Caryopteris × clandonensis is a compact deciduous shrub in the mint family (Lamiaceae), bred from the Asian species C. incana and C. mongholica. It produces dense clusters of blue to violet flowers from mid-summer through early fall — a window when most other shrubs have finished — and seven of its cultivars hold the RHS Award of Garden Merit.
Grows 2–4 ft tall and wide, performing best in full sun and sharply drained soil. Tolerates drought, lean soil, and alkaline pH once established; heavy clay or persistently wet ground shortens its lifespan. Cut all stems back hard to 6–8 in every spring, since flowers form only on current-season wood. In zones 5–6, top growth may die back in hard winters but the plant typically regenerates from the crown. A light mulch around — not against — the base helps moderate soil temperature.
The late-season flowers are a concentrated nectar source for bees, butterflies, and other pollinators at a time when many foraging plants have declined. In mixed borders it bridges the gap between peak summer color and fall-blooming perennials.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.
Verticillium Wilt
Lower leaves yellow and wilt, often on one side of the plant, with brown streaking in the stem and crown tissue when cut open. Plants are stunted and decline over the season.
Remove and destroy affected plants. Avoid planting in soil that has grown infected tomatoes, peppers, or other susceptible crops. Rotate beds and improve drainage; there is no cure once a plant is infected.