Magnolia sieboldii K. Koch

Belonging to the tight-knit group of species in Section Oyama, Magnolia sieboldii has much in common with its relatives MM. globosa, sinensis and wilsonii. Usually a large, widely-spreading shrub which needs plenty of room to fulfil its potential, its main ornamental feature is its fragrant white flowers, ‘probably the purest white of all the magnolia flowers’ (Gardiner 2000) with prominent red stamens, emerging after the leaves in late May or June and continuing intermittently through the summer. They are usually held below the horizontal rather than facing the ground, showing off the contrasting stamens to good effect. It fruits freely and attractively in gardens, from a young age (Treseder 1978).

It can be distinguished from its close relatives as follows (Xia, Liu & Nooteboom 2008). M. sieboldii differs from both M. globosa and M. wilsonii in its leaves generally being broadest above the middle (vs. below the middle); in the stipular scar almost half the length of the petiole (vs. almost as long); and in the lack of purple in the branchlets; and from M. globosa in its more widely opening flowers, and its lack of rufous hairs on the leaf undersides. It differs from M. sinensis in having fewer secondary leaf veins (6–8 each side of the midrib vs. 9–13); in the stipular scar being slightly shorter (about ½ vs. ⅔ as long as the petiole); and in the lower leaf surface having brown and white multicellular trichomes, and yellow dots (vs. pale yellow viill).

M. sieboldii became known to Western science through the plants of Korean origin cultivated in Japan. It was not then understood that typical M. sieboldii is not a Japanese native, although the horticulturally inferior subsp. japonica exists as rare natural populations scattered across western Japan. Typical subsp. sieboldii had long been cultivated in Japan, where cut flowers are often used to decorate tea houses, although the Japanese association between drooping flowers and death may have limited its popularity as a garden ornamental (Yinger 1980). It was first described as M. parviflora (Siebold & Zuccarini 1846); Koch’s later M. sieboldii is now used because the epithet M. parviflora Blume had been published earlier for another plant. The date of introduction to Europe is uncertain; it probably reached the Veitch nursery around 1879, and RBG Kew had material from the Yokohama Nursery Company in 1893 (Bean 1981). Whether this early material included subsp. japonica (see below) is not known for certain, but better plants with particularly bright red stamens are linked to a collection made by Ernest Wilson in 1918 in the Kumgang (‘Diamond’) Mountains of what is now North Korea (Wilson 1920; Bean 1981). Wilson enthused over the floral display dominated by M. sieboldii with pink Rhododendron schlippenbachii in these mountains (Wilson 1927), encouraging his American gardening audience with their low winter temperatures, ‘more severe than in Massachusetts’ (Wilson 1920).

It has proved an amenable plant in Western gardens. While a moisture retentive, acidic soil in light shade is ideal, it seems to be more tolerant of lime than was once thought, although thin chalk soils are a step too far (Treseder 1978). Wilson’s expectation of cold hardiness was well founded. It is a ‘very easy’, wind-tolerant garden shrub at 62°N in Norway (Larsen 2009), and grows as far east as the Kórnik and Rogow arboreta, Poland (Anisko & Czekalski 1991). In North America it is suited both to the Pacific Northwest and the Northeast (Cover 2004); drier areas and those with hot summers are less appropriate. It seems to be at the very limit of what it can tolerate in the continental climate of Kansas City, Missouri/Kansas (Branhagen 2006).

Nurseryman Neil Treseder (1978) noted that this species layers more readily than most magnolias.

Magnolia sieboldii hybridizes in gardens with M. obovata to give the lovely M. × wieseneri.