American Red Maple - Acer
General Information: Also called Swamp Maple, A. rubrum in nature is a tree,
60 to 75 feet tall. Young trees are often pyramidal or elliptical and are
fast growers with strong wood. Older trees develop ascending branches,
resulting in an ovoid or rounded crown. There is ample evidence to
suggest that trees native to a specific area are more likely to be hardy
there. Tolerates ozone and is somewhat tolerant of sulfer dioxide, making
it a good tree for urban areas.
Leaves are opposite, 2 to 4 inches, quite variable in
shape, 3-5 lobes, dullish green, with reddish leafstalk. They
turn brilliant red, orange and yellow in fall.
Lighting: Full sun to
rubrum prefers wet to moist soils.Water copiously during the
warm months, especially if the soil does not hold water. In hot climates
keeping the tree in a shallow tray of
water may be necessary.
Fertilize weekly, beginning in early spring; bi-weekly in fall until
leaves begin to turn.
Pruning and wiring: A. rubrum can be styled as informal upright, slanting,
clump, group and forest. I have never grown A. rubrum as a cascade
or root-over-rock, since neither represents its "natural" growing
The bark of A. rubrum (as other maples) is
tender and scars easily. On the rare occasion that I do wire, I
use unstripped aluminum wire. Since the natural growth habit of A.
rubrum is to have ascending branches, forming a generally oval shape
with a rounded top, wiring to pull down branches is not
Wires must be watched carefully. Even rubber-coated
aluminum wire will scar before a summer has passed.
Pruning is the primary means of shaping A.
rubrum. Pruning and leaf trimming can be used to increase the
ramification of twigs, to induce branches to grow where none grow now, and
to create valuable open spaces.
Trim new growth by allowing one or two nodes to grow,
then pinching back to one. The more frequent and more severe the pinching
back, the shorter the distance between the leaves and new branch
Major pruning should be undertaken with
care. A branch, once removed, is difficult to replace. Although you might
be able to induce sprouting at the site of the scar, the resulting branch
will be thin and awkward looking. In the case of major branch removal,
A. rubrum will repair pruning scars quite well if the cut is made
flush with the trunk.
A. rubrum will endure
leaf stripping (complete removal of leaves), but leave the leaf stem
attached (it will fall off when new leaves appear). You also may cut
leaves in half. I have seen no benefit from partial leaf stripping
(stripping leaves from selected areas of the tree in an attempt to develop
better twig and branch structure).
Propagation: Seed germination Up to 60%.They also
propagate easily from cuttings.
Small specimens may be bare rooted for transplant. Larger specimens must
be balled and burlapped in order to be moved.
Potting and root pruning should be done in spring, as
leaf buds turn a brighter red. This tree, when mature, is quite hardy and
will suffer severe root pruning to no disadvantage that I can see.
(However, I would not strip leaves in the same year as the severe root
pruning.) Since this is a tree of usually wet to damp soils, the tap root
is not well developed.
Root pruning probably should be done every other year
on a mature maple, but the amount of annual root growth will vary,
depending on conditions, the pot, fertilization schedule, watering regime,
and the individual tree. Younger trees and seedlings-in- training may be
root pruned annually.
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.
Gall mites stimulate the formation of growths or galls on the leaves. The
galls are small but can be so numerous that individual leaves curl up. The
most common gall is bladder gall mite found on silver maple. The galls are
round and at first green but later turn red, then black, then dry up.
Galls of other shapes are seen less frequently on other types of maples.
Galls are not serious, so chemical controls are not needed. Crimson
erineum mite is usually found on silver maple and causes the formation of
red fuzzy patches on the lower leaf surfaces. The problem is not serious
so control measures are not suggested. 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 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 usually controlled
with horticultural oil sprays. Scales may also be controlled with
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. Twig borers can
cause die-back of the terminal 8 to 12 inches of small-diameter branches.
This is usually not serious and does not require control measures, but it
can be a problem on young trees in the nursery.
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