Dry spots after a Central Texas summer

If patches of your lawn stay brown no matter how long the sprinklers run, the problem is almost always where the water lands, not how long it runs. The US EPA's WaterSense program estimates that as much as 50 percent of the water used outdoors is lost to wind, evaporation and runoff caused by inefficient irrigation methods and systems, and a system that is not properly maintained can waste up to 25,000 gallons a year. In Central Texas that shows up in September as dry patches the homeowner has been watering harder all summer.

What does the shape of a dry spot tell you?

A dry spot is a map of your coverage. Walk the yard early in the morning and look at the outline of the brown rather than the brown itself. Four patterns account for most of what our crew finds on Georgetown-area properties.

Shape of the dry area	Usual cause	What to check
A long, narrow stripe running between two heads	The two spray patterns no longer overlap	Nozzle wear, or water pressure that has dropped
A circle with a hard edge, green right up to the line	A rotor that has stopped rotating, or a blocked nozzle	Watch the head while the zone runs
A wedge cut out of an otherwise green circle	The arc has been knocked out of adjustment	Heads along mowing lines and bed edges
Dry right at the head, green further out	The head has sunk, or grass has grown over it	Head height against the soil line

How do you check a sprinkler zone?

Put the controller in manual, run one zone at a time, and stand in the yard rather than watching from a window. Write down what each zone does: heads that do not pop up, heads that pop but do not turn, water pooling on the sidewalk, and spray that looks like fog instead of droplets. Fog means pressure is too high for the nozzle, and much of that water leaves as the evaporation and drift the EPA figure above is describing.

How do you run a catch can test?

Texas A&M AgriLife's Water University publishes the homeowner version of an irrigation audit. Their instructions are to place 5 to 9 catch cans in each zone, tuna or cat food cans being the usual choice, then run spray zones for 5 minutes and rotor zones for 10 to 15 minutes and measure what collects in each can.

What matters is the spread between the cans, not the depth in any one of them. Texas A&M's standard is simple: if the levels are equal or near equal, the system is applying water evenly. A can holding a quarter inch beside one holding an inch is a coverage problem, and no amount of extra run time fixes it, because you would have to flood half the zone to get water onto the other half.

The same guide shows how to turn the reading into a schedule. A quarter inch collected in 5 minutes means roughly 20 minutes to apply an inch.

Why does watering longer not fix it on clay soil?

Because our soil cannot absorb water as fast as a sprinkler applies it. AgriLife Extension's cycle and soak guidance (publication AGEN-PU-218) notes that fine textured soils such as clays have low infiltration rates, so water applied past that rate runs toward the curb instead of soaking in.

The fix is to split the run into shorter cycles with a soak between them. AgriLife puts the gap at 30 to 60 minutes, and states that heavy soils like clay usually need at least 60 minutes between cycles for best retention. Their worked example splits a 45 minute run into three 15 minute cycles. This is the single most common scheduling mistake we correct on Central Texas properties.

When is it not the sprinklers?

Some dry patterns have nothing to do with water. Chinch bugs are the one to rule out first in St. Augustine. AgriLife Extension's Travis County office notes that chinch bugs favor hot spots of the lawn such as next to driveways and sidewalks, that the damage appears as expanding irregular patches, and that a halo of yellowing to orange grass often shows at the outer edge of the dying area. That halo is the tell, and it takes only 22 to 25 chinch bugs per 1,000 square feet to cause damage.

Mowing height is the other one. AgriLife's St. Augustinegrass guide (EHT-144) puts the maintained height at 2 to 4 inches, advises removing no more than one third of the green canopy at a time, and notes that a taller mowing height gives deeper rooting and improved water infiltration. A lawn cut short all summer roots shallow and gives up early in the heat, which looks like a watering problem and is not one. Both of those are lawn treatment questions rather than irrigation ones.

When should you fix coverage?

September and October are the window in Georgetown and the surrounding area. The ground is still warm enough that corrected coverage does the turf some good before dormancy, and the same visit that adjusts heads and nozzles is the one that prepares the system for winter. Waiting until spring means an uneven green-up and chasing patches that were fixable in the fall.

There is a business case as well as a lawn one. WaterSense estimates that a system managed properly by a certified professional uses about 15 percent less water, close to 7,600 gallons a year for an average household. Our irrigation maintenance service covers the zone-by-zone check, the head and nozzle corrections, and the seasonal schedule, and we would rather adjust four heads in September than replace dead turf in April.

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