For carefree color in a shady garden, consider astilbe, which produces feathery plumes of white, pink or red flowers from late spring through summer. The rest of the year, the attractive divided leaves effectively block light from reaching the soil, which helps to keep weed seeds from sprouting. 'Ostrich Plume' (also known as 'Straussenfeder') has arching sprays of pink flowers, while Astilbe x arendsii 'Fanal' has erect spikes of bright red flowers.
Most varieties grow 2-3 feet wide and around 3 feet tall. Does best in part shade, though full sun is OK in cool areas, with regular water. Perennial in zones 4-9