Mistakes after installation: scheduling, commissioning and maintenance

A correctly designed system can still fail after startup

A system designed correctly — pressure measured, zones split properly, pipes sized right — can still perform badly if the mistakes happen afterward, during commissioning, scheduling and maintenance. These mistakes do not show up on the design or while digging: they show up on the water bill, as a patchy lawn, or as cracked pipe after the first frost. For mistakes made at the paper-design stage (spacing, flow, pipe sizing) see Irrigation Design Mistakes: A Pre-Installation Checklist to Avoid Dry Spots and Soggy Zones — this article covers what happens after the system is already in the ground.

Skipping the catch-cup uniformity test at commissioning

A typical commissioning check stops at confirming every head turns and sprays water: if water comes out, the system "works". But a system that sprays water is not the same as one that sprays it evenly. Two adjacent zones with identical scheduling can receive very different amounts of water because of pressure, wind or imperfect head-to-head spacing, and the difference is invisible until the lawn shows a leopard-spot pattern of dry patches after 3–4 weeks.

The catch-cup test (collection cups spread across the zone, measuring volume after a standard run) is the objective check almost no installer runs by default. It costs $15–30 in cups and 20 minutes per zone, and catches poor distribution uniformity before the fix becomes a full reseeding job. The full procedure, with the DU and CU formulas, is at The catch-cup test: check real irrigation uniformity.

Not adjusting arc and radius after startup

Every pop-up nozzle and every rotor has a screw or adjustment ring for the arc (how many degrees it covers) and often for the radius (how far it throws). At first startup, almost no head is already set optimally: arcs spray the driveway or the wall, radii are set to the catalog value instead of the real one for your garden.

Fine adjustment takes 15–20 minutes per zone: run the zone, watch every head, correct the arc with the screwdriver or key supplied, then repeat after a couple of days to confirm the settings hold. Skip this step and you waste water on sidewalks and walls for years — a fix that costs nothing in materials and gets postponed indefinitely.

Skipping anti-drain check valves on sloped zones

On slopes over 5%, when a circuit shuts off, the water left in the pipe drains by gravity to the lowest heads. That creates localized puddling, encourages root rot on the low ground and leaves the high ground drier — a problem with a precise physical cause, not a scheduling one.

The fix at commissioning is to confirm every head on a sloped zone has a built-in anti-drain check valve — a component that costs $1–3 more than the plain version. If you discover the problem after the system is already installed, some check valve models can be added as a separate insert without replacing the whole head.

Ignoring sun exposure in the schedule

A full-sun zone in summer can lose 40–60% more water to evapotranspiration than the same zone facing north or shaded by trees. Running the same duration on every zone is therefore a systematic mistake: sunny zones get too little water, shaded ones too much.

The right schedule splits the garden by exposure and plant type: full-sun lawn, part-shade lawn, shaded shrubs — each zone with its own independent duration and frequency. Smart controllers with ET (evapotranspiration) sensors, like Rachio or Hunter Hydrawise, adjust run time automatically based on the day's temperature and solar radiation. With a basic controller, revise the schedule at least three times a year: spring, peak summer, fall.

No rain sensor installed

An automatic system with no rain sensor keeps irrigating even when the soil is already saturated after a storm. Beyond the wasted water, over-irrigation encourages turf fungal disease, root rot in shrubs and soil compaction.

The rain sensor is the single best cost-to-benefit device in the whole system: it costs $15–30, installs in 30 minutes and wires into the controller's two sensor terminals. Once it registers enough rain (an adjustable threshold, typically 6–12 mm / 0.25–0.5 in), it interrupts the automatic cycle. Choosing between wired and wireless models, and the right threshold for your soil, is covered in Rain sensor for irrigation: legal requirement and how it works.

Forgetting winter drain valves

Without drain valves at the lowest points of the system, residual water in the pipes cannot be fully removed. If it freezes, that water expands and can crack pipes, fittings and sprinkler bodies — damage that only surfaces at spring startup, when it is too late to prevent.

Automatic drain valves open once pressure drops to zero, i.e. when the main valve closes, and cost $2–5 each. If your system does not have them, blowing out the lines with a compressor before winter is the alternative: the full procedure, with the correct pressure and timing to avoid damaging seals, is at How to winterize your irrigation system.

Mixing different precipitation rates on the same zone

This mistake is among the most common in DIY installs and among the hardest to diagnose afterward, because it passes initial commissioning without any obvious problem. Precipitation rate is how many millimeters of water land on the surface per unit of time: a fixed spray head with a 16 ft (5 m) radius typically delivers 1–1.4 in/hour (25–35 mm/h), while a rotor with an MP Rotator nozzle on the same area delivers 0.3–0.5 in/hour (8–12 mm/h). Put both on the same zone, and by the time the spray head has laid down 1.2 in (30 mm) the rotor has only laid down 0.4 in (10 mm).

The result is structurally unfixable by scheduling: the spray zone stays soggy with rot and runoff risk, the rotor zone stays dry. No programming solves this because the precipitation-rate mismatch is a property of the nozzle, not the run time. The only fix is to separate the two nozzle types into distinct zones with separate valves — the choice between nozzle types for each area is covered in How to choose sprinkler nozzles for uniform lawns.

The most common mix I see in residential gardens is 90° sprays in the corners and rotors across the middle of the lawn — a layout that seems to optimize space but creates two hydraulically incompatible zones on one valve. The way to catch this before it becomes a visible problem is the catch-cup test described above, not eyeballing the spray pattern.

Not documenting zones and programs for future maintenance

Two or three years after installation, almost nobody remembers exactly which valve feeds which zone, which nozzle is fitted on which head, or why one program runs a different duration than the others. Without a written map, any maintenance call or future expansion means rediscovering the system from scratch, often by trial and error, opening valve boxes and testing circuits one by one.

The fix takes 30 minutes, once: photograph or sketch the position of every valve with its zone label, note the nozzle model fitted at each head, and record the reason behind any non-standard program duration. The guide to building a map that stays useful for years is at How to map irrigation zones in your garden.