Photo: unknown author, USFWS, Public domain · source
Pruning guide · Shrub
Californian lilac: when and how to prune
Ceanothus
Prune an evergreen Californian lilac straight after flowering, in June–July, and only this year’s growth; prune a deciduous one in March–April, back to 2–3 buds.
Ceanothus comes from California and is one of the few shrubs with truly blue flowers. There are two groups, and you prune them very differently. The evergreen species flower in May–June on last year’s wood and don’t tolerate hard pruning: bare old wood won’t sprout again. The deciduous species flower from July to October on new wood and can be cut back hard every spring. So first check which one you have.
| Pruning months | March–April and June–July |
|---|---|
| Nesting season (15 March–15 August) | Take care in March–April and June–July |
| Flowering | May–July |
| Native to Belgium | No, planted |
Californian lilac: when to prune it?
Prune an evergreen ceanothus straight after flowering, in June–July. It then still has the whole summer to make new shoots that will flower next year.
Prune a deciduous ceanothus in March–April, before it comes into leaf. It flowers later in summer on the new shoots.
Cut out frosted branches in spring, as soon as you can see what is sprouting again. Never prune in autumn: the wounds and young shoots make it more vulnerable to frost.
What else to prune in those months? March · April · June · July
Californian lilac: how to prune it?
- Evergreen species: only shorten this year’s growth, to just above a leaf or a side branch. Never cut into the old, bare wood.
- Deciduous species: cut last year’s shoots back to 2–3 buds above the older wood. That gives vigorous shoots with large flower clusters.
- Against a wall: tie the branches in as a fan, and after flowering shorten the shoots growing away from the wall.
- Cut frosted branches back to healthy wood. If an evergreen shrub is badly frosted, wait until June: sometimes it still sprouts.
- Don’t try to rejuvenate an old evergreen ceanothus that is bare at the bottom: replace it with a young plant. So take a few cuttings in summer as a reserve.
How much to cut, and how often?
- Evergreen: little, only this year’s growth, a bit every year.
- Deciduous: every spring, all of last year’s shoots, back to 2–3 buds.
What does it mean for wildlife?
- Pruning in June–July falls in the nesting season (15 March–15 August). Blackbirds and dunnocks like to nest in a dense ceanothus against a wall: look carefully first, and spare an active nest.
- The blue flowers attract honeybees, bumblebees and wild bees from far away. The evergreen species flower in May–June, the deciduous ones fill late summer.
- When you prune the evergreen species after flowering, you also cut off the seed capsules; by then the flowering for the bees is already over.
- Plant it with other flowering plants for dry, sunny spots, such as lavender, rosemary and thyme: that way your garden has flowers for bees from spring to autumn.
Common mistakes
- Cutting an evergreen ceanothus back hard, so it doesn’t sprout again.
- Pruning a deciduous ceanothus in summer, so the flowers are lost.
- Throwing away a frosted shrub too soon, before it had a chance to sprout.
- Pruning in autumn, so the shrub becomes more vulnerable to frost.
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.
Nearby: related pruning guides
Similar to: Difference from common lilac · Difference from butterfly bush
Plant profile: Californian lilac · Pruning calendar and basic rules