FORESTRYJOURNAL.CO.UK AUGUST 20 19 93shores was very limited, until 1854. By the
1870s, Japanese gardens, complete with
Japanese maples, were established across
the British Isles. A. palmatum continues to
be a prominent subject in Japanese art and
design. The numerous cultivars now exceed
1,000 in number, with red-leaf varieties most
favoured in Europe and North America,
closely followed by the cascading green-
leaved cultivars.
GROWING CONDITIONS
A. palmatum now exists in
a huge variety of forms.
As such, it is difficult
to generalise about
growing requirements,
but core conditions are
similar to the needs of
wild trees.
A. palmatum is a
generally slow-growing
species, with some cultivars
tolerating full sun, although the
vast majority prefer partial shade,
especially when grown in warmer and
sunnier climates. As a general rule, green
and pale-leaved cultivars prefer dappled
but not dense shade, while purple-leaved
cultivars need a sunnier spot to maintain
their inherent hues during the growing
season. Trees are highly adaptable in relation
to companion plants, despite Japanese maple
typically being grown in its own space.
Trees are especially suitable for borders
and ornamental pathways, because the
roots are compact and non-invasive. Smaller
cultivars can be successfully grown in
containers. Trees do best in moist but
well-drained, slightly acid soils and, while
susceptible to drought, will not tolerate
waterlogged soils.
Seeds need a period of stratification
for germination. The many hundreds of
cultivars selected for specific
characteristics are commonly
propagated by grafting, but
also by cuttings, layering
and tissue culture.
Newly planted trees
should be mulched
with a thick layer of
bark and receive only
a light application of
slow-release fertilizer
comprising a 3:1 ratio of
nitrogen to phosphorous. A.
palmatum trees do not respond
well to heavy dressings of fertilizer.
Nitrogen-based lawn fertilizer should not
be applied in the vicinity of trees planted
in turf. Excess nitrogen promotes highly
vigorous growth more susceptible to disease.ALIEN BEETLE PEST
A. palmatum is a popular line in garden
centres, including expensive cultivars grown
in containers for many years, regularlycosting £100 or more. Supermarkets, on the
other hand, tend to ‘stack ’em high and sell
’em cheap’ at a few pounds a pop.
Perhaps Japanese maple should be
renamed ‘Chinese maple’, because most
plants on sale originate in China, having
arrived in the UK via the Netherlands.
However, also originating in China is
the citrus longhorn beetle (Anoplophora
chinensis), a serious invasive insect pest,
the larvae of which feed undetected inside
trees to make them more susceptible to other
insect pests and diseases.
In February 2010, citrus longhorn beetle
was found in the Boskoop, Netherlands, and
subsequently shut down the entire area,
which boasts the country’s most concentrated
collection of plant nurseries. In August 2010,
a citrus longhorn beetle was found in the
UK in the grounds of a primary school in
Oakham, Rutland. It was eventually traced to
a Japanese maple which showed evidence of
at least two beetle exit holes. UK plant health
inspectors said the tree was one of a batch
sold by a local wholesaler, originally sourced
from an Italian supplier.
We got away with it last time, probably
because this warmer-climate insect pest
did not have the right conditions to take off
and spread in the UK. But if climate-change
predictions are correct, the UK could offer
increasingly favourable conditions for the
next time citrus longhorn beetle arrives on
planting material from abroad.Left: Japanese maple
does not react well
to excess nitrogen so
nitrogen-based lawn
fertiliser should not be
applied in the vicinity of
trees growing in turf.Left below: Spring-time
and new foliage on
purple-leaved cultivars
contrasts starkly and
beautifully with verdant
greens of oak and other
native broadleaf trees.Below inset: Japanese
maple branches are
inherently slow growing
and therefore an ideal
site for epiphytic lichen
growth, shown here.