Clematis of the Month for April 2005
How do plant breeders see? Clearly they are endowed with a prescience that we mere gardeners can only guess at. Some are technicians, some are gamblers, and some are visionaries, such as the late Kazushige Ozawa. He imagined a superlative bell-shaped flower of nuanced color appropriate to his audience, performers of the Japanese tea ceremony. This ceremony requires a single evocative bloom to enhance the mood of the ceremony. For this purpose he wed Clematis integrifolia to Clematis reticulata to create C. ‘Rooguchi.’
Clematis integrifolia is, of course, a known quantity, one with a variable and successful history as a parent. The four-sepalled flower can be chaotic, with arms thrown open, or coifed into ringlets, or with sepals folded vertically and rolled back down the middle. C. integrifolia‘s children do not climb, even those co-parented by that estimable climber, Clematis viticella. Mr. Ozawa had raised countless integrifolia crosses, naming only those that met his aesthetic standards, but finding sufficient merit in selected seedlings to use them as anonymous pollen donors to preserve subtle characteristics.
By contrast, Clematis reticulata is a stalwart if unassuming creature. It is an enthusiastic vine, grasping skyward in the classic clematis manner (to 3 metres / 10 feet high). The flower color is a bland green-yellow, sometimes glazed with pink or purple, with this diaphanous color gathering intensity near the peduncles, similar to Clematis versicolor, a near cousin. Brewster Rogerson describes C. reticulata as “putty-colored,” faint praise indeed, but true enough. The sepal reverses are slightly ridged, and not shiny; the whole flower is 2.5 cm (1 inch) long on average. What makes this species worthy of being a parent? The shape of the bell is not the usual viornae urn, with sepals pinching in before flaring out at the tips. The profile of C. reticulata flowers is ramrod straight until the modest spreading of the sepal points. It is this elegance of form that captured Mr. Ozawa’s attention.
C. ‘Rooguchi’ mimics the flower of its reticulata parent on a larger scale, with bells to 5 cm (2 inches) long (especially on the earliest flowers), and strong ridging on thick sepals, somehow deepening the color and intensifying the luster of the integrifolia parent. Pale borders accentuate the four sepals, which are the blue of Italian plums. Whether a given plant of C. ‘Rooguchi’ is young and yielding its first flowers or mature and producing hundreds, all are down-facing and straight-sided with a refined recurve at their tips. This uniformity of flower gives the plant its presence.
The poise and color of C. ‘Rooguchi’, combined with the longer bells made it ideal for Mr. Ozawa’s cut flower trade. It was not until the plant was introduced into international commerce that its virtues as a garden plant were discovered. Because, surprisingly, it can climb (2.5 metres / 8 feet).
As if this were not enough, gardeners in diverse regions discovered that C. ‘Rooguchi’ has also inherited the extraordinary hardiness of its integrifolia parent. Clematis reticulata contributes the ability to withstand high heat and humidity. The lobed foliage is smooth to the touch and a complimentary mid-green. It does not burn in full sun. C. ‘Roguchi’ can spill over a wall, enliven a spring-flowering shrub with its summer bloom, or partner with its fellow clematis, such as C. ‘Huldine’.
The bad news is that young plants and stressed plants of C. ‘Roguchi’ have a tendency to develop powdery mildew. The best way to manage this problem is to hard prune afflicted plants to the ground, forcing clean new growth and ample rebloom. Mature plants, and plants in partial shade that are adequately and regularly watered, rarely attract mildew.
Clematis ‘Rooguchi’ is a plant of instant and enduring popularity, and some might suggest it is the most impressive of the many fine clematis in the legacy of Mr. Ozawa. From the raw materials of Clematis integrifolia and the relatively obscure North American species Clematis reticulata, Mr. Ozawa was able to craft a ground-breaking hybrid.
Linda Beutler and Maurice Horn 