The “droops of summer” have come early this year.
As water deficits become
greater in the landscape, remember that both old and young
trees need your help. A few
deep waterings can help minimize damage and may save a tree’s
life.

Water is the stuff of which tree life is made. Trees use
water for transporting
materials, chemical reactions and supporting growth. Water
solutions allow all of the
tree’s living processes to function properly.

As water becomes less available, trees begin to have
problems. One of the first
noticeable signs that trees are short of water is leaf
wilting.
On sunny, hot days, leaves
lose water faster than roots can absorb it. As leaves lose
more
water, they begin to
droop.

Leaves Hanging Limp

If you go out in the afternoon and look at your trees,
leaves across whole crowns or on
individual branches may be hanging limp. By early the next
morning, the leaves will be
back to normal. Refilling with water overnight means the tree
can still extract water from
the soil.

Wilted leaves that don’t recover overnight signify serious
water shortages in the soil.
Leaves that stay wilted for three days or more are being
severely damaged.

Usually, permanently wilted leaves yellow and die quickly.
Sometimes, small amounts of
water may keep these leaves hanging on to life (and the tree)
even though they’re
sustaining long-term damage.

Woody cells don’t change shape much, even when dry. Whole
trees don’t change shape or
wilt. Succulent new twigs and annual leaves supported by their
thin petioles can droop
severely. Water expands thin-walled cells. Without water to
maintain the cells’ size, they
shrink or collapse.

Receding Cell Walls

As some leaf cells shrink, their walls pull inward. Each
cell shares a wall with a
neighboring cell. As one leaf cell shrinks, it pulls other
cells closer. As all cells
shrink, leaf tissues may appear deformed and shriveled. The
leaf stalk, or petiole, on
many deciduous trees can quickly lose water, which allows the
leaf blade to droop.

Many evergreen trees, like pine, have strong fibers and
heavy veins which prevent
noticeable wilting. Needles may curl but stay in position.

Many deciduous trees hold their leaves erect in sunlight,
but fold and droop under
water shortages. The act of wilting can help minimize further
water loss from the leaves.

For leaf expansion in spring, many new cells were outfitted
for life. Each new cell’s
wall was thin and flexible, like a balloon. In order to grow,
the cell must expand its
wall.

Trees’ ‘hydraulic fluid’

Water is the hydraulic fluid a tree uses to “blow up
the balloons” of its
cells. Each cell uses nutrients shipped from other cells to
help it collect water.

Cells draw water to surround many kinds of materials with a
shell or layer of water
molecules. The more surface area in individual pieces of
nutrients (like sugar) a cell
has, the more water it attracts.

The more water a cell can contain, the higher the water
pressure becomes, and the thin
cell walls expand outward. The cell begins to grow. Finally,
the cellulose strands in the
cell’s wall stop further expansion, and a “glue” is
deposited around the wall to
hold everything in its new, expanded shape.

If water isn’t available, tree cells can’t grow. If the
cells dry too much, the new
walls may collapse inward. One symptom of severe drought
damage
is small, stunted and
deformed leaves.

Keep an eye on your trees. Don’t let the “droops of
summer” cause permanent
damage.

For more information on trees, droughts and watering, visit
the University of Georgia
School of Forest Resources Web site at: www.forestry.uga.edu/efr
/
.