1 irrigation cycle
recommended per week, during the Spring and late Fall
2 Irrigation cycles recommended per week, during the
3 Irrigation cycles recommended per week, Mid - Late
Summer or when drought conditions exist or if
on a hillside or slope
Check the index once a week on the first of your assigned watering
days. The "weekly watering amount" shown is the amount needed over the
next 7 days. If you're watering only once
a week, apply that entire amount then. If you prefer to water twice a
week, apply half the watering amount on each day.
What do all these numbers mean?
These numbers show various weather data that help determine how
much water your lawn really needs. High and low temperatures
are just two of the factors used to calculate the potential evapotranspiration amount, shown here as "ETo." You can think of ETo
as the amount of water a plant would need if left constantly exposed
to the sun, above the ground. Since most plants are actually in soil
and have varying amounts of sunlight throughout the day, we apply
stress coefficents for an average St. Augustine lawn in Austin to
determine the ET Index.
What is evapotranspiration?
Evapotranspiration is a measurement of the total amount of water
needed to grow plants and crops. This term comes from the words
evaporation (i.e., evaporation of water from the soil) and
transpiration (i.e., transpiration of water by plants). The equation
used to determine potential ET (ETo) considers a large number of
weather factors like wind, temperature, dew point, humidity, and
If we know how much water is lost each day, why don't we water
Allowing your lawn to dry out between waterings actually encourages
a deeper root structure -- the grass has to look deeper in the soil
for the water it needs. Plants with deeper roots are better able to
withstand drought, harder to uproot, and can be more resistant to
disease. Plus, the daily ET amounts for Austin are usually very small.
Most automatic irrigation systems can't be adjusted to water less
than 1/4" with each operation, so it would be next to impossible to
apply only a tenth of an inch daily.
How do I know when I've watered enough?
Set empty tuna or cat food cans at intervals around your lawn and
garden. Turn on your sprinkler for 15 minutes. Measure the amount of
water in the cans. Now that you know how much water your sprinkler
puts out, you can figure out how long to leave it running when it's
time to water.
Example: After 15 minutes of running your sprinkler, you have an
average of 1/4" in your tuna cans. When the ET Index is 1/2" (and you
haven't had any rain), you should run your sprinkler for 30 minutes.
For an ET of 1/3", you'd run the sprinkler for about 20 minutes.