Color: Blue Flower Size: 6-8″ (15-20cm) Flowering Period: May June & Aug Mature Height: 6-9′(2-3m) Pruning Group: B1 Planting Aspect: Sun/ Partial Shade USDA Zone: 4 Foliage: Deciduous Suitable For Container: Yes Price Group: Standard About Vyvyan Pennell The best known of all the doubles. 6-8″ (15-20cm) double flowers in a violet blue with reddish overtones in May and June, followed by single flowers in a luminous light violet in mid August. Mature height 6-9′ (2-3m). Pruning group B1.