The Japanese Hostas, Part 11 Hosta sieboldii (Koba Giboshi)

Though hostas are native to Japan, China, and Korea, the majority of species come from Japan. This article is the eleventh in a series which will talk about those species. Previous eNewsletter articles have covered Hosta alismifolia, H. nakaiana, H. pycnophylla, H. longipes, H. longissima, H. montana, H. kikutii, H. tibae, H. rupifraga, and H. takahashii. If you missed any of the past articles, you can find them on my blog site: https://thecottagegardener53012.wordpress.com.

Today we will discuss H. sieboldii, Koba Giboshi, which is one of only two hostas native to the entire Japanese archipelago (H. montana is the other). A very adaptable plant, it grows in woodlands, swamps, and grasslands. The form found in the wild is identified as H. sieboldii var. sieboldii and forms a small clump, about 14 inches tall. The medium green leaves are shiny on both the top and bottom and are of thin substance. Because of the wide native range, the species is very diverse, differing in mound size, leaf size and shape, waviness, and coloration. Various subspecies and forms reflect these deviations. For example, H. sieboldii f. angustifolia has a more elongated leaf that has a wavy margin. In addition, H. sieboldii readily mutates.

Flowering generally occurs in August. Though most are of a medium purple color, it can range from deep purple to white. Typically the flower petal margins are white, as is mid-petal striping. A naturally occurring all white flowered form is known as H. sieboldii f. alba. Flowers of H. sieboldii are both male and female fertile and naturalize readily. Scapes are 22 to 31 inches long.

For many years, H. sieboldii ‘Albomarginata,’ a white margined form, was considered the type-form of the species. It was discovered in Japan in the early 1800s and was likely one of the first live specimens of hostas brought from Japan into Europe, having been brought to the Netherlands by Philipp von Siebold in about 1830. Though it was found in the wild, it is not self-perpetuating; the white margin is not inherited through normal seed propagation. Seedlings of ‘Albomarginata’ will likely be all green and should be referred to as H. sieboldii var. sieboldii, formerly H. sieboldii f. spathulata.

            Hosta sieboldii is often confused with H. ‘Lancifolia’ because of the similarity in plant size and leaf shape. However, enough differences exist to make them distinct. In the flowers, H. sieboldii has yellowish-white anthers while those of ‘Lancifolia’ are purple. ‘Lancifolia’ blooms later than sieboldii and is sterile. H. sieboldii is fertile. The flower scape of ‘Lancifolia’ usually has sterile bracts attached to it; they are absent in H. sieboldii. Leaves of ‘Lancifolia’ have a greenish-purple petiole with spots near the base. The petiole of H. sieboldii is green and spots are absent. In addition, the leaves of ‘Lancifolia’ are shinier than those of H. sieboldii.

Many seedlings and mutations of H. sieboldii are important in the hosta industry. ‘Beatrice,’ ‘Neat Splash,’ and ‘Yellow Splash’ are streaked mutations that have been used to breed variegated plants. Alone they are unstable, but have resulted in many sports and hybrids. MyHostas database lists 48 plants that came from ‘Beatrice,’ 70 from ‘Neat Splash,’ and 25 from ‘Yellow Splash.’

A few of the notable H. sieboldii sports include ‘Kabitan,’ which is chartreuse with a dark green edge, ‘Carrie Ann,’ a white margined sport, and ‘Painted Lady,’ a sport of ‘Albomarginata’ that is green and white streaked with a white margin. ‘Butter Rim’ is a yellow edged seedling, ‘Emerald Isle’ a seedling with a white edge and white flowers, and ‘Masquerade,’ formerly identified as H. venusta ‘Variegated’ is a seedling which is white with a green edge. It tends to readily revert to all green.

One of the notable hybrids is ‘Honeybells,’ a cross between H. plantaginea and H. sieboldii that is known for its fragrant flowers. Also of this parentage is ‘Emily Dickinson.’ One of my favorite dark green hostas, ‘Midnight Oil,’ is the result of a cross between ‘Potomac Pride’ and ‘Neat Splash Rim,’ the stable form of ‘Neat Splash’ which has a green center and creamy white margin.

Hosta sieboldii has been and still is an important hosta species. As noted, it has been extensively used by hybridizers, but is an outstanding plant in its own right. It makes an excellent massing and naturalizing plant and can be used as a ground cover or to edge a bed or path. No garden should be without it.