Educational
Resource Guide #301 
Turfgrass During Drought
by Don Janssen, Extension Educator
The
primary turfgrasses grown in home lawns are cool season grasses.
The most common species of cool season grasses used in residential
lawns include Kentucky bluegrass, perennial ryegrass, fine fescue
and tall fescue. Cool season grasses perform best when daytime
temperatures are in the range of 60 to 75 F along with 1-1.5
inches of water per week. These lawns possess the best color
and quality attributes during the spring and fall seasons. Being
cool season grasses, good to excellent winter hardiness allows
established lawns to survive even the harshest winters.
The
most stressful time of the year for cool season grass is typically
in the summer (i.e., June through August). This period is often
characterized by hot, sunny days with daytime temperatures routinely
in the mid 80's to low 90's ( F) . In addition to high temperatures,
moderate to severe moisture stress is often imposed on the turfgrasses.
The combination of high temperatures and dry soils will lead
to significant declines in turfgrass quality unless proper management
practices are implemented.
Turfgrass
plants need soil moisture to sustain normal growth and development.
The water use rates of cool season turfgrasses during the summer
period will often exceed the rate which natural rainfall returns
water back into the soil. Once the soil moisture reserves are
nearly depleted, the turfgrass will begin to wilt and turn from
green to either bluish-green or gray-green. Wilt is a sign of
water stress and is usually most evident during mid to late
afternoon. The continual water stress that limits or prevents
the growth of plants is termed drought. Once drought conditions
develop, the lawn will stop all growth and development and proceed
into dormancy.
Dormancy
is characterized by the development of brown turfgrass. The
turfgrass is not dead but in a condition which preserves the
vital parts of the plant. Turfgrass dormancy reduces water usage
and can concentrate the limited amount of available moisture
into the crown, rhizomes and roots. This dormant condition will
allow the turfgrass plant to survive adverse conditions for
extended periods until soil moisture reserves are replenished.
The
length of time lawn grasses can survive in a dormant condition
is dependent on a number of factors including soil moisture
levels, daytime temperatures, condition of the turfgrass at
the onset of dormancy, etc. In general, turfgrasses can be expected
to survive in a dormant condition for up to four to five weeks
with limited damage if temperatures are at or below normal.
If daytime temperatures are high (mid-80's or higher) consistently
through the stress period, only three to four weeks of survival
can be expected. Dormant grass is lost once the crowns, rhizomes
and roots begin to dehydrate. The areas of the lawn along sidewalks,
curbs, driveways, south facing slopes, etc., will encounter
the most stress and will be the first areas to die during extended
periods of drought.
Homeowners
have little control over the daytime temperatures in the lawn.
However, they can improve the survivability of the turfgrass
in their lawn through proper management. This management includes
proper cultural practices and/or irrigation.
Proper
Summer Cultural Practices
The
ability of lawn turfgrasses to survive drought conditions is
improved if proper cultural practices are followed. The practices
should start in early June and continued until late August.
The most important cultural recommendations include:
Proper
Mowing
The
mowing height should be a minimum of 3.0-3.5 inches prior to,
and during, drought periods. Taller cut grass will have deeper,
more extensive root systems than short cut grass which will
help enable the turfgrass plants to withstand summer stresses.
Taller cut turfgrass will provide more shading of the soil thereby
keeping soil temperatures cooler and reducing evaporation of
soil moisture.
When
mowing the lawn never remove more than one-third of the total
leaf area at any one time. A lawn mowed at a height of 3 inches
should be cut when it reaches a height of 4.5 inches. Removing
more than one-third of the leaf area weakens the turfgrass and
reduces its capacity to withstand additional environmental stresses.
Weakened turf is also more likely to be invaded by weeds.
If
possible mow in the cool of the morning or evening. Mowing during
high temperatures of midday places additional stress on the
turf. Also make sure the mower blade is sharp. Dull blades tear
and bruise the leaf tips.
Lawn
Irrigation
Homeowners
following the recommended summer management practices need to
irrigate to prevent lawns from becoming dormant during dry periods.
Without rainfall, a lawn will normally require supplemental
irrigation of approximately 1.0 inch of water per week to keep
the lawn green.
The
amount of water applied during irrigation can be measured by
placing several empty straight-sided containers, such as pet
food containers or tuna cans, in the sprinkler's pattern. Stop
watering when the desired volume of water is collected in the
containers. Irrigation should be performed early in the morning.
At this time of day the temperatures are cooler, humidity is
high and calm wind conditions usually exist. These
conditions favor infiltration of the water into the soil and
the availability of the supplemental water.
When
the water supply for lawn irrigation is limited or when watering
restrictions are in place, the homeowner should designate priority
areas of the lawn and water those areas first. The priority
areas usually include the front lawn, areas around the patio
or deck, and children's play areas.
If
the homeowner cannot water, or elects not to water a dormant
lawn, a light watering or rainfall of 0.5 inch every two weeks
will help minimize damage to the lawn during the dormancy period.
This watering practice will supply enough moisture to keep crowns,
rhizomes and roots hydrated and alive. This volume of water
will not regreen a dormant lawn, however, it will help to insure
good recovery once rainfall occurs later in the summer.
Do
not fertilize the lawn, or try to control weeds, insects or
diseases during drought. Stay off the lawn as much as possible.
Just keeping the lawn alive is the most important thing to do
during drought.
This
Educational Resource Guide was updated on August 23, 2002
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