Ceanothus shrubs are evergreen or deciduous, so prune according to what type you have.
Routine pruning is not essential and in fact are best not pruned. If grown as a bush, promote branching by pinch-pruning the soft tips on young plants in spring. Use secateurs to shorten over-long branches by up to a half in midsummer after flowering. Do not cut into older wood as the stumps may not regrow.
Late summer-flowering shrubs: These bear spring flowers on shoots that grew the previous summer and summer flowers on the current year's growth. Trim the previous season’s growth by one-third to a half in spring. (e.g. C. ‘Autumnal Blue’, C. ‘Burkwoodii’)
Late-spring and early-summer flowering shrubs: Prune after flowering. Cut back long, flowered shoots by one-third to a half. If more bushy growth is desired, trim lightly again in late summer. (e.g. C. arboreus ‘Trewithen Blue’, C. dentatus, C. impressus, C. thyrsiflorus ‘Skylark’)
To grow as a wall shrub see our advice in climbers and wall shrubs.
Prune deciduous Ceanothus (e.g. C. × delileanus ‘Henri Desfossé’ and ‘Gloire de Versailles’, C. × pallidus ‘Perle Rose’) in early to mid-spring. These bear summer flowers on new shoots each year and routine pruning is usually carried out to generate many strong new shoots each year.
First and second years: To develop the main framework of branches of free standing shrubs, shorten all stems by up to two-thirds, cutting back to an outward-facing bud. In the second year, prune the previous season’s growth by up to two-thirds and shorten all side branches to 10-25cm (4-10in) from the main stems.
On established plants: Prune main, flowered stems by about a half. Cut back weaker sideshoots harder – by up to about two buds. Thin out congested or unproductive growth from the centre of the shrub. The response of deciduous Ceanothus to hard pruning is usually good.
Renovating overgrown plants
Overgrown evergreen Ceanothus will not respond well to renovation pruning. In this case you'd be best off replacing the plant.