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All ratings refer to the UK growing conditions unless otherwise stated. Minimum
temperature ranges (in degrees C) are shown in brackets
AGM plants have been through a rigorous trial and assessment programme. They are:
This plant will provide nectar and pollen for bees and the many other types of pollinating insects.
It is included in an evolving list of plants carefully researched and chosen by RHS experts. Divided into 3 groups these lists, linked below, are maintained by a team of RHS staff and are reviewed annually.
'Giotto' is an erect herbaceous perennial to 1.5m in height, with divided foliage and erect spikes of deep blue and violet, semi-double flowers 7cm across, with pale brown eyes
'Celebration' is an erect perennial with spikes to 65cm long, and numerous side branches, bearing semi-double pale cream flowers 7cm across, with grey-brown eyes
'Clifford Sky' is a tall perennial with white-eyed, semi-double sky-blue flowers 7cm across, in branched spikes in summer
'Margaret' is an erect, vigorous perennial, branching and floriferous. Flowers are bright mid-blue, with large white eyes which may show a blue splash
'Guardian Blue' is an upright herbaceous perennial 1.2m high with divided green leaves and strong stems, especially suitable for cutting, of deep blue flowers with white centres in early summer; delphiniums may be visited by bumblebees, especially long-tongued bumblebees
'Pink Sensation' is a short-lived perennial with deeply divided leaves and slender spikes of small dusky pink flowers in summer and autumn
'Franjo Sahin' is a tall, upright perennial to 2m with a mound of glossy, divided foliage and tall spires of semi-double flowers in early to mid-summer. The petals are pale purple with a dark purple edge, and the eyes dark brown
'Langdon's Blue Lagoon' is an erect, vigorous perennial to 195cm, branching and floriferous, with large green leaves. Spikes to 90cm long, flowers 7cm across, mid-blue with white eyes
'Loch Leven' is an upright perennial to 1.5m in height, with white-eyed, light blue flowers in erect racemes to 90cm in length
'Summer Nights' is a low-growing, short-lived perennial growing to 30cm tall and wide. In summer, loose sprays of single, spurred, bright blue flowers are held above the low, bushy mounds of foliage
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