General gardening topics

Growing ceanothus – a beginners guide

Last updated on February 27th, 2022

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This is a large genus of shrubs that are very versatile and beautiful. Many of the shrubs are native to California which is why the plant is colloquially referred to as the California Lilac. Of course, this name is a bit misleading because it is not a lilac at all.

This Ceanothus bush grows between 30 and 180cm tall, and some varieties will grow into a mound shape while others grow prostrate and turn into small trees if you let them.

They can even be used for hedging and will produce a mass of flowers from May onwards.

In spite of the differences between the different Ceanothus varieties, you can easily recognise any of these plants thanks to their distinctive flowers and leaves. The leaves are oval in shape with two stages and each leaf contains three veins that run parallel from the base to the tips. The leaves are glossy and green on top and grow between 1cm and 7cm in length. They typically look like holly leaves but much smaller.

Pink ceanothus shrub

The flowers are often blue but they can be found in different shades. A few varieties will even produce pink or white blossoms. The Ceanothus flowers themselves are very small and they grow in dense clusters and absolutely cover a bush, quite simply, making the most impressive display.

As you walk by you will no doubt smell the intense fragrance they have on offer when they bloom between March and May. Another nickname for this shrub, for the most common variety, is that of the Soap bush. It is called this because it is said that if you mix the flowers with water you can form a lather similar to soap.

Perfect for bees and butterflies

Ceanothus attract bees and are beneficial for insects too
Ceanothus attract bees and are beneficial for insects too

When you plant these bushes you can naturally attract many butterfly species because the plants offer food for butterflies. They also attract other beneficial insects such as bees. If you are growing a habitat garden this is a must.

Propagating ceanothus

These bushes grow in dense fields and they are fairly difficult to germinate so we recommend taking cuttings instead. If you do want to try and grow them from seeds you should collect ripe seeds from a healthy plant or purchase them from a trusted nursery. Store the seeds in an airtight and dry container. If stored correctly, you can keep them for up to 12 years while you prepare your garden for planting but ideally, you want to get them sown as soon as possible after going through the process outlined below.

When you are ready to germinate from seed you should put the seeds through stratification beforehand by placing them in hot water for 5 or 10 seconds and then immediately placing them in cold water, followed by cold stratification for up to three months to mimic the conditions they would receive naturally and then keep at 16-18°C (61-65°F). Germination can take up to three months.

Taking cuttings from ceanothus shrubs

Taking cuttings is usually much easier than growing from seed but it would still be described as moderately difficult. If you want to take a cutting from evergreen varieties then this is best done in late summer to early autumn by taking a semi-ripe cutting.

For deciduous varieties then it’s best to take soft-wood cutting in late spring.

Alternatively, you can purchase a smaller plant from a nursery or garden store and enjoy beautiful blooms much sooner because they often flower even as very small pot-grown plants.

Planting ceanothus

When you are ready to plant, make sure that your Ceanothus is planted in fertile well-drained soil and ideally in full sun. Check the pH levels beforehand because they should be between 6.5 and 8.0, however, if you already have a good mix of plants in your garden then a Ceanothus is likely to thrive too.

Stunning Ceanothus shrub

These plants do well in full sun but will also thrive in partial shade and regardless of their location be sure to give them extra water during the driest parts of summer. You typically don’t need to fertilise these at all and in fact, doing so can be detrimental depending on the type, so we recommend just mulching around the base of plants with compost or well-rotted farm manure in late winter to increase soil fertility and protect the plant from ground frost.

Although they are very hardy in most parts of the UK, they prefer to be planted in a more sheltered spot where they won’t be exposed to cold winds.

Pruning ceanothus

Ceanothus is not a plant that needs pruning but they do benefit from pruning using a good pair of secateurs to encourage them to bush out more and produce more flowers or to simply keep them under control and in shape.

Early flowering Ceanothus thyrsiflorus skylark shrub be pruned after flowering
Early flowering Ceanothus thyrsiflorus skylark shrub be pruned after flowering

When you prune is based on which variety you have because it all depends on when it flowers. If you have an early flowering variety that flowers in late spring to early summer and examples of these include C. impressus and C. thyrsiflorus ‘Skylark’, then these varieties should be pruned straight after flowering, which you can prune by as much as half if needed. They can also benefit from light pruning to tidy them up at the end of the summer.

Ceanothus Autumnal Blue

If you have a later flowering variety such as C. ‘Autumnal Blue’, C. ‘Burkwoodii’ which typically flower in late summer, then we recommend pruning them back by about a third in spring to remove some of the previous years’ growth.

If you have deciduous Ceanothus then we strongly recommend pruning them for the first couple of years in early to mid-spring to encourage a good strong framework. It is recommended that you prune them by as much as two-thirds in the first year and then in the second year prune the previous year’s growth by about two-thirds again. Once fully established, you can prune the main flowering stems by about half and remove any weak growth.

Ceanothus shrubs usually benefit from pruning, however, it’s not essential and many varieties grow well without any pruning at all.

Types of Ceanothus

There are over 50 types of Ceanothus and they range in size from low-growing to medium-sized and even to tree-like sizes, so you can pick the one that best suits your space.

Low-growing shrubs

Low-growing shrubs are best suited for sloped gardens, especially if you want to use them for erosion prevention or as a groundcover shrub. Many of the lower growing shrubs will tolerate more water and shade compared to other varieties.

Ceanothus repens

Ceanothus repens (also known as creeping blue blossom) will grow between 1m to 1.5m high and will typically spread out 3m. This particular variety offers clusters of blue flowers with ovate green leaves and is a small, but vigorous evergreen shrub.

Medium-sized shrubs

Medium-sized shrubs are designed for slightly larger areas. The Julia Phelps variety will grow between 120-180cm tall and spread out between 210 cm and 270 cm. You get dark, indigo coloured flowers with dark green leaves. This particular variety can handle a wide range of environmental conditions.

The Louis Edmonds variety is wider than it is tall so it is better suited for certain garden situations where it is a necessity, especially for those attempting to use the plant as a groundcover. This particular plant will reach heights between 120 and 180cm, and a spread of up to 450cm. The flowers are blue with green leaves.

Tree-like shrubs

The larger varieties take the form of small trees. The Ray Hartmann variety can grow up to 360cm and 540cm tall. It has lavender-blue flowers with dark green leaves. This particular variety will grow very quickly and can grow up to 300cm in only a few years.

Problems that effect ceanothus

Ceanothus do not suffer from many problems, however, they can sometimes be affected by honey fungus and scale insects which should be treated at the first signs. Honey fungus is a fungus that attacks the roots undergrowth causing the plant to die. There is not a chemical cure for this so affected plants are best removed.

Scale insects
scale insects

Scale insects are easy to identify because they have scales and suck the sap from plants and often leave sticky honey due on the leaves. Scale insects can be sprayed with pesticides but it can be ineffective with adults because the waxy scales protects them so the best to time spray in when the nymphs hatch which is usually June to July as their scales are still soft and so spraying with a bug killer is effective for a short period.

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