“HOODAH THUNKITT??”

That
could
have
summed
up
my
reaction
a
few
weeks
ago,
when
I
heard
Ryan
Neil
say
that

trees
and
shrubs
photosynthesize
through
their
bark
as
well
as
their
foliage.
They
don’t
photosynthesize

as
much

through
their
bark,
but
they
still
do
it.
This
has
a
number
of
implications
for
fall
and
winter
care
of
temperate-zone
trees.

(Readers
of
the
Fort
Wayne
Bonsai
Club
newsletter
has
already
seen
this
in
my
latest

Stuff
from
Steve.
)

First,
a
little
botany
review.
At
some
point
in
late
summer
or
fall,
temperate
species
stop
producing
new
foliage
and
direct
all
their
resources
to
two
purposes:
producing
more
vascular
tissue
(bulking
up),
and
storing
carbohydrates

sugars
and
starches

for
the
following
spring’s
growth
push.
Just

when

they
make
the
transition
varies
from
species
to
species;
for
example,
some
maples
(Acer)
switch
over
as
early
as
late
July,
while
Austrian
pine
(Pinus
nigra
)
does
so
in
early-to-mid
September.
But
they
all
make
that
shift.

Inside
every
plant
cell
is
a
structure
called
a

vacuole,
enclosed
in
a
semipermeable
membrane.
Some
plant
cells
have
more
than
one,
and
fungi
and
some
microorganisms
also
have
vacuoles.
However,
to
keep
this
discussion
simple,
I’m
going
to
stick
to
a
scenario
of
a
plant
cell
with
one
large
vacuole.
Here
is
a
diagram.
Notice
that
the
vacuole
can,
and
often
does,
take
up
more
than
half
the
space
inside
the
cell.

“V”
marks
the
vacuole.

During
spring
and
summer,
the
vacuoles
in
temperate-zone
plants
contain
water
and
not
much
else.
But
as
the
growing
season
progresses,
sugars
and
starches
for
the
next
spring
are
stored
up,
dissolved,
in
the
vacuoles.
At
first
only
what
is
left
over
from
foliage
production
and
other
metabolic
needs
is
stored.
Once
the
plant

for
our
purposes
a
bonsai
or
bonsai-in-the-making

makes
the
late-season
switchover
described
above,
carbohydrates
storage
goes
into
high
gear.

And
while
stored
in
the
vacuoles
waiting
for
spring
(for
any
who
may
not
know)
those
carbohydrates
serve
another
function:

antifreeze
!
Water
that
contains

anything

else
in
solution
freezes
at
a
lower
temperature
than
pure
water

sea
water
freezes
at
29
degrees
F
(1.6
degrees
C),
for
example.
And

the
greater
the
concentration
of
solutes
in
the
water,
the
lower
the
temperature
at
which
it
freezes
.

Trees
and
shrubs
continue
to
produce
and
store
photosynthates
as
fall
progresses.
That’s
true
for
deciduous
trees,
even
after
leaf
fall,
as
well
as
for
conifers,
because
of
the
aforementioned
photosynthesis
in
the
bark.
Production
and
storage
slow
down
as
temperatures
drop
and
day
lengths
shorten,
but
they
don’t
stop.
In
fact
those
processes
don’t
stop
altogether
even
when
ambient
temperatures
are
well
below
freezing
because
of
residual
heat
inside
the
tree’s
tissues.
It’s
true
that
for
all
practical
purposes,
trees
can
be
considered
dormant
at
temperatures
below
42
degrees
F
(5
degrees
Celsius);
but
carbohydrate
storage
in
the
vacuoles
continues
past
the
winter
solstice,
albeit
at
a
very
low
level.

Remember
that
the
higher
the
concentration
of
dissolved
substances
in
water,
the
lower
the
temperature
at
which
that
water
freezes.
This
means
that
as
fall
goes
along
and
more
and
more
dissolved
carbohydrates
are
stored
in
a
tree’s
cells,
the
more
cold-resistant
that
tree
becomes
and
the
deeper
the
cold
required
to
kill
it.
As
a
matter
of
fact,
the
strengthening
of
the
tree’s
cold-hardiness
stays
pretty
closely
in
step
with
the
falling
temperatures!
Temperatures
around
here
in
mid-December
are
colder
than
in
mid-October
(all
else
being
equal),

but

by
December
the
tree
has
more
“antifreeze”
stored
up
in
its
cells
than
it
had
in
October.
Temperatures
in
the
northern
hemisphere
usually
bottom
out
in
mid-January
(give
or
take
a
bit)
and
by
then
carbohydrate
concentration
in
the
vacuoles
has
reached
its
strongest.
(To
me,
the

elegance

of
the
whole
setup
demonstrates
the
sheer
skill
of
the
Creator.)

What
does
this
mean
for
fall
and
winter
care
of
bonsai
and
bonsai-in-the-making?

First,
if
a
tree
needs
any
fall
pruning
or
working,
do
it
as
soon
as
possible

after

the
transition
away
from
foliage
growth
has
begun;
make
sure
not
to
do
it
before
that.
You
want
the
tree
to
have
as
much
time
as
possible
to
heal
over
the
trauma,
but
you
also
don’t
want
to
interfere
with
production
of
leaves
and
needles

primary
photosynthesizing
surfaces

until
that
production
stops
naturally.

Second,
keep
up
light
fertilizing
through
the
fall,
and
even
(very
light)
into
early
winter.
The
tree
will
still
benefit
by
it.
And
the
same
goes
for
water:
keep
the
soil
at
least
moist
unless
and
until
it
freezes.
(For
any
who
don’t
know,
freezing
won’t
harm
a
temperate
tree’s
roots;
neither
will
staying
unfrozen.
But
do
try
to
avoid
alternating
freeze-and-thaw.)

Third,
and
contrary
to
some
conventional
wisdom,
it’s
best
to
give
all
your
trees

some

light
throughout
the
cold
months,
even
your
deciduous
ones.
Remember
that
they
can
photosynthesize
through
the
bark.
At
the
same
time,
if
you
can’t
give
your
deciduous
trees
any
light
during
the
winter,
you
won’t
lose
them
as
long
as
you
can
keep
them
below
42
degrees
F
(5
C.).
They
just
won’t
get
off
to
quite
as
strong
a
start
in
the
spring.

One
more
thing:
please
remember
that
all
of
this
applies

only

to
temperate-zone
trees.
Tropicals
are
another
ball
of
wax

or
should
I
say
“of
bark”?


🙂
🙂
🙂

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