During the growing
season water is constantly moving into and out of a plant. The
water moves out from the foliage as water vapor is replaced with
water from the soil. Water moves into the roots and up into the
plant through the vascular system. During a warm summer day a
slight water deficit exists within the plant as more water moves
out than in. During the night the deficit is corrected and a water
balance restored. During periods of drought, there is insufficient
water in the soil and a prolonged water deficit occurs.
Since a plant cannot
add more water to the soil, it tires to restore the water balance
by reducing water loss. Initially the foliage wilts and the leaf
stomates, the opening through which water vapor is lost, close.
This reduces water loss but at the expense of photosynthesis.
Plants rely on photosynthesis not only to make enough food to
sustain themselves each day, but also to create a reserve food
supply that is used to create the buds that will persist through
the winter and begin growth the following spring. Any prolong
drought will reduce the amount of food produced and stored by
photosynthesis. Reduced food storage threatens the plants ability
to grow normally the following spring.
Severe Droughts
If the drought is severe
plant tissues fail. This manifests itself in foliage drop and
small twig and branch die back. However, the real damage occurs
beneath the ground. First there is a rapid loss of root hairs.
These roots are rather ephemeral and are constantly being lost
and regrown. As the drought continues the fibrous roots system
begins to fail. These roots are very important because they are
the roots that are necessary to produce the new root hairs. If
a substantial number of fibrous roots die, the plant will have
difficulty resuming normal growth the following year.
Rapid Spring Failure
As the weather warms
in the spring, plants break dormancy and begin to grow. Buds open
and new stem tissue grows and produces new leaves. If the weather
is average and there is sufficient soil moisture and there is
a sufficient stored food reserve, the plant will grow and develop
normally. If however, any of the above factors are not favorable,
the plant will be in trouble. Some plants may exhibit less growth
than normal, or they may lose some of their existing growth. Sometimes
the plant may put out a good spring flush of growth and then collapse
and die. It simply depleted all available energy, a sad result
of the past year’s drought.
Prevention is the Only Cure
Drought damage can’t
be fixed but it can be prevented. Urge your clients to review
their landscapes and select those plants they consider priority
plants. When the next summer drought occurs urge them to initiate
an irrigation program for those priority plants. In ground irrigation
systems are best, but in a pinch a few hundred feet of hose can
spell the difference between healthy growing plants the following
spring and a lot of chain saw maintenance.
