Quick Facts...
- In Colorado, Kentucky bluegrass, tall fescue, and perennial ryegrass
lawns must receive supplemental irrigation to survive.
- Soil preparation is critical to the rooting depth and drought tolerance
of turf.
- Kentucky bluegrass lawns may require 2.5 inches of water or more per
week during the heat of summer.
- The best time of day to irrigate is between 10 p.m. and 6 a.m.
- Lawns grown on sandy soil require more frequent
irrigation applications (with less water per application) than lawns
grown on clay soil.
To determine the most appropriate irrigation schedule for an established
lawn consider the following: turf species; soil type; cutting height;
potential disease and pest problems; local weather patterns; and microclimates
(i.e., shade vs. full sun exposure; low vs. high areas of the yard). For
example, a lawn cut at 3 inches holds water longer than a lawn cut at
2 inches; or lower areas of a lawn hold water longer than higher areas.
A properly designed and installed automatic sprinkler system should be
programmed to accommodate these specific lawn needs. Rain sensors are
useful for residents who are unable to adjust automatic systems when rainfall
occurs.
When designing an irrigation system and developing an irrigation schedule
consider the presence of trees and shrubs in the lawn because they have
roots in the turf area that compete for water and nutrients. Take care
to avoid root damage when installing a sprinkler system in areas with
established trees and shrubs. For more information see fact sheet 2.926,
Healthy Roots and Healthy Trees.
A lawn’s tolerance to drought is directly related to how well the
soil was prepared prior to applying seed or sod. Heavily compacted soil
that is low in organic matter does not facilitate deep, healthy root growth.
Grass roots grow to their maximum depth in well-aerated soil containing
four to five percent organic matter. A healthy, deep root system produces
vigorous turf that is tolerant of drought and resistant to disease and
insect pests.
In Colorado, cool season turfgrass such as bluegrass, fescue, perennial
ryegrass, or bentgrass needs regular applications of water. And even though
warm season grasses (blue grama and buffalograss) are known for their
drought tolerance they too thrive with occasional watering. The condition
of the grass and soil – not the number of days since watering –
is the best guide to irrigation. If you water daily or every other day,
just because water is available, it is a waste of water and can be detrimental
to the lawn. Doing this can predispose the turf to disease. Watering too
frequently causes root death of trees and shrubs in or near the turf area
either from root rot disease or lack of oxygen in the soil. Amount and Frequency of Application
The rule of thumb for watering an established lawn is, “water as
deeply and as infrequently as possible.” Deep and infrequent irrigation
stimulates root growth, resulting in healthy, drought tolerant, and pest
resistant turf. While it’s true that a deep, healthy root system
produces vigorous turf, rooting depth is determined primarily by genetics
and soil condition – not irrigation. Maximum rooting depth occurs
when soil conditions allow the roots of a particular species (or variety)
to reach their full potential. This is not achieved by proper irrigation
alone; a combination of proper irrigation, proper fertility (see fact
sheet 7.202, Lawn Care), and regular core aerification (once in
spring and/or once in fall) maximizes rooting depth and overall turf vigor.
Amount
Apply 1 to 1.5 inches of water per irrigation. Determine how long this
takes by setting several shallow containers (such as baking pans) in different
areas of the lawn for thirty minutes while irrigating. Measure in inches
the depth of water in the containers. The average depth of water in these
containers multiplied by two is the inches of water per hour emitted by
the sprinkler system.
Clay soils (which include most Colorado soils) have a much lower penetration
rate than sandy soils; therefore, clay needs to be watered at a slower
rate in order to avoid runoff and puddling. To avoid runoff from very
heavy clay soil and/or a sloped lawn you can water for a short period,
then stop and start back up again until 1 to 1.5 inches of water has accumulated.
Most irrigation clocks permit this type of cycling feature.
Water pressure varies from one location to another thus the length of
time a neighbor waters may not necessarily be appropriate for your lawn.
Lawns also have different soil types which permit water infiltration at
different rates. Experience will eventually turn this seemingly tedious
process into one that is quick and second nature.
Frequency
Irrigate when the turf indicates water is needed. Look for signs of wilt,
which often show up in the same location on the lawn time after time.
Footprints or lawn mower tracks that remain at least one half hour after
traffic has passed indicates irrigation is needed. Turf will also turn
a shade of blue-gray when it is water stressed and in need of irrigation.
Do not irrigate again until you see signs of wilt. It’s important
that the soil profile dries somewhat between irrigation applications.
Continually water-logged soils are deprived of oxygen which is required
for proper root growth.
On very hot days turf may appear stressed even if the soil is wet. This
is caused by heat stress and can be remedied by cooling off the turf by
wetting it for 15 seconds or less. This technique is called syringing
and is not the same as watering.
Time of Day to Irrigate
The best time to irrigate your lawn is between 10 p.m. and 6 a.m. During
this period it is generally cooler, less windy, and the humidity is higher
so evaporation losses are less. Water pressure may also be higher at this
time providing a more even spray distribution pattern.
Irrigating between 10 p.m. and 6 a.m. also overlaps with the turf’s
natural dew period. Most diseases of turf occur when grass blades are
wet for longer than 14 consecutive hours. Watering before 10 p.m. or after
6 a.m. extends the natural wetness period and increases disease problems.
Dew contains substances exuded from the plant tissue. These materials
increase the growth of disease organisms. Water applied between 10 p.m.
and 6 a.m. dilutes these materials thus reducing the growth of turf disease
organisms.
If it is not practical to water during this time period, another option
is to water between 9 and 11 a.m., starting the irrigation after the dew
has dried but before the winds begin. From a disease prevention perspective,
irrigating anytime between 9 a.m. and 4 p.m. is fine (as long as the turf
dries before the evening dew period sets in); however water loss from
sun and wind will be greatest at this time.
Winter Watering
Winter watering may not be necessary for established lawns. However, lawns
started within the last year are especially susceptible to winter dessication
injury and need supplemental winter irrigation. Areas of Colorado which
experience open, dry winters are more susceptible to winter grass mites
and dessication if occasional winter irrigation is not applied. See fact
sheet 7.211, Winter Watering for more information.
Additional Information
For
more information, see the following Planttalk
ColoradoTM script(s).
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