The Irrigation Audit: Finding Out What Your System Is Actually Doing

A great many lawn problems that get treated as pest, disease or nutrition problems are actually water distribution problems. The lawn is not sick — parts of it are simply not getting watered.

The catch-can test

This is the whole audit and it costs nothing.

1. Put identical straight-sided containers — tuna cans work perfectly — across a zone in a grid, including near heads and midway between them.
2. Run that zone for a set time. Fifteen minutes is a reasonable test.
3. Measure the depth in each container.
4. Compare. If some containers have twice what others do, you have a distribution problem, and no run time will water the whole zone correctly.

Repeat for each zone. It takes an afternoon and it will explain most of the mysterious patches in a lawn.

What causes uneven coverage

• Heads out of adjustment — spraying the driveway, the fence, or each other rather than the turf.
• Mismatched heads on one zone. Rotors and sprays apply water at completely different rates. On the same zone, one area is always over- or under-watered.
• Blocked or partially blocked nozzles, which narrow the throw.
• Heads that no longer pop up fully, so the spray hits the grass immediately in front of them.
• Pressure problems — too low and the throw falls short; too high and the spray atomises into mist that blows away before it lands.
• Grass grown over heads, which is extremely common and extremely easy to fix.
• Zones that are simply too large for the available flow.

Then set the schedule properly

Once coverage is even, the schedule matters. Deep and infrequent, in the early morning — before sunrise is ideal, because it minimises evaporation and the blades dry as the sun comes up, which reduces fungal pressure.

Evening watering is the worst option in Florida. It leaves the lawn wet through the warm night, which is exactly what fungal disease wants.

Watering must also stay within whatever local restrictions apply, and those change with drought conditions.

Cycle and soak

On compacted soil or a slope, a long run produces runoff — water leaving the property before it soaks in. Splitting the same total time into two or three shorter cycles with gaps between them gets substantially more water into the ground for the same minutes.

Sensors

A working rain sensor is required on Florida irrigation systems and a great many of them have failed without anybody noticing. Check yours actually interrupts a cycle. A soil moisture sensor goes further, watering on need rather than on schedule.