ceanothus trewithen blue

Ceanothus, California Lilac

Commonly known as the California lilac it is recognisable by the profusion of lilac blue coloured flowers from spring to autumn depending on which variety you grow. It is evergreen and hardy over much of the UK although I find it to be one of the hardier plants grown.

Ceanothus is a versatile shrub with cultivars that are grow covering, great for covering walls and fences or grown as a small tree. The dark green leaves are one of the darkest colour green foliage you will find growing in the garden.

Ceanothus Varieties

There are a number of Ceanothus varieties in the UK and some of the more commonly available ones are good value shrubs offering year round evergreen foliage and a profusion of blossom in the flowering season.

I have created a list of some of the best Ceanothus to buy in the UK and provided Ceanothus pictures where possible.

As PlantPost specialises in evergreen plants I have not listed any of the deciduous varieties that lose their leaves in the winter. Most of the cultivars listed have an RHS hardiness rating of H4 which makes them hardy to around -10 with the exception of 'Blue Sapphire' and Ceanothus thyrsiflorus 'Victoria' which are rated H5 to -15°C.

I've also listed 'Silver Surprise' which although is evergreen is only rated H3 to -5°C so may suffer damage even in a sheltered location.

Plant Post is a specialist plant site that predominantly focuses on evergreen plants for year round colour and greenery so hardiness has to be taken into account.

Ceanothus arboreus 'Trewithen Blue'

Sporting one of the larger sized leaves for a California lilac at up to 8cm long 'Trewithen Blue' can grow to a small tree. It's also one of the taller growing lilacs with a potential height of 6 to 8 metres although not commonly seen at this size in the UK.

A spring to summer flowering cultivar with sapphire flower buds opening to a gorgeous pale blue colour. I grow this for the foliage which is a glossy mid green unlike the smaller dark green leaved varieties. The pictures show this small tree growing in a north facing location where it only ever gets morning direct sun.

california lilac trewithen blue small tree trewithen blue sapphire buds ceanothus arboreus trewithen blue flowers

Ceanothus 'Autumnal Blue'

Similar in structure and leaf to 'Trewithen Blue' the autumn flowering Ceanothus 'Autumnal Blue' flowers from late summer to autumn.

This variety is unusual not just for its late flowering but for the reddish colour of the stems, particularly the new growth. The leaves are also large as California lilacs go, the dark green contrasting well with the red stems.

It should grow up to 4 metres in height making it a nice small tree. As with all Ceanothus they benefit from growing in a sheltered spot such as next to a wall.

ceanothus autumnal blue red stems ceanothus autumnal blue

Ceanothus griseus var. horizontalis 'Yankee Point'

The ground covering 'Yankee Point' is unusual in that it grows very low to the ground. It can mound up to about a metre in height but in general keeps very low to the ground especially if grown in unfavourable ground and crowded out by other plants.

The pictures are of C. griseus which has been growing in that spot for 5 years and is still doing well. Ceanothus tend not to age well or so I've been told although I have not experienced any losses and my older plants still respond well to pruning after flowering. The images you see are of this low growing California lilac flowering in June.

It is an all round good performing groundcover Ceanothus for the UK remaining evergreen and never having suffered any damage from freezing weather. As a bonus they are very drought tolerant too so do well in long dry summers.

ceanothus groundcover flowers june ceanothus prostrate flowers june

Ceanothus 'Pershore Zanzibar'

One of the hardier variegated Ceanothus cultivars, the exotic sounding Zanzibar sports lime green leaves with dark green splashes. As the leaves age the lime green turns to a pale yellowy cream colour, at least the one I grow do.

Not as vigourous as non-variegated variants but can potentially grow to 2.5m. They seem just as hardy again rated at H4 to -10°C and probably the best of the variegated California lilac cultivars.

The flowers appear in late spring and summer as a mid to light blue but not in as prolific a number as California lilac is famous for. Nonetheless it is grown for the brightly coloured foliage that stands out like a beacon against plainer coloured leaves.

ceanothus pershore zanzibar ceanothus zanzibar foliage

Ceanothus 'Lemon and Lime'

With characteristics very similar to Zanzibar but with narrower foliage 'Lemon and Lime' is one of the newer variegated forms of California lilac. Graham Rice has an excellent write up on the variegated ceanothus he has grown.

This is as hardy as most of the other Ceanothus with variegation and produces a similar blue colour flower over spring to summer. I don't grow this one myself but it purports to eventually grow to about 2.5 metres.

ceanothus lemon and lime

Ceanothus griseus var. horizontalis 'Silver Surprise'

Refined from Ceanothus griseus var. horizontalis 'Yankee Point' by Brand and Sons nursery in England during 1995 and further refined to be released in 2000.

The low growing 'Silver Surprise' should reach no more than a metre and produces green foliage with a creamy off white variegation. Flowers are produced over the spring to summer period and are of a lightish blue hue.

Unusual for Ceanothus this variegated sport is only rated to -5°C which is equivalent to an RHS H3 rating.

ceanothus griseus var horizontalis silver surprise

Ceanothus thyrsiflorus var repens

The Creeping blueblossom is another low growing Ceanothus which stays under 1 metre in height. Typical green foliage about 4cm long and lilac blue flowers in spring to summer time.

You can see the tiny buds in the image as a pale lavender colour. The picture was taken in the UK in April and will soon start to open to show the pale lilac blue flowers. Being drought tolerant and low growing this is a useful plant for pots in a sunny position.

ceanothus thyrsiflorus var repens

Ceanothus 'Blue Mound'

This spring flowerer produces deeper blue flowers in April to May time. It grows to 1.5m so about shrub size ideal for gardens. It has typical evergreen hardiness in the UK taking temperatures down to -10°C and is RHS H4 rated.

The buds start to show in early April with a reddish tinge, as pictured. The coverage of spring flowers is quite dense, typical of California lilac and quite a show.

ceanothus blue mound

Ceanothus thyrsiflorus 'Skylark'

Skylark is one of the larger California lilacs growing to 2.5m and can spread over a similar area. It has smallish mid green leaves and produces summer flowers in large reames in a light blue colour.

Ceanothus thyrsiflorus 'Skylark' is again typical of what you would expect and performs similarly to most other California lilacs. Again a H4 hardiness rating taking temperatures down to -10°C.

ceanothus thyrsiflorus skylark

Ceanothus thyrsiflorus 'Victoria'

Victoria is relatively fast growing with smallish green leaves. I have read reports that this sport could reportedly take temperatures down to -15 although other sources say only -5°C. As this is not one that I grow I cannot comment on its hardiness in the UK.

This is an about average size shrub growing to 1.5 metres high and produces racemes of Late spring flowers.

ceanothus thyrsiflorus victoria

Other Ceanothus Cultivars

Ceanothus 'Blue Jeans' - H4, spring flowering, height to 1.5m
Ceanothus 'Blue Sapphire' (PBR) - H5, hardiest, bronze tint to leaves, flowers spring, height to 1.5m
Ceanothus 'Burkwoodii', H4, late summer to autumn flowers, height to 1.5m, more rounded shiny leaves
Ceanothus 'Cascade' - H4, summer flowers, height to 4m, light blue 8cm long flower panicles
Ceanothus 'Concha' - H4, spring flowers, height to 4m
Ceanothus 'Dark Star' - H4, spring flowers of blue purple colour, height to 2.5m
Ceanothus 'Delight' - H4, spring flowers, height to 3m
Ceanothus dentatus - H4, spring flowers, height to 1.5m
Ceanothus gloriosus 'Emily Brown' - H4, spring flowers, height to 1m
Ceanothus griseus - H4, spring to summer flowers, height to 4m
Ceanothus griseus 'Diamond Heights' - H4, spring flowers, ground cover to 30cm, yellow lime green leaves with dark green centre
Ceanothus impressus 'Puget Blue' - H4, summer flowers, height to 3m, bright blue flowers
Ceanothus 'Italian Skies' - H4, spring flowers, height to 1.5m
Ceanothus 'Puget Blue' - H4, spring to summer flowers, height to 2.5m
Ceanothus 'Snow Showers' - H4, spring to summer white flowers, height to 2.5m
Ceanothus thyrsiflorus 'Mystery Blue' - H4, spring to summer flowers, height to 2.5m

Ceanothus Hardiness

For the evergreen varieties for most parts of the UK they tend to be hardy and not suffer any damage above -5°C. I have grown a variety in different locations including sheltered sunny positions to more exposed north facing locations and never suffered any cold damage. That being said they do benefit from sheltered sunny positions.

frost on Ceanothus yankee point

As far as my research goes the hardiest cultivar is 'Blue Sapphire' being given an RHS hardiness rating of H5 which should mean the plant can take short periods as low as -15°C. If you live in a more northerly or exposed part of the UK then this might be a more suitable choice.

Ceanothus Flowering

California lilacs can produce a prolific amount of flowers over a relatively short period. Flowering tend to last from 2 to 4 weeks with the majority of varieties producing flowers over a 4 week period.

The flowering period for most Ceanothus tends to be from the start of March till June with cultivars such as 'Blue jeans' leading the vanguard where the likes of Skylark will be in flower in June.

The exception to the spring to summer flowering rule for Ceanothus is the sport 'Autumnal Blue' that flowers in Summer to early Autumn and can be seen with flowers in October. It is also one of the faster growing cultivars putting on about half a metre in height a year.

Colour Range Of California Lilac

Evergreen Ceanothus range in colour for both foliage and flowers. The flower colour crosses the blue tones from blues (deep blue, powder blue, violet blue) to lilacs and lavender purple. There is even a white flowering evergreen variety 'Snow Showers' that produces small flurries of pure white flowers.

Leaf colour generally ranges from the mid to dark green and ranges in size from 5 to 10mm up to around 8cm in length. Colour variation comes in the form of the variegated sports that can have leaf colours of a white cream, lime green and pale yellow on a mid to dark green leaf.

Variegation tends to mean more tender although I have found 'Pershore Zanzibar' to be quite reliable. Since I have been growing it the plant has only been exposed to short periods down to -5°C and remained undamaged.