Tree of Merit: Kobushi Magnolia
(Magnolia kobus)
by Ian "Mac" McDermott , Educator & Course Manager in Arboriculture,
Pershore College, Worcestershire, U.K
The Kobushi or Kobus magnolia is closely related
to Magnolia stellata, a commonly planted species
in gardens. My attention was first drawn to the
Kobushi magnolia by the Municipal Arboriculturalist
for the London Borough of Barnet after he read
research in the Journal of Environmental Protection
and research in Plant, Cell & Environment citing
this tree as being among the best for the removal
of nitrogen dioxide (NO
2
) from the atmosphere.
Given that air quality (AQ) is an international issue
of great concern, and that Barnet is a north London
Borough with all the AQ issues of any inner-city area,
the need to consider such tree qualities was clear—
and the tree was planted widely in Barnet. It has done
extremely well as a street tree, and a number of other
authorities are now following suit with street tree
plantings as well as the more usual park specimens.
Kobushi magnolia originates from Japan and South
Korea where it grows on calcareous soils, which
bodes well for its use in concrete-heavy environ-
ments. It is hardy to RHS Zone H6-H7 and USDA
Hardiness Zone 5a. Kobushi can tolerate moderate
shade and waterlogged soils but is somewhat sensi-
tive to drought. In urban settings it can reach about
9 metres (30 feet) tall by 11 metres (35 feet) wide.
The fragrant, showy white flowers on naked branches
in the spring make a big visual impact. Like most mag-
nolias, the tree bark is smooth. Here in the United
Kingdom, Kobushi tends to be trained to grow as a
single-stem tree. The seeds are favoured by birds.
So far there have been no reports of any serious
infrastructure implications; it would be fair to con-
sider that the mature size would probably preclude
it from any serious damage to footways and car-
riageways. In its compact size, Kobushi seems to be
suitable for smaller planting strips in narrower roads.
Pruning should ideally be undertaken in late summer;
usually this is confined to structural and sanitation
pruning, as the compact form should not require undue
attention from the pruning saw. Kobushi is noted to have
some occasional infestation with horse chestnut scale
(Pulvinaria regalis) but this seems to be limited and not
fatal. However, the tree is not resistant to honey fungus
(Armillaria sp.), so caution is required on infected sites.
Kobushi is readily available in a range of sizes from
tree nurseries here in the United Kingdom. A tes-
tament to their current favour is they are quite
hard to purchase, as they sell out a season in
advance as authorities attempt to battle the issues
of poor air quality in a sustainable way.
Images below courtesy MOBOT Plant Finder
Kobushi trunk. Kobushi magnolia flower. Kobushi foliage and
developing seedpod.
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