perle rose is an attractive and rewarding choice. You’ll be able to enjoy full bloom in summer.

Preferred conditions are similar to those of the autumnal blue.

Ceanothus thyrsiflorus var. repens ‘Creeping blue blossom’

The vibrant blue flowers of this ceanothus variety are a sight to behold, and bring a depth of blue that not many others can achieve. The bushy aesthetic and bold colour palette, leaping into full bloom in summer and spring, reward persistent gardeners with a truly eye-catching floral display.

This variety prefers sheltered exposure, but is otherwise similar to the mystery blue.

Why grow Ceanothus?

This family of plants includes a huge spectrum of colours, and offers enough variety in preferred growing conditions that most gardeners will be able to find at least something compatible with their outdoor space. What’s more, the majority of ceanothus are rated as having hardiness of H4 or below, meaning they can thrive in temperatures down to -5 degrees – great for most of Britain.

How to grow

The growing and care tips given below are indicative of some plants in the family, but not all of them. With so many varieties available, we recommend checking the specific requirements of each and every ceanothus you decide to grow.

Where to grow

Hailing from the West coast of America, this plant can tolerate a lot of sunlight. For best growth, plant somewhere with full sun exposure, and with a little shelter against the harsher winds and frosts they’ll experience in Britain. Somewhere facing west or south should do the trick.

In terms of soil, the general rule is most but well-drained, with neutral or alkali pH level. Some varieties can tolerate acidity, but as we said earlier, double check the specific varieties you’re planning to grow to avoid disappointment.

How to plant

Plant in spring to avoid damage, unless you have particularly well-draining soil, in which case you can safely plant in autumn. Digging in leaf mould or manure aids with drainage, and increases the chance of ceanothus taking.

Fertilising

Ceanothus doesn’t require feeding, but will benefit if you decide to do it. Sprinkle a little fertiliser around the base, leaving a ring of around 3-5cm from the plant. This helps to avoid rot, which can occur if you fertilise too close to the plant.

Watering

You’ll want to water your ceanothus fairly frequently until the roots are established, which can take a few years. This is especially important during summer and other unseasonably hot periods.

When your ceanothus is established, it won’t need much watering unless you’re experiencing drought conditions.

Pruning & deadheading

As with fertilising, it’s not necessary to deadhead but your plant may enjoy it. Ceanothus has a tendency to become overcrowded, which can stifle future growth and make their visual appearance cluttered. Remove spent blooms or deadhead new growth to keep a healthy appearance.

Pruning depends on the type of ceanothus you’re growing –

  • Varieties that flower in spring and summer should be pruned after flowering. Trim back between 30-50% of the shoot.
  • Varieties that flower in summer should be pruned the following spring. Again, trim between 30-50% of the shoot.

Training your plant

This plant is well-suited to training up walls and other vertical surfaces. Use twine to gently tie new shoots onto supporting structures, like trellises or chicken wire. This should encourage vertical growth without causing damage to the plant.

ceanothus and other shrubs next to a garden wall with a house in the background
How to train your ceanothus

Propagating Ceanothus

You can propagate ceanothus from cuttings, with a child plant being ready to flower about three years after being planted. Cut a few inches of healthy growth from this year’s season, and grow indoors for a season before potting or planting out.

Troubleshooting issues

Ceanothus is fairly free from pests and diseases, making it a forgiving choice for gardeners who don’t have lots of time to spend monitoring the health of their plants. There are a couple of things to keep an eye on, however.

Exposure damage

As we’ve alluded to, this plant’s West Coast origins mean it may not cope so well with some of the harsher conditions the UK throws at it. If you’re not able to find a sheltered location for your ceanothus, try to control against damage from wind and frost.

Wind scorch is caused by cold winds pulling moisture from plants and soil, putting them in a position where they struggle to replace the water quickly enough. As a result, leaf edges – or entire leaves in particularly bad cases – may turn brown. If your ceanothus is growing in an exposed position and strong winds are forecast, do your best to erect a windbreak – either manmade or in the form of another plant. Be careful to ensure the wind can blow through the windbreak: A completely solid surface (like a fence panel, for example), is liable to fall over and damage the plant it’s supposed to protect.

Frost can also cause lots of damage to plants, hurting existing growth and stifling next season’s growth. Though ceanothus is hardy, it will struggle in some UK temperatures. Using horticultural fleece, mulch, or some other insulating medium around the root of the plant can protect against frosty spells, and pruning damaged sections can control the damage caused. Erecting shelters is another way to reduce frost risk.

Scale insects

These pests like to make their home on ceanothus leaves, feasting on the succulent sap contained within. You’ll see bumpy ridges on leaf undersides, and possibly black fungus atop the leaves that grows on the insects’ excretions.

At first you can remove the insects by hand, although this won’t work against higher numbers. You can encourage predators to visit your garden to eat the insects or, failing that, a range of pesticides are available to curb more persistent visitors.

Enjoy your Ceanothus!

After reading this guide you should be confident in choosing the right ceanothus for your garden, and in getting the plant established and thriving. This colourful and striking plant, with its bundles of brightly coloured flowers vying for attention and providing beautiful backdrops for medleys of other flowers, makes a fine addition to any garden. We’re sure you’ll enjoy incorporating them into yours!

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