"What the is that??!" is what I thought when I came across this plant in a client's garden last year. It took a while to figure it out, but I eventually concluded that this amazing, improbably hardy perennial is Deinanthe caerulea, a native of the Hubei province in China. Also known as false hydrangea, it is an herbaceous perennial which typically grows to 12-18” tall with a 2' spread. It is currently very hard to find in North America but appears to have a growing fan base in the UK.
It is best grown in peaty, fertile, humus-rich, well-drained but consistently moist soils in light shade. Tolerates full shade but avoid full sun. Performs best in cool summer climates. Intolerant of drought or strong, desiccating winds.
Erect stems rise from woody rhizomes to 18” tall and are topped by large hydrangea-type leaves which are crinkled, rough-textured, with serrated edges and uniquely dual-pointed tips. Nodding, cup-shaped, violet-blue, ( 1 1/4” wide) bloom in clusters above the foliage in June-July. The petals of each flower curl around a decorative central boss of light violet stamens.