This grower is sure of this plant identification.
Astilbe × arendsii. This is a leafy perennial that is grown for its tapering plumes of tiny flowers which come in a large variety of colours. The flowers will dry on the plant and remain as an ornamental footnote for the autumn and winter garden.
They are fully hardy and will need rich moist soil and some will need partial shade. Leave undisturbed if possible, and give an annual spring mulch of well rotted compost.
Border, dried arrangements, cutting bed, rock garden