Clematis 'Zoblueriver' BLUE RIVER

Clematis of the Month for March 2022

described by Brigitte Niemela

C. 'Zoblueriver' BLUE RIVER©Brigitte Niemela

C. 'Zoblueriver' BLUE RIVER

Clematis 'Zoblueriver' BLUE RIVER is a variety from the Dutch breeder Wim Snoeijer, who works for the J. van Zoest clematis nursery. Launch was in 2008.

On the company's website there is a list of the ten best and easiest-to-grow varieties by color. Clematis BLUE RIVER is mentioned in this list under the group of pale violet-blue clematis. And rightly so. Because it really is an easy-care plant: robust, reliable and very hardy. The very lush flowers in a refreshing shade of blue should also be emphasized.

Botanical classification

The breeder, Wim Snoeijer, is much engaged with the classification of clematis and has written a book about it. The book is presented on the International Clematis Society's website, see I'm very happy to own a copy of this book. It's not a book to be read in one go. But every time I pick up the book, I discover information that I haven't read anywhere else before. Wim works a lot with diagrams to show the relationships between the clematis groups. My botanical knowledge is far too limited to see through all the intricacies of classification. But reading the book has definitely sharpened my view of the characteristics by which clematis can be distinguished and assigned.

The Royal Horticultural Society RHS is the International Cultivar Registration Authority for the genus Clematis. In this Register BLUE RIVER is listed under Clematis integrifolia.

[Editor's Note: To clarify this, in "The International Clematis Register and Checklist, Third Supplement", no group is given for C. 'Zoblueriver'. Instead, at the end of the entry it states "The registrant assigns to Diversifolia Group". On the RHS website, however, it is shown as in the Integrifolia Group. As editor, I always use the definition in the Register.]

There is no Diversifolia Group in the RHS Clematis Register. Going through the websites of different nurseries you will find, that some of them also list C. 'Zoblueriver' BLUE RIVER in the Integrifolia Group. In contrast, Wim Snoeijer assigns the variety to the Diversifolia Group. According to his opinion the variety should rather be listed in the Patens Group than in the Integrifolia Group when the Diversifolia Group is not acknowledged.

In his above mentioned book Wim explains, why a separate group for Clematis diversifolia is justified.

Growth habit and flowering

C. 'Zoblueriver' BLUE RIVER is a non–clinging, herbaceous clematis. Without support, it scrambles mat–like along the ground. The shoots reach a length of 140 to 180 cm (4½ to 6 ft). This is relatively long for a herbaceous clematis. If it is to grow up to a support, it must be tied up.

C. 'Zoblueriver' BLUE RIVER showing development of buds©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER showing development of buds

C. 'Zoblueriver' BLUE RIVER with twisted sepals©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER with twisted sepals

C. 'Zoblueriver' BLUE RIVER with Rosa HARLOW CARR and Rosa ARTEMIS©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER with Rosa HARLOW CARR and Rosa ARTEMIS

The main flowering period extends from June to August. Flowers continue to form until September. The buds stand upright at first and then slope sideways. In this lateral position, the flowers open in a funnel shape. They expand to a star shape until they are almost completely flat. The color changes from lavender purple to a radiant sky blue. The furrowed central stripe is tinged with rosé. Long, white stamens match perfectly. They remind me of fluffy white clouds in the summer sky. The anthers soon turn beige-brown. Slightly twisting sepals make the flower look lively. With a diameter of six to eight centimeters, the flowers are relatively large for a herbaceous clematis. It is also an excellent cut flower.

C. 'Zoblueriver' BLUE RIVER is an excellent cut flower©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER is an excellent cut flower

C. 'Zoblueriver' BLUE RIVER and Rosa ARTEMIS©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER and Rosa ARTEMIS

C. 'Zoblueriver' BLUE RIVER beneath the well known C. 'Jackmanii'©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER beneath the well known C. 'Jackmanii'

C. 'Zoblueriver' BLUE RIVER in a mixed border©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER in a mixed border

C. 'Zoblueriver' BLUE RIVER two weeks later in the same mixed border©Brigitte Niemela
C. 'Zoblueriver' BLUE RIVER beneath the well known C. 'Jackmanii' two weeks later in the same mixed border

Planting and care

C. 'Zoblueriver' BLUE RIVER should be planted a few centimeters lower than it was in the pot. It has fleshy roots from which more and more down-to-earth shoots sprout over the years. This allows to propagate the plant by division of the rootstock after a few years. The soil should be rich in nutrients and moisture but well-drained. A sunny to partially shaded location is ideal.

In spring give it a hard pruning to a hand’s breadth above the ground. A first dose of fertilizer in March and top-up fertilizing in June ensure lush flowering. It is also grateful for a good water supply during longer dry periods. When the clematis is to grow up a vertical climbing frame, regular tying is very important. Otherwise there is a risk that the shoots will tip over and break. C. 'Zoblueriver' BLUE RIVER is also well suited for planting in a container.

Brigitte Niemela Brigitte Niemela

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