Irrigation controller programming and scheduling field guide

What good scheduling does, and where most controllers fail

Good controller programming puts the right depth of water on the root zone at the right interval, then gets out of the way. The job is three numbers per zone: how long it runs, how often, and what time it starts. Set those from the plant's need and how fast the zone applies water, and the landscape stays healthy on the least water it can. Set them by feel and the controller overwaters, every cycle, for years.

The default failure in this trade is set-and-forget. A system gets programmed once at install, usually to the wettest setting so nothing browns out on the walk-through, and nobody touches it again. The seasonal adjust never moves, the run times never get checked against a precipitation rate, and the property pays a July water bill in October. Most controllers in the field are not broken. They are running a schedule nobody built on purpose.

The controller does not know your soil, your slope, or your plants unless you tell it. A timer runs the clock you give it whether that clock floods the bed or starves it. A smart controller can compute a schedule, but only from the zone information you enter and the precipitation rate the heads actually apply. Either way the schedule is a decision. This guide is how you make it on purpose instead of by habit.

What is a smart irrigation controller?

A smart irrigation controller adjusts watering automatically to the weather or the soil instead of running a fixed clock, and EPA WaterSense labels two kinds: weather-based and soil-moisture-based. A conventional controller is the third kind, the plain timer that does exactly what you program and nothing more. The difference between them is who decides when to water.

A conventional, clock-based controller runs the days, start times, and run times you set, with a seasonal adjust percentage you move by hand. It is fine hardware. The problem is the hand, because the hand rarely moves, so the July schedule runs all year.

A weather-based, or ET, controller pulls local evapotranspiration and weather data and recomputes the run time as demand changes, watering more in a hot, dry week and less after rain. It estimates the water the plants lost and replaces it. A soil-moisture controller comes at the same goal from the other end: a buried sensor reads how wet the root zone is and lets a cycle run or skips it. WaterSense labels both, and either one saves water mostly by skipping the water the plants did not need.

Central or cloud control is the commercial tier. One account runs many controllers across many sites from a phone or a desktop, feeds ET to each site, and pushes back flow alarms and faults. It is covered later under commercial sites. The point that holds across all of them: the controller type decides who adjusts the schedule, but none of them fixes a zone that applies water unevenly.

Zones, stations, and hydrozones

A zone, or station, is one valve and the group of heads it runs, and the rule that makes scheduling possible is one zone per hydrozone. A hydrozone is a group of plants that share the same water need, the same sun, and the same application rate. Turf in full sun is one hydrozone. A shaded shrub bed is another. They do not belong on the same valve, because no single run time serves both.

Every head on a zone should be the same type at a matched precipitation rate. Spray with spray, rotor with rotor, drip with drip. Mix a spray and a rotor on one valve and the spray lays down water three to four times faster, so the spray area floods while the rotor area stays dry, and no run time fixes it. That matched-precipitation rule and how an audit catches a violation are covered in the irrigation audit guide.

Never put drip and spray on the same zone. They run at different pressures and wildly different rates, drip in gallons per hour over an hour or more, spray in gallons per minute over a few minutes. One of them is always wrong on a shared valve. Beds go on drip zones, turf on spray or rotor zones, each on its own valve and its own program. The drip design and why the two cannot share a valve are covered in the drip irrigation guide.

When a zone mixes hydrozones, the symptom is the same every time: half the zone is right and half is wrong, and you cannot schedule your way out of it. The fix is at the valves and the pipe, not the controller.

Watering depth and the plant's need

The depth you apply should refill the root zone to the depth the plant needs, no deeper. Water that soaks below the roots is gone, past where the plant can reach it, and it carries fertilizer down with it. The plant need comes from evapotranspiration, the water lost from the soil and the plant together, and you scale a published reference figure to your plants.

Reference ET, written ETo, is the demand for a standard surface under the day's weather, published by many water authorities and weather networks. Your plant need, ETc, is ETo times a crop coefficient, Kc, that differs for turf, shrubs, and trees. That is part of why those plants belong on separate zones: they lose water at different rates and want different depths. The audit guide covers ET, ETo, and the crop coefficient in more depth.

Root depth sets how much water a single cycle should deliver. Turf roots run a few inches deep, shrubs deeper, trees deepest, and the goal of a cycle is to wet the whole root zone and then let it dry before the next one. A shallow sip every day wets the top inch and trains roots to stay there, shallow and weak. A deeper soak less often pulls roots down where the soil holds more water and the heat does less damage. The depth and the interval are one decision, made together.

ETo

Reference evapotranspiration, the water demand of a standard surface under the day's weather

Kc

Crop coefficient, the factor that scales ETo to a specific plant type's need

Root zone

The depth of soil the plant's active roots occupy, which a cycle should wet and then let dry

How long should you run each zone?

Run time for a zone is the depth you want to apply divided by how fast the zone applies water, its precipitation rate. In plain numbers, run time in minutes equals the net depth needed in inches times 60, divided by the precipitation rate in inches per hour. A zone that needs 0.5 inch and applies 1.5 inches per hour runs 20 minutes. Change either number and the run time moves with it.

The precipitation rate is the input people guess and get wrong. It is the inches per hour the heads actually lay down at the real operating pressure, measured with a catch-can test or calculated from the flow and the area. The irrigation audit guide covers measuring it both ways, including the 96.25 formula and the catch-can method, and it carries the uniformity-adjusted run time that stretches the clock to cover the dry quarter of an uneven zone. Use that fuller version once you have audited the zone.

A spray zone near 1.5 to 2.0 inches per hour reaches a useful depth in minutes. A rotor near 0.4 to 0.6 inches per hour needs three to four times longer for the same depth, which is the whole reason sprays and rotors cannot share a valve. Drip, slower still, runs for an hour or more. The run time always tracks the rate, so the first question on any zone is how fast it applies water, not how long it has always run.

PR

Precipitation rate, the depth a zone applies per hour in inches per hour, measured or calculated

Net depth

The depth the plants need for the period after subtracting effective rainfall

What is cycle and soak?

Cycle and soak splits a zone's run time into several shorter cycles with a soak break between them, so the water soaks in instead of running off. The controller waters a few minutes, moves to other zones while that one soaks, comes back for the next cycle, and repeats until the total run time is delivered. Same water on the plants, none of it in the gutter.

It is the fix for runoff, and runoff happens when the precipitation rate beats the soil's intake rate. A spray near 2 inches per hour overruns most soils within a few minutes. Clay is the hard case, with an intake rate well under a tenth of an inch per hour, so it ponds almost at once. Add a slope and the water sheets off sooner, because gravity carries it away before it can soak in.

Clay and slopes want shorter cycles and longer soaks; sandy, flat ground often takes its whole run time in one cycle. A common pattern on a clay slope is to break an 18-minute run into three 6-minute cycles with 30 minutes or more of soak between them, while the controller runs other zones in the gap. The numbers vary with the soil, so the field test is simple. If you see water tracking down the sidewalk during a cycle, the cycle is too long for that soil. Cut the cycle and add a soak. The audit guide ties cycle and soak to the measured precipitation rate and the soil intake.

Watering frequency: deep and infrequent, and the establishment taper

Watering frequency follows the soil and the roots, not the calendar. Deep and infrequent is the default for established plants: a cycle that wets the whole root zone, spaced days apart, so the soil dries between waterings and the roots chase the water down. Shallow and frequent does the opposite, keeping the surface wet, the roots shallow, and the plant dependent on the next sip. The depth per cycle comes from the plant need; the interval comes from how fast the soil and plant use that depth.

Soil sets how much water the root zone holds and therefore how long it lasts between cycles. Sandy soil holds little, dries fast, and wants more frequent, smaller cycles. Clay holds more and stretches the interval, as long as cycle and soak gets the water in without runoff. Loam sits between. The mistake is running every zone on the same days regardless of what each one is planted in.

New plantings break the deep-and-infrequent rule on purpose, then return to it. Fresh sod and new plants have roots only in the top inch or two, so they need frequent, light watering to keep that shallow zone from drying while the roots establish. Then you taper. Stretch the interval and deepen the cycle over the following weeks as the roots go down, until the plant is on the mature deep-and-infrequent schedule. Run new sod on the mature schedule and it dries out before it roots. Run a mature lawn on the establishment schedule and you grow a shallow-rooted lawn that wilts the first hot week. The establishment schedule for sod and new plantings is its own topic, but the controller side is the taper from frequent-and-shallow to infrequent-and-deep.

Seasonal adjust and the water budget

Seasonal adjust, also called the water budget or percent adjust, scales every run time in the controller up or down by a percentage without reprogramming each zone. Set the peak-summer run times from the precipitation rate and plant need, call that 100 percent, then ride the percentage down through spring, fall, and the shoulder months as demand drops. If a summer zone runs 20 minutes, a 50 percent setting runs it 10.

The reason it matters is that plant need is not constant. Evapotranspiration in July can be double what it is in April or October, so a fixed schedule that suits July throws roughly half its water away in the shoulder seasons. Seasonal adjust is the one knob that tracks that change on a basic controller, and it is the knob nobody turns. A system left at 100 percent all year is the most common overwatering pattern in the trade.

Better controllers let you preset a percentage for each month, so the controller steps itself down and back up through the year without a trip to the box. Best, a weather-based controller pulls local ET and adjusts daily, which is seasonal adjust done automatically and continuously instead of in monthly steps. Whichever you have, the move is the same: program the peak schedule once from real numbers, then let the percentage carry it through the seasons. Set it and ride it. Do not set it and forget it.

Setting up a smart, weather-based controller

A weather-based controller earns its label only if you set up each zone correctly, because it computes the schedule from the zone information you enter plus the local weather it pulls. Garbage in, garbage out. The controller asks for the things that change how much and how often a zone needs water, and it needs an honest answer for each.

The per-zone inputs are the plant type, the soil type, the sun exposure, the slope, the head or emitter type, and the precipitation rate. Plant type and sun set the demand. Soil and slope set how fast water can go in before it runs off, which drives the cycle and soak the controller builds. The precipitation rate is the one input that has to come from the system itself, measured or calculated, not guessed, because it converts the computed depth into a run time. Enter a wrong precipitation rate and a smart controller computes a wrong schedule with full confidence.

With those entered, the controller pulls local ET, computes the depth each zone needs, divides by its precipitation rate for a run time, splits that into cycles for the soil and slope, and sets the interval from the demand. EPA WaterSense labels weather-based and soil-moisture controllers that meet its efficiency criteria, and many water authorities point rebates at the labeled models. The label is on the box. The savings are in the setup, so do not skip the zone-by-zone entry to save twenty minutes at install.

Rain, freeze, and soil-moisture sensors

Sensors override the schedule when watering would be wasted or harmful, and the rain sensor is the one most often required by law. A rain shutoff senses rainfall and suspends the cycle so the system does not run during or right after a storm. Florida requires a rain sensor or equivalent shutoff on automatic irrigation systems under state law, and California requires a rain shutoff or real-time weather adjustment on new systems. Other jurisdictions vary, so confirm the local requirement before you call a system compliant.

A freeze sensor suspends watering below a set temperature, because irrigating into a freeze coats the plants and the pavement in ice, which is both a plant-damage and a slip hazard. In cold climates it is cheap insurance against the controller running its normal early-morning cycle into a hard frost.

A soil-moisture sensor reads the water in the root zone and either runs a controller of its own or vetoes a scheduled cycle when the soil is already wet. It is the most direct measure of plant need there is, because it reads the soil instead of estimating from weather, but it has to sit in a representative spot at root depth and get checked, since a sensor in the wrong place lies. Whatever sensors you install, wire them in and test that they actually interrupt a cycle. A rain sensor that was never connected, or was bypassed at the controller and never switched back, is the quiet reason a system runs through a downpour.

Flow sensing and the master valve

A flow sensor measures how much water the system is moving and catches a break the schedule never would. It reads the flow on each zone, learns the normal range, and flags a reading that runs high, a stuck valve, a broken lateral, a sheared head, or low, a clogged zone or a closed valve. Paired with a master valve, the controller can shut the water off when the flow goes wrong instead of running a mainline break for hours.

The master valve is a valve at the source that the controller opens only while a zone is calling for water, so the mainline downstream is dead the rest of the time. On its own it limits how long a break can run. With a flow sensor watching, it becomes automatic: the sensor sees the unusually high flow of a mainline break, the controller closes the master valve, and it sends an alert instead of flooding the site until someone notices the water bill or the washout.

This is mostly a commercial feature, and on larger systems it pays for itself the first time it catches a break overnight. California now requires flow sensors and a master valve on new commercial irrigation systems, part of the same efficiency push behind weather-based control, while residential rules are lighter. The value is the same everywhere. A flow sensor turns a break from a flood you find on the next visit into an alert you get the night it happens.

Programs A, B, and C and the start times

A program is a set of zones, days, and a start time that run as a group, and most controllers carry several, named A, B, and C or program 1, 2, and 3. Use them to separate zones that water on different schedules. Drip beds want a long, infrequent program. Turf sprays want a shorter, more frequent one. A slope on cycle and soak may want its own start time so its cycles do not collide with everything else. Grouping unlike zones into one program forces them onto one schedule, which is the same mistake as mixing hydrozones on a valve, one level up.

Zones inside a program run in sequence, not at once, because the supply cannot feed them all together. So the program start time is when the first zone fires, and the rest follow as each finishes. Cycle and soak uses the gaps between a zone's cycles to run other zones, which is why the soak time is free instead of dead air.

Start in the early morning, commonly the few hours before sunrise. The wind is calm, so spray lands where you aimed it. Pressure is up, because demand on the main is low. And the foliage dries as the sun comes up, which midday and night watering both get wrong. Midday loses water to evaporation and wind and can scorch wet leaves in the sun. Night watering leaves the foliage wet for hours, which invites fungus and disease. The early-morning window is not a preference. It is the one time that fixes three problems at once.

Scheduling the drip zones

Drip zones run long and infrequent, the opposite of spray, and they belong on their own program. Because drip applies water slowly, in gallons per hour at the root, a drip zone often runs 30 to 90 minutes or more and waters every few days rather than daily, so the water soaks deep and the soil dries between cycles. Leave a drip retrofit on the old spray schedule, short and daily, and you keep only the surface wet and the roots shallow, which is the most common drip scheduling mistake there is.

Set the drip run time from the zone's application rate or the gallons each plant needs, not from a spray clock. The drip irrigation guide covers converting emitter output to an effective precipitation rate and building the run time from plant demand, along with why drip and spray cannot share a valve or a program. Group all the drip zones into one program with the long, multi-day schedule, and keep the turf spray on a separate program with its shorter, more frequent runs. One controller runs both as long as they are on separate programs and valves.

Drip wants the same sensors as everything else. A drip zone that runs through a rainstorm is exactly the waste a restriction cites, and a rain or soil-moisture sensor is a cheap add that stops it.

Watering windows and local restrictions

Watering windows and day restrictions come from the local water authority, and they override your ideal schedule. Many jurisdictions cap which days you can water, often by address, odd or even, and which hours, usually barring midday to cut evaporation. Some set a hard window, some a seasonal limit, some tighten further under drought. Program to the allowed days and hours first, then fit the run time and frequency the plants need inside that window.

The conflict is real when the window is tight. If a property is allowed two days a week but the plants want three lighter waterings, you consolidate into deeper cycles on the allowed days, leaning on cycle and soak so the deeper application still soaks in instead of running off. A long single run on a restricted day is exactly where runoff shows up, so the restriction and cycle and soak get programmed together.

Drip is often the way out. Many restrictions exempt or relax the days for drip and low-volume systems, because they do not throw water on hardscape and do not run off, so a bed on drip can water when a spray zone cannot. Confirm the local rules before you build the schedule, because watering on a barred day is how a property gets cited, and the controller is the thing that did it on the owner's behalf.

The schedule is only as good as the system

The schedule is only as good as the system it runs. A perfect run time on a zone with broken heads, mismatched nozzles, or low pressure still leaves dry spots, and the operator's reflex is to add minutes until the worst spot greens up, which floods everything else. You cannot schedule your way out of a coverage problem. You fix the coverage, then you schedule.

So the order is audit first, program second. Walk the zone running, fix the tilted and sunken and clogged heads, set the pressure, confirm matched precipitation, then measure the precipitation rate and the distribution uniformity and build the schedule from those numbers. The irrigation audit guide covers the catch-can method, the uniformity math, and the run time that accounts for an uneven zone. Program a freshly audited system and the run times mean something. Program over a broken one and you are just choosing how much to overwater.

This is the step that turns a schedule from a guess into a number you can defend. The audit gives you the precipitation rate the run time formula needs and the uniformity the dry quarter needs. Without them the controller is set by feel, and feel always overwaters.

Central and cloud control for commercial sites

Central or cloud control manages many controllers across many sites from one account, and it is how commercial and municipal irrigation runs now. Instead of driving to each clock, a manager pulls up every site on a phone or a desktop, pushes a schedule change to a hundred controllers at once, and receives faults and flow alarms as they happen. The ET feed goes out to each site by its own local weather, so a schedule adjusts per site, not per system.

The payoff on a large portfolio is the alerting. A flow sensor at each site reports a break or a high-flow event to the central platform, which can shut the affected controller's master valve and notify the crew, so a mainline break at a remote site becomes a middle-of-the-night alert instead of a washout found on the next visit. Stuck valves, no-flow zones, and sensor faults surface the same way, by exception, so the manager works the problems instead of inspecting every site blind.

The schedule logic underneath is the same as a single smart controller: per-zone setup, ET-driven run times, cycle and soak, seasonal tracking. Central control does not change the irrigation. It changes how many systems one person can keep honest and how fast a failure gets caught. Record which controller serves which zones and which account they live under, because on a multi-site system the map is the only thing that makes a late-night alert actionable.

Controller maintenance and seasonal shutdown

A controller schedule drifts out of true if nobody maintains it, and the maintenance is short but real. The backup battery or the controller's clock can lose the date and time after a long power outage, and a controller running the wrong day waters on a barred day or skips the program entirely, so check that the date, time, and programs survived any outage. Replace the backup battery on the schedule the manufacturer gives, before it dies, not after.

Sensors need a check too. A rain sensor's element wears and can stick, a soil-moisture sensor can foul or shift, and a flow sensor can drift, so test that each one still interrupts a cycle the way it should. A sensor that quietly stopped working is a schedule running with no safety net. Re-program the seasonal adjust at the season changes, or confirm the weather-based controller is still pulling its ET feed, because a smart controller that lost its data connection has quietly reverted to a fixed fallback schedule.

Seasonal shutdown is its own task in freezing climates. Before the first hard freeze the system gets winterized, draining or blowing out the lines so water left in the pipes, valves, and backflow does not freeze and crack them, and the controller is set to its off or rain mode for the winter. Winterization is a topic of its own, and drip changes how you blow out, which the drip irrigation guide covers. In spring the system gets charged back up and the schedule re-set for the new season. Put the re-program on the calendar at both ends, because a system that comes back on in spring running last fall's settings overwaters until someone notices.

What to document

A schedule nobody wrote down is a schedule the next tech reverse-engineers from the box and a hose. Record the program for each zone so the schedule can be defended, adjusted by season, and rebuilt after a controller swap or a power loss wipes it. Capture the plant or hydrozone, the precipitation rate, the depth applied, the run time, the cycle and soak split, and the watering days, per zone, not per system.

The table below is the per-zone line. Fill one for every zone, because the whole point of programming is that zones differ. Note the controller model and the program letter too, so the record maps to the hardware, and write down the seasonal adjust setting and whether the controller is weather-based, so the next person knows whether the run times are the peak schedule or a scaled one.

Common mistakes

• Setting the schedule once at install and never adjusting it, so the peak summer clock runs all year.
• Leaving the seasonal adjust at 100 percent through spring and fall instead of riding it down with demand.
• Running long single cycles on clay or slopes and sending the water to the curb instead of using cycle and soak.
• Mixing drip and spray, or unlike hydrozones, on one zone or one program, so no run time serves all of it.
• Watering midday, where evaporation and wind steal it, or at night, where wet foliage invites disease.
• Building the run time from habit instead of the zone's measured precipitation rate and the plant's need.
• Leaving the rain or soil-moisture sensor disconnected or bypassed, so the system runs through rain.
• Entering a guessed precipitation rate into a smart controller, which then computes a wrong schedule with confidence.
• Running new sod or plantings on the mature deep-and-infrequent schedule before the roots establish.

Field checklist

Standards and references

The Irrigation Association sets the scheduling best practice this guide follows, including the precipitation-rate and run-time math and the audit method behind a defensible schedule. When you name a method on a report, name the IA procedure, because that is what utilities recognize.

EPA WaterSense runs the federal efficiency program, labeling weather-based and soil-moisture controllers and pressure-regulating spray bodies that meet its criteria and certifying irrigation professionals through approved programs. It is the label rebates point at, so a WaterSense-labeled controller is often what qualifies a system for a utility program. The landscape irrigation standard developed under ASABE and adopted through ICC, commonly cited as ICC 802, covers sprinkler and emitter system efficiency and uniformity. Reference it by topic and confirm the current edition rather than citing a section from memory.

Above all of it sits the local water authority. The watering days and hours, the rain-sensor and shutoff requirements, the flow-sensor and master-valve rules on new commercial systems, the drought restrictions, and the rebate eligibility are set by the jurisdiction and the state, and they vary and they change. Florida requires a rain sensor by statute, and California requires weather-based adjustment, a rain shutoff, and on new commercial systems flow sensing and a master valve. Confirm the adopted code, the local amendments, and the authority's current rules before you build to any number here, and let those rules override any general target. The equipment manufacturer's data governs the controller's own setup and limits.

Units and terms

Scheduling numbers cross between depths, rates, and percentages, and the same idea reads differently on a controller face, a nozzle chart, and a utility form. Keep the depth, the rate, and the time straight and the schedule math stays honest.

Run time is minutes per cycle. Depth and plant need are inches, the same units as rainfall, so a 0.5 inch application against a 0.5 inch daily ET is directly comparable. Precipitation rate is inches per hour. Frequency is days between waterings, or waterings per week. Seasonal adjust and distribution uniformity are dimensionless, read as a percent or a fraction. Flow is gallons per minute for spray and rotor zones, and gallons per hour per emitter for drip.

Hydrozone

A group of plants sharing water need, sun, and application rate, scheduled together as one zone

ET / ETo / ETc

Evapotranspiration: reference demand ETo scaled by a crop coefficient to the plant need ETc

Precipitation rate (PR)

The depth a zone applies per hour, in inches per hour, the divisor in the run-time formula

Cycle and soak

Splitting a run into shorter cycles with soak breaks so water infiltrates instead of running off

Seasonal adjust / water budget

A controller percentage that scales every run time up or down as plant demand changes through the year

Station / program

A station is one valve and its heads; a program is the zones, days, and start time that run as a group

Master valve

A source valve the controller opens only while a zone runs, limiting how long a break can flow

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