When someone calls about a stubborn brown patch that will not respond to anything, the first thing we look at is not the grass. It is the sprinkler head nearest to it. A surprising share of lawn problems around Monticello are irrigation problems in disguise, and you can find most of them yourself in about an hour.
Run each zone and watch it
Start the system manually, one zone at a time, in daylight. Almost nobody does this, because systems run before dawn when everyone is asleep. Stand there and watch the whole cycle. You are looking for:
- Heads that do not pop up all the way, or pop up and stay half-risen
- Rotors that have stopped rotating and are just soaking one spot
- Heads spraying the driveway, the road, or the side of the house
- Misting instead of droplets, which means pressure is too high and you are losing water to the air
- Weak, dribbling output, which usually means pressure is too low or the line is partly blocked
- Heads blocked by shrubs that have grown since the system went in
- Wet spots or soggy ground that never dries, which usually means a cracked line or a leaking seal
The catch-can test
This is the single most useful thing you can do. Set straight-sided containers, tuna cans are ideal, across a zone in a rough grid. Run the zone for fifteen minutes. Measure what is in each can.
Two numbers come out of this. First, how long the zone takes to deliver a half inch of water, which is what you need to set a real schedule. Second, how even the coverage is. If the driest can holds half what the wettest one does, you have a distribution problem that no schedule will fix. You will be over-watering part of the zone to keep the rest alive.
Head spacing is usually the culprit
Sprinkler heads are designed for head-to-head coverage, meaning the spray from each head should reach the next head. It looks like overkill and it is not. Anything less and you get dry rings between heads, which is exactly the pattern of most mystery brown spots.
Systems installed cheaply or extended over the years without re-engineering are frequently short on heads. If your catch-can test shows consistent dry gaps in a repeating pattern, that is what you are looking at, and adding a head is a permanent fix where adjusting run times is not.
Do not mix head types in one zone
Spray heads put out water much faster than rotors. If a zone contains both, you cannot set a run time that satisfies either. Whatever you choose, half the zone is over-watered and half is under-watered. This is a common leftover from a system that got extended piecemeal, and the fix is re-zoning or converting heads to match.
Common failures worth knowing
Clogged nozzles. Our sandy soils get into everything. Pull the nozzle, rinse the filter screen, and reinstall. This alone revives a lot of weak heads.
Sunk heads. Over years, soil and thatch build up and the head ends up spraying into the grass rather than over it. Raise it.
Broken risers. Mowers and vehicles snap risers. Sometimes the head still works and just sprays sideways underground, which shows up as a soggy spot plus a dry area downstream.
Failed valves. A valve that does not close fully means a zone that weeps constantly. Look for a permanently wet area near the valve box.
Dead rain sensor. These fail silently and the system just keeps running through storms. Test it by triggering it manually and confirming the next cycle does not start.
Pressure problems
Misting is the sign of too much pressure. It looks like good coverage and it is not, because fine droplets blow away and evaporate before they land. Pressure-regulating heads or a regulator on the zone solves it and usually cuts water use noticeably.
Too little pressure shows up as heads that barely pop, rotors that stall, and coverage that falls short of the design radius. Running too many heads on one zone is the usual cause.
Seasonal settings
A controller set once and left alone will be wrong most of the year. What a lawn needs in a hot dry May is not what it needs in a stormy August or a cool November. At minimum, adjust the schedule four times a year, and shut the system down for the winter dormant period rather than watering grass that is not growing.
Better still, use the seasonal adjust percentage feature most controllers have. Set your peak-summer schedule properly, then dial the percentage down in spring and fall rather than rebuilding the whole program.
When a dry spot is not the irrigation
If coverage checks out and a spot is still struggling, look at compaction, buried construction debris, tree root competition, or a shallow layer of hard fill left from when the house was built. A screwdriver pushed into the soil tells you a lot: if it goes in easily in the healthy area and stops dead in the bad one, you have found your answer.
We keep an eye on head performance and coverage while we are on a property, and we will tell you what we see. Let us know if you want us to walk the system with you.