Among the hardiest of Clematis, 'Blue Boy' will produces endless waves of nodding, bell-shaped, steel-blue flowers from mid-summer to autumn backed by a green foliage.  A non-vining variety it will grow to around 3m and will need to be planted near a fence, trellis or other structure where it can be trained to grow upwards. Alternatively it can be allowed to trail off a wall or slope to great effect.