Deutzia gracilis

Deutzia gracilis, the slender deutzia, is a species of flowering plant in the hydrangea family Hydrangeaceae, native to Japan. It is a deciduous shrub with opposite, simple leaves, and slender, arching stems. The flowers are white, borne in spring and summer. 
The compact cultivar 'Nikko', growing to tall by broad, has gained the Royal Horticultural Society's Award of Garden Merit. 