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Field maple (Hedge maple) - Acer
campestre
General infomation:
Simon and Shuster's guide rates this
tree as very easy to cultivate as bonsai. Like the Montpelier
maple, the lobes of its leaves are obtuse, otherwise uncommon
in maples. Its branches don't seem to ramify as finely as other
maples. It is a pleasing display tree in autumn, with buttercup
yellow leaves. In the wild, the tree grows to 30 to 35 ft., but
it grows slowly. A dwarf version, "Compactum," only
grows to 6 ft. and is commonly used for hedges. The most desirable
cultivar is A. campestre 'Compacta,' a dwarf variety with leaves
half the size of the species. Hedge Maple is usually low-branched
with a rounded form, but there is considerable variability from
one tree to the next. The branches are slender and branch profusely,
lending a fine texture to the landscape particularly during winter.
Family: Aceraceae
Lighting:
Unlike most maples, the field maple responds well to direct sunlight.
Temperature:
Hardy in zones 5-8. Small bonsai should be frost protected in
winter.
Watering:
Moderate, although if kept in full sun, care must be taken to
insure that the soil never dries out completely. Reduce watering
in winter, but keep soil evenly moist.
Feeding:
Every two weeks in summer, using a standard bonsai food or half-strength
plant food. Time-released pellets are also an option.
Pruning and wiring:
The field maple is easy to style by judicious pruning, as the
scars heal quickly and well. It is necessary to prune often to
avoid long internodes. Buds back excellently. Wiring should be
done on newly hardened branches, as older, thicker branches tend
to become stiff. The field maple responds well to a yearly leaf
pruning in June, and responds best to wiring if done directly
after leaf pruning. With diligent pruning, the leaves can be
reduced to below an inch. For medium to large bonsai, this tree
can be field grown to reach trunk diameters of two inches or
larger.
Propagation:
From seed, after a three month cold treatment, and also from
softwood cuttings or air-layering.
Repotting:
The field maple is a fast growing tree, and should be repotted
at least every two years. Repot in spring, before bud burst,
in basic bonsai soil. Soil tolerances includes: clay; loam; sand;
acidic; alkaline; well-drained
Pests and diseases: Pests: Leaf stalk borer and petiole-borer cause the same
type of injury. Both insects bore into the leaf stalk just below
the leaf blade. The leaf stalk shrivels, turns black, and the
leaf blade falls off. The leaf drop may appear heavy but serious
injury to a healthy tree is rare. Aphids infest maples, usually
norway maple, and may be numerous at times. High populations
can cause leaf drop. Another sign of heavy aphid infestation
is honey dew on lower leaves and objects beneath the tree. Aphids
are controlled by spraying or they may be left alone. If not
sprayed, predatory insects will usually bring the aphid population
under control. Scales are an occasional problem on maples. Perhaps
the most common is cottony maple scale. The insect forms a cottony
mass on the lower sides of branches. Scales are controlled with
horticultural oil sprays. Scales may also be controlled with
other well-timed sprays to kill the crawlers. If borers become
a problem it is an indication the tree is not growing well. Controlling
borers involves keeping trees healthy. Chemical controls of existing
infestations are more difficult. Proper control involves identification
of the borer infesting the tree then applying insecticides at
the proper time.
Diseases: Verticillium
wilt symptoms are wilting and death of branches. Infected sapwood
will be stained a dark or olive green but staining can't always
be found. If staining can not be found do not assume the problem
is not verticillium wilt. Severely infected trees probably can't
be saved. Lightly infected trees showing only a few wilted branches
may be pulled through. Fertilize and prune lightly infected trees.
This treatment will not cure the problem but may allow the tree
to outgrow the infection. Girdling roots will cause symptoms
which mimic verticillium wilt. Tar spot and a variety of leaf
spots cause some concern among homeowners but are rarely serious
enough for control.
Bibliography:
The Simon and Schuster Guide
"Complete Book of Bonsai," by Tomlinson
"Miniature Bonsai" by Gustafson
"Bonsai" by Resnick
USDA Fact Sheet ST-10
Compiled by Sabrina Caine
Edited by Thomas L. Zane
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