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Sweet Acacias
are popular and
well-adapted shade trees
for arid region
landscapes. Fragrant
flowers, upright stature
and rapid growth rate
makes it desirable for
commercial and
residential landscapes.
It is used as a theme
tree in streetscape
planting or at
development entries but
is probably used most
often as individual
accent trees in mixed
desert planting. Most of
the literature reports
that trees mature to a
height of 15’ to 30’.
Our experience has been
that trees may reach 35’
to 45’ and may be 30’
wide.
Mature trees
are best adapted to full
sun, well draining soils
and infrequent deep
irrigation. They
tolerate both desert and
lawn plantings. Standard
and multiple trunked
specimens are equally
popular. Rapid tree
growth coupled with the
tendency of this tree to
produce new branches all
along the trunk make
regular, moderate
pruning a maintenance
must.
Leaves are
made up of 10 to 20
pairs of tiny oval
leaflets giving the leaf
canopy a delicate,
fern-like appearance.
Unpruned mature trees
provide fairly dense
shade and inhibit the
growth of flowering
understory plantings.
Sweet acacias are
semi-deciduous. In
warmer winters or in
certain microclimates
trees may retain a
majority of the leaf
canopy. Leaves are shed
in spring with the
resumption of new
growth.
Bloom period
seems to be somewhat
variable depending on
the severity of winter
cold temperatures. In
years with mild fall
weather flower buds may
appear on some trees in
November and December
with blooms persisting
into late winter and
early spring. Other
specimens may not begin
blooming until mid to
late spring with flowers
lasting until April to
late May. Mature seed
pods are dark brown,
cylindrical, 2 to 2 1/2
long and 1/4 to 3/8" in
diameter.
TAXONOMY
Plant taxonomy is the
science of organizing
plants into established
categories and giving
them names (a Latin
binomial), based on
their characteristics.
Originally this tree was
called Acacia farnesiana
after the 17th century
Roman Cardinal Odoardo
Farnese. Since the late
1960’s plant taxonomists
have been troubled by
the wide variety of
horticultural
characteristics
(flowering periods, cold
hardiness etc.)
exhibited by Sweet
Acacias. In 1969 it was
proposed that Sweet
Acacias actually
represented two
different tree species.
Acacia
smallii was proposed as
the name for all the
Sweet Acacias occurring
from
California
to western most
Florida and Acacia
farnesiana for those
trees found in the
balance of
Florida
and the
Caribbean.
The horticultural
characteristic of
greatest interest to
landscape professionals
in the desert southwest
is cold hardiness.
Experience over the last
10 to 15 years has shown
that Acacia farnesiana
is severely (sometime
fatally) damaged by
temperatures below 20
to 25 degrees F. In contrast
Acacia smallii
appears hardy to about
15 to 20 degrees F.
and survives most
central and southern
Arizona and southern
California winters
injury free. While there
are other physical (tree
structure) and botanical
distinctions between
these two species the
greater cold hardiness
of Acacia smallii is of
most interest to
landscape professionals.
Arid Zone Trees
distributes Sweet
Acacias in Arizona,
Nevada and California.
The various communities
within these states
experience different low
temperature extremes in
any given winter. As a
result we only grow
Acacia
smallii, and we
constantly are looking
for selections to
propagate that have
exhibited the highest
levels of cold hardiness
that we can identify.
Cultural Practices:
Foster the development
of a more dispersed root
system and reduce the
risk of wind throw by
arranging irrigation
emitters at varying
distances from the trunk
to encourage roots to
"seek out" water and
nutrients. Irrigation
emitter arrangement
along with other
information on
irrigations practices
for desert trees can be
found at
www.aridzonetrees.com
and click on the FAQ
link.
Prune as needed to
reinforce the structure
and form of the tree.
Periodic thinning is the
most desirable method of
pruning. Avoid hedging
or heading back desert
species, as this will
only stimulate excessive
branching. Do not remove
more than 30% of the
canopy during the summer
as this can lead to
sunburn injuries that
can later be invaded by
wood boring insects.
Always use clean, sharp
tools that are cleaned
regularly in a 10%
solution of bleach. For
detail pruning guide see
www.aridzonetrees.com
and click on the FAQ
interactive button.
Periodically
insect pests can be a
problem on some desert
trees. On young trees,
insect infestation can
slow typical seasonal
growth. Inspect trees
during the growing
season for common garden
sucking insects such as
aphids, thrip,
whiteflies or psyllids.
During dry months, (May
and June) in dusty
conditions, spider mites
can appear. Monitor for
infestation and apply
controls as needed.
Spray applications of
water or water and Safer
Soap give short-term
control (3 to 7 days)
for small insect
population. For heavy
infestation or longer
control use federally
registered insecticides.
A contact insecticide
application will kill
existing adults. An
application with a
systemic soil drench
will provide 8 to 12
weeks control for any
post application insect
hatchings or migration
of insects. Before using
pesticide for the first
time or on new plants or
cultivar, treat a few
plants and check for
phytotoxicty.
Always read label and
follow label instruction
before using pesticides.
For pesticide control
recommendations contact
a
licensed pest control
advisor.
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