Californian lilac

Californian lilac: how do you recognise it?

Habit

Shrub of 1–3 m, upright or spreading; some forms stay low and creeping.

Leaf

Alternate, 1–7 cm, oval to elliptic, finely toothed and glossy; often with three distinct veins from the base or with deeply impressed veins.

Bark

Green to reddish-brown twigs.

Flower

Dense clusters of small blue, sometimes white or pink flowers; the evergreen species flower in May–June, the deciduous ones from July to October.

Fruit

Small, three-angled capsules.

Difference from lilac

Lilac has large, heart-shaped leaves and big lilac flower clusters on a tall shrub.

Difference from butterfly bush

Butterfly bush has long, narrow, grey-felted leaves and long purple flower spikes.

Flowering: May–July · Pruning: March–April and June–July

Identify by feature: Purple or blue flowers

Looks like it, but isn’t

• Common lilac Syringa vulgaris: large, heart-shaped leaves and big lilac flower clusters on a tall shrub. Difference from common lilac
• Butterfly bush Buddleja davidii: long, narrow, grey-felted leaves and long purple flower spikes. Difference from butterfly bush

Why grow it?

• Truly blue flowers, a rare colour among shrubs.
• A magnet for bees in May–June or, with the deciduous species, in late summer.
• Fixes nitrogen from the air: grows on poor, dry soil without fertiliser.
• Ideal against a warm wall or in a sunny, dry spot.

Californian lilac: where does it grow best?

• Full sun, sheltered from cold wind; against a south- or west-facing wall it flowers best and comes through winter most safely.
• Dry, well-drained soil; poor soil is no problem, wet feet in winter are.
• Allow 2 m width; against a wall it can be trained flatter.

Light

Full sun

Legal basis

Any garden soil

Moisture

Dry

Size

2 m tall, 2 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Broom: Yellow flowers in May next to the blue: two nitrogen fixers for the same poor, dry soil.
• English lavender: Another sun-lover for dry soil, which carries on flowering for the bees after the evergreen ceanothus.
• Rosemary: Evergreen and fragrant, for the same warm, dry spot against a wall.

Good and bad companions

Best kept away from

• Do not plant under the dense crown of these trees: norway spruce, european silver fir, nordmann fir, douglas fir, yew, horse chestnut, norway maple, sycamore

Californian lilac: when and how to plant it?

1. Plant from a pot in spring (April–May), so it is well rooted before winter.
2. Choose a young plant: older shrubs resent being moved.
3. Plant at the same depth as in the pot and, on heavy soil, mix coarse sand or gravel into the planting area.
4. Against a wall: plant it 30–40 cm from the wall and tie the branches to wires.

Care

Watering

In dry spells in the first year; hardly at all after that: it likes dry conditions.

Feeding

Not needed: it fixes its own nitrogen. Fertiliser gives soft, frost-tender growth.

Tying in

Tie the branches of a wall-trained plant to the wires regularly.

Successor

Evergreen species rarely live very long: take cuttings for a replacement in good time.

Tip: If you live inland or in a cold spot, choose a deciduous variety such as ‘Gloire de Versailles’: it flowers on new wood, so even after a severe winter. An evergreen ceanothus is best planted against a south-facing wall.

Californian lilac: when to prune it?

Pruning months: March–April and June–July.

When: Evergreen species straight after flowering (June–July); deciduous species in March–April.

How:

• Evergreen species: only trim the current year’s growth, never into old wood, as they will not sprout from it.
• Deciduous species flower on new wood: in March–April, cut last year’s shoots back to 2–3 buds.
• In spring, cut frost-damaged branches back to healthy wood as soon as you can see what is sprouting.

Caution: Never cut an evergreen ceanothus back hard: bare old wood will not sprout again. June–July falls in the nesting season: check for nests first.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

In summer, take 8–10 cm semi-ripe cuttings and root them in sandy compost under glass or plastic. That way you have a successor ready.

Californian lilac: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Evergreen species survive an ordinary winter in a sheltered spot, but hard or prolonged frost, around −10 °C and below, can badly damage or kill them, especially with cold wind or on wet soil.
• Deciduous species are tougher. If they are killed back, they usually resprout in spring and flower as normal on the new wood.
• Protect young plants with horticultural fleece in hard frost; they are safest against a warm wall.

Diseases and pests

• Frost damage: Brown leaves and dead branches after a severe winter. Wait until spring, then cut out the dead parts.
• Sudden death: On wet, heavy soil the roots rot, and older evergreen shrubs sometimes die quite suddenly. Plant on well-drained soil and keep a cutting in reserve.
• Bare base: An old evergreen shrub becomes bare at the base and will not resprout after hard pruning. Replace it with a young plant.
• Scale insects: Brown, domed scales on the twigs and sticky leaves. Rub them off or cut out badly affected twigs.

Through the year

• March: Prune deciduous species back to 2–3 buds.
• April: Last pruning month for deciduous species; cut out frost damage; plant.
• May: Evergreen species in flower: blue and full of bees.
• June: Lightly prune evergreen species after flowering; check for nests first.
• July: Last pruning month for evergreen species; the deciduous ones start flowering.
• August: Take cuttings; deciduous species in flower.
• December: Protect young plants in hard frost.

What can you use it for?

Garden and landscape

One of the few shrubs with truly blue flowers; for a sunny, sheltered spot or against a warm wall.

For wildlife

A magnet for bees; fixes nitrogen from the air.

Caution: The evergreen species are not fully hardy and rarely live very long.

Did you know?

• Like alder and sea buckthorn, ceanothus fixes nitrogen from the air, with the help of bacteria in nodules on its roots.
• Its English name is Californian lilac, but it is not related to lilac: it belongs to the buckthorn family.
• In California it grows in chaparral, a dry scrub that burns regularly: its seeds germinate particularly well after the heat of a fire.