I first encountered Clematis 'Dutch Sky' on a trip to The Netherlands while Joe Henderson and I were visiting the plant nursery capital of Boskoop. Somewhere during our travels it was recommended to us to visit the nursery, Marco de Wit Boomkwekerij. I was there to research possible plants to include in our 2014 clematis trial for trial participant gardens Chanticleer, Longwood Gardens and The Scott Arboretum of Swarthmore College in southeastern Pennsylvania, USA. While walking through the flowering potted clematis area of the nursery, I noticed young plants full of the palest blue-to-white blossoms. This turned out to be C. 'Dutch Sky'. We included this cultivar in the trial that year, and after three years of collecting data, C. 'Dutch Sky' was one of the top three plants at all three trial locations, thus earning it the number one/most highly rated plant in the trial. C. 'Dutch Sky' resulted from the breeding program at Marco de Wit Boomkwekerij, and was the work of Marco's cousin, John Kraan. The original goal of the breeding program was to develop a white C. 'Jackmanii'. Though the breeding effort fell short of a true white, they thought this plant was worthy of propagation and it was introduced onto the market in 2008 as C. 'Dutch Sky'. As a young plant, they noted it as a "fresh, healthy, free-flowering plant of which the white flowers with a hint of gray and blue made me think about the sky in Holland," said Marco. For me, the flowers open a very pale blue and the tepals mature to white (or white with the faintest hint of gray) and the tepals are tipped with blue which then matures to a very pale blue. From a distance this coloration reads as bright white with the faintest blush of pale blue. The nursery describes this plant as growing 250 to 300 cm (8 to 10 feet). For me in my home garden and at the Scott Arboretum, it is a vigorous plant easily reaching that height climbing an obelisk. C. 'Dutch Sky' is in the late large-flowered group of clematis [most likely in the "Profuse Clematis" range with the Society's new classification scheme]. Using Pruning Group 3 with late winter pruning to 50 cm (20 inches), flowering time in Holland is July-September. For me, near Philadelphia, USA, flowering is from late May through early July [USDA hardiness zone 7a]. Flower diameter is 8-10 cm (3-4 inches). Flowers have 4 to 6 tepals, and yellow stamens. In addition to the very attractive color of the flowers, this plant is very floriferous with lots of flowers open during the duration of the flowering period. I typically cut my plant back to ⅔ to ½ its total height after flowering (for me, in July), fertilize it and water it weekly, and by September I will have some additional flowering. This second flowering for me never matches the show in June. Our July and August weather can be very hot, humid and frequently with a dry spell that might last for several weeks. Perhaps if I did a better job of watering during these times the September reflowering would rival the earlier one.
One additional positive trait for this plant is that, once the blossoms have faded and gone over, the tepals tend to drop off the plant rather than stay attached and progress to an unattractive brown. My hope is that this plant becomes more popular and is more readily available from nurseries and garden centers in the USA. It really is one of "my top five" clematis and I wouldn't be without it!
C. 'Dutch Sky' with many blooms
C. 'Dutch Sky' (left), C. 'Błękitny Anioł' (right)