Oyama magnolia (Magnolia sieboldii) is a superb, handsome ornamental shrub that’s frequently grown in gardens and public spaces for its elegant flowers that have an alluring fragrance. The foliage is no less attractive – it gives a spectacular autumn interest when it becomes golden yellow. It’s an easy-care shrub with numerous cultivars available.
I. Appearance and Characteristics
Magnolia sieboldii, or Siebold’s magnolia, also known as Korean mountain magnolia and Oyama magnolia, is a species of Magnolia native to east Asia in China, Japan, and Korea. It is named after the German doctor Philipp Franz von Siebold (1796–1866).
Magnolia sieboldii is a large deciduous shrub or small tree 5–10 m (16–33 ft) tall. The stalks, young leaves, young twigs and young buds are downy. The leaves are elliptical to ovate-oblong, 9–16 cm (rarely 25 cm) long and 4–10 cm (rarely 12 cm) broad, with a 1.5-4.5 cm petiole.
The flowers, unlike the spring flowering magnolias, open primarily in the early summer, but continue intermittently until late summer. They are pendulous, cup-shaped, 7–10 cm diameter, and have 6-12 tepals, the outer three smaller, the rest larger, and pure white; the carpels are greenish and the stamens reddish-purple or greenish-white.
Magnolia sieboldii is grown as an ornamental tree in gardens. It is one of the hardiest magnolias, successful in cultivation as far north as Arboretum Mustila in Finland. The cultivar ‘Colossus’ has gained the Royal Horticultural Society’s Award of Garden Merit.
Called mongnan or mokran (목란/木è˜), Siebold’s magnolia is the national flower of North Korea.
Subspecies
There are three subspecies:
- Magnolia sieboldii subsp. japonica. Japan. Low shrub; flowers with 6 tepals and greenish-white stamens.
- Magnolia sieboldii subsp. sieboldii. Japan, Korea, eastern China. Tree or large shrub; flowers with 9-12 tepals and reddish-purple stamens; leaves smaller, rarely over 16 cm.
- Magnolia sieboldii subsp. sinensis. Southwestern China (Sichuan); flowers as subsp. sieboldii; leaves larger, commonly to 22 cm.
II. How to Grow and Care
Oyama magnolia is known for its elegant blooms and relative ease of care in the right conditions. Key care points include maintaining consistently moist soil without waterlogging and ensuring protection from strong winds, which can damage its large, delicate flowers. Special care should be given to light requirements—oyama magnolia thrives in partial shade, where it can receive dappled sunlight, safeguarding its leaves from scorch.
Sunlight
The positioning of your oyama magnolia is also an important consideration. Despite being able to cope with cooler climates, they will prefer a sunny spot in the garden with some partial shade for protection during the summer months.
Temperature
To avoid damaging early flowering buds, keep oyama magnolia in its preferred moderate to warm temperatures. Most varieties can withstand weather conditions in hardiness zones 4-9. Oyama magnolia should only need watering as younger, newly planted trees, or during periods of drought. You can also help your tree retain moisture with a layer of mulch around its base.
Watering
Originating from the understory of East Asian woodlands, oyama magnolia thrives in moist, well-drained soil, mirroring its natural habitat’s consistent humidity. This species exhibits a preference for evenly moist conditions but can tolerate short dry spells. Care should be taken to maintain a watering schedule of once every three weeks to align with its moderate water needs. As an outdoor plant often favored for its ornamental value, oyama magnolia benefits significantly from mulching which helps retain soil moisture and mimics the leaf litter of its native environment.
Soil
For oyama magnolia, a balanced fertilizer promotes vigor and bloom. Apply a time-release granular formulation (10-10-10) in spring as growth resumes, sparingly – one handful per mature shrub. During active growth, liquid feeds can boost health; monthly is ideal, halving in fall. Avoid late season fertilization, which can spur tender growth susceptible to frost. Over-fertilization risks root burn, so follow product guidance. Mulch annually with compost to enrich soil gradually, offsetting heavy feeding needs.
Fertilizing
Planting Instructions
The best time to plant young oyama magnolia is during the spring. Plants should be kept well-watered, and benefit from the addition of organic matter or pre-mixed fertilizer to promote strong, healthy growth. This should be mixed in with the soil around the roots of new plants. Be sure to choose a location with plenty of room for your plant to grow.
Pruning
Oyama magnolia requires little pruning. In fact, pruning can harm the trees or prevent flowering if pruned back too hard. Therefore, a light trim of younger trees during late spring/summer after they have finished blooming is all that is recommended to help shape your plant and to encourage more blooms in the coming years. Remove any damaged branches and ones that are crossing over. You can also trim back any extra-long, leggy shoots. Consider the tree shape when pruning your oyama magnolia, and always aim for a balanced, open structure.
Propagation
Oyama magnolia is a deciduous shrub known for its attractive, fragrant flowers. For propagation, semi-hardwood cuttings taken in summer give the best results. Ensure cuttings have a few leaves and are about 4-6 inches long. Dip the cut end in rooting hormone and plant in a well-draining soil mix, keeping it moist until roots develop. With patience and care, gardeners can successfully cultivate new specimens to enhance their outdoor spaces.
Transplanting
The best time to transplant oyama magnolia is during the gentle warmth of late spring to early summer, ensuring a harmonious balance for root establishment. Choose a shaded location with well-drained soil. If possible, maintain soil consistency to ease transition for oyama magnolia.
III. Uses and Benefits
Oyama magnolia is a beautiful addition to city gardens, cottage gardens, woodland gardens, patio containers, and small gardens.
