Kobus Magnolia Plant Profile

kobus magnolia tree in bloom

pyansetia2008 / Getty Images

The Kobus magnolia (Magnolia kobus) is a lovely deciduous small tree for landscapes. It has large dark-green leaves that are obovate in shape and 3 to 8 inches long. Once well established, the tree produces perfumed white flowers up to 4 inches across in early spring before the leaves appear. The fruit is an aggregate (cluster) of dry fruits called follicles. Each one contains reddish-orange seeds. In autumn, the leaves change to an unremarkable yellow or yellowish-brown color.

This slow-growing tree begins with a pyramidal shape, but over the years it branches out into a rounded shape. Kobus is a trouble-free magnolia that has many landscape applications.

Botanical Name Magnolia kobus
Common Names Kobus magnolia, Kobushi magnolia, northern Japanese magnolia
Plant Type Deciduous flowering tree
Mature Size 25 to 30 tall
Sun Exposure Full sun to part shade
Soil Type Rich, well-drained loam
Soil pH 5.6 to 7.5 
Bloom Time Early spring
Flower Color  White
Hardiness Zones 5 to 8 (USDA)
Native Area Japan

How to Grow Kobus Magnolia

Kobus magnolia likes to be planted in rich soil, but it doesn't do well if the soil is excessively dry or wet. It is best planted in a sheltered location where it is protected from high winds. Avoid southern exposures, which may encourage the flower buds to emerge too early. Be patient, as this tree flowers poorly when it is young; it may take as much as 25 years until it reliably flowers in the spring.

This tree likes to form multiple trunks. If you prefer the look of a more traditional single-trunked tree, choose a central leader when it is young and train it to be the main trunk.

Light

Plant this tree in full sun or part shade.

Soil

Kobus magnolia prefers moist but well-draining soil, and it does best in neutral to slightly acid conditions.

Water

Kobus magnolia does well with average watering patterns—about 1 inch per week, through a combination of irrigation and rainfall.

Temperature and Humidity

This tree does fairly well in all conditions found in its hardiness range, provided it gets proper water and is grown in well-drained soil. It has moderate tolerance for drought. Late cold spells can damage flower buds in spring, but this does not permanently damage the tree.

Fertilizer

Magnolias can benefit from light fertilizing in spring in the early years of growth. A cup of granular balanced fertilizer applied around the base of the plant in the first three years is recommended, but after this, it is best to avoid fertilizers altogether.

Propagating Kobus Magnolia

You can propagate this magnolia species by germinating the seeds or rooting cuttings. If you are using seeds, they will need to go through stratification (a period of cold storage) before planting. Trees grown from seed will also take longer to start blooming.

To propagate from cuttings:

  1. In summer, snip a 4- to 6-inch segment of branch containing some soft, fresh leaves near the tip.

  2. Scrape off a segment of bark from the base of the cutting, about 1/2 x 1/2 inch in size, exposing the green inner layer of bark (cambium).

  3. Treat the base of the cutting and the scraped area with a powdered rooting hormone.

  4. Plant the cutting in a pot containing a mixture of 1 part peat moss and 1 part sand (or a commercial rooting mixture).

  5. Place the pot in a sheltered outdoor location that receives indirect morning light.

  6. Mist the stem and water the pot once a day (twice on warm days) until the cutting has established roots.

  7. Once roots are firmly established (usually this takes nine weeks or more), transplant it into a 1-gallon nursery container filled with standard potting soil.

  8. Continue growing the cutting in a pot for one full growing season. At that point, your young tree can be transplanted into the garden.

    closeup showing reddish-orange seeds of the kobus magnolia
    photograph / Getty Images

Varieties of Kobus Magnolia

There are two natural varieties of Magnolia kobus, according to some botanists: var. kobus and var. borealis. Some also believe the star magnolia (Magnolia stellata) is a variety of this species, making it var. stellata.

An interesting cultivar is 'Wada's Memory'. It is sometimes listed as Magnolia salicifolia 'Wada's Memory' or as a hybrid of the two species (named Magnolia x kewensis). It is columnar to pyramidal in form, with large blossoms and blackish-green leaves.

M. Kobus has also been crossbred with the star magnolia (​Magnolia stellata) and the resulting hybrid is the Loebner magnolia (Magnolia x loebneri).

Comparison With Star Magnolia

 Kobus magnolia is very similar to star magnolia (Magnolia stellata) except it is a larger tree. Star magnolia typically grows to only about 15 to 20 feet.

Pruning

Pruning is not usually with Kobus magnolia, although it may be required to remove branches that droop over walkways or driveways, or to remove damaged or diseased branches. Any pruning should be done in the middle of summer once the blossoms have ended and the leaves have appeared.

Wada's memory magnolia variety
Natalia Timchenko / Getty Images 

Landscape Uses

You can use this as a specimen tree to provide early spring interest because it blooms before many other plants do. This is a good magnolia species for those who live in cooler climates. On large properties, it can be used as a tall informal hedge, and it also makes a good tree for woodland borders.

Common Pests/Diseases

Fortunately, there are few problems associated with the Kobus magnolia. Scales may appear, bringing with them honeydew and the possibility of sooty mold. If they do, treat with horticultural oil.

The most common problem is damage to flower buds due to cold. This is most common when southern exposures cause the flowers to emerge too early.