Why sprinklers need to cycle on and off
A sprinkler's precipitation rate is how fast it lays down water, in inches or millimeters per hour. A soil's intake rate is how fast it can absorb that water before the surface saturates. When the precipitation rate is higher than the intake rate, water starts to pool. On a slope, that pooled water runs downhill instead of soaking into the root zone, carrying fertilizer and topsoil with it.
Texas A&M AgriLife Extension notes that as much as 30 to 40 percent of applied irrigation water can be lost to runoff when a system runs longer than the soil can absorb. Cycle and soak breaks one long run into several shorter cycles with a pause, or soak time, between them. The same total amount of water still gets applied; it just arrives in bursts the soil has time to absorb, so little or none of it runs off.
Clay and compacted soils, and slopes of almost any soil type, are the most common candidates. Fast-draining sandy soil on flat ground often doesn't need cycling at all, even with a high-output sprinkler.
| Soil texture | 0–5% slope | 5–8% slope | 8–12% slope |
|---|---|---|---|
| Coarse sandy soil | 1.5–2.0 in/hr | 1.0–1.5 in/hr | 0.75–1.0 in/hr |
| Sandy loam (light sandy) | 0.75–1.0 in/hr | 0.5–0.8 in/hr | 0.4–0.6 in/hr |
| Silt loam or loam | 0.3–0.5 in/hr | 0.25–0.4 in/hr | 0.15–0.3 in/hr |
| Clay loam or clay | 0.15 in/hr | 0.10 in/hr | 0.08 in/hr |
The calculator uses the midpoint of each range above for its soil-and-slope comparison. If you've measured your own infiltration rate, for example with the soil infiltration rate calculator, enter it in the optional field to use that instead.
How this cycle and soak calculator works
The calculator compares your sprinkler's precipitation rate with the maximum rate your soil and slope can typically absorb, then works out the longest single cycle, how many cycles you need, and how long to pause between them.
1. Maximum application rate
Sourced threshold
Maximum rate = midpoint of the published range for your soil texture and slope (or your own measured rate)
See the table above. This is the calculated value the verdict compares your sprinkler's rate against.
2. Maximum minutes per cycle
Cycle length
Minutes per cycle = (Maximum rate ÷ Sprinkler rate) × 60, capped at 60 minutes
This keeps the sprinkler's average output over any hour at or below what the soil can typically absorb. The 60-minute cap applies even when the math allows longer, following Texas A&M AgriLife Extension's advice not to run a zone more than an hour at a time. Minutes are rounded down, never up, so the estimate doesn't overstate how long is safe.
3. Number of cycles and total time
Splitting your total watering time
Cycles = round up (Total watering time ÷ Minutes per cycle)
Total time for the session = Total watering time + (Cycles − 1) × Soak time
Soak time comes from your soil type: Texas A&M AgriLife Extension gives a general range of 30 to 60 minutes between cycles, with at least 60 minutes recommended for clay. This calculator uses 60 minutes for clay loam and clay, and 30 minutes for the lighter textures, since the source doesn't break the range down further by texture.
Unit conversions
Metric precipitation rates convert to inches per hour internally (1 in/hr = 25.4 mm/hr) before comparing against the table, since the source values are published in US units. Minutes and cycle counts don't change with units.
When this calculator isn't the right tool
It splits a run time you already know into cycles; it doesn't calculate that run time for you. Use a different tool for:
- Working out your total watering time first. See the how long to water lawn calculator or the sprinkler run time calculator.
- Measuring your sprinkler's precipitation rate. See the catch-can test calculator.
- Uneven coverage across a zone. A zone with poor distribution uniformity needs longer run times everywhere to reach its driest spots, which changes how many cycles you'll need. See the distribution uniformity calculator.
- Slopes over 12%, or beds and trees on drip irrigation, which apply water far more slowly. See the drip irrigation calculator.
Cycle and soak calculation example
A clay-soil lawn is essentially flat (0–5% slope) and watered with spray heads that a catch-can test measured at 1.5 in/hr. The owner wants 30 minutes of total watering time.
- Maximum rate: clay loam/clay at 0–5% slope is 0.15 in/hr (no range to average; the source gives a single value).
- Minutes per cycle: (0.15 ÷ 1.5) × 60 = 6.0, rounded down to 6 minutes.
- Cycles: 30 ÷ 6 = 5 cycles exactly, so 5 cycles.
- Soak time: clay soil, so 60 minutes between cycles.
- Total time: 30 + (5 − 1) × 60 = 270 minutes (4 hours 30 minutes) from start to finish.
The same calculation in metric
A silt loam lawn on a 5–8% slope is watered with rotors measured at 20 mm/hr. The owner wants 45 minutes of total watering time.
- Convert the rate: 20 mm/hr ÷ 25.4 = 0.7874 in/hr.
- Maximum rate: silt loam at 5–8% slope is 0.25–0.4 in/hr, midpoint 0.325 in/hr.
- Minutes per cycle: (0.325 ÷ 0.7874) × 60 = 24.8, rounded down to 24 minutes.
- Cycles: 45 ÷ 24 = 1.9, rounded up to 2 cycles.
- Soak time: silt loam, so 30 minutes between cycles.
- Total time: 45 + (2 − 1) × 30 = 75 minutes from start to finish.
The clay example needs far more total time than the metric one, even for a shorter watering, because clay's maximum rate is so much lower than a typical spray head's output. That gap is exactly why heavy clay lawns usually do best with rotors or rotary nozzles instead of spray heads.
Measuring your inputs and programming a controller
Identifying your soil type
| Soil type | How it feels |
|---|---|
| Clay | Fine and sticky when wet; a long ribbon forms when rolled. |
| Clay loam | Breaks into hard clods; rolls into a compact mass but not a ribbon. |
| Silt loam | Feels smooth with a moderate amount of fine sand; won't form a ribbon. |
| Sandy loam | Fairly sandy, but enough silt to stay formed with careful handling. |
| Sand | Feels very gritty; forms a cast when squeezed but crumbles when touched. |
If you're still unsure, a local county extension office can identify your soil from a sample or from published soil survey maps.
Measuring your sprinkler's precipitation rate
Set out several straight-sided cans across one zone, run it for 15 minutes, and measure the depth in each can. Average the depths and multiply by four to get inches (or millimeters) per hour. The catch-can test calculator does this math and also flags uneven coverage.
Programming a controller for multiple cycles
Most residential controllers support several start times per zone. To run three 10-minute cycles with a 30-minute soak time, for example: set the zone's run time to 10 minutes, set the first start time, then set the next start time 40 minutes later (10 minutes of watering plus 30 minutes of soak time), and repeat for the third cycle. Many newer smart controllers have a built-in cycle-and-soak setting that does this automatically once you enter the maximum cycle length and soak time.
Check local watering rules first. Some cities restrict total run time or watering hours per zone; where those rules apply, they take priority over a calculated schedule.
What changes the result
The soil-and-slope table above is a starting point. These are the main reasons your real zone might tolerate more or less than the calculated cycle length.
| Factor | Effect | What to adjust |
|---|---|---|
| Soil compaction | Compacted soil absorbs water more slowly than its texture alone suggests. | Aerate before the watering season; use a shorter cycle than the table suggests. |
| Thatch layer | A thick thatch layer can shed water like a shingle roof before it reaches the soil. | Dethatch, or start with a shorter first cycle to test. |
| Existing soil moisture | Already-wet soil has less room to absorb more water before it pools. | Shorten the first cycle of the day and lengthen later ones if needed. |
| Mulch and ground cover | Mulch and dense turf slow surface flow, giving water more time to soak in. | Well-mulched beds can often tolerate longer cycles than bare soil. |
| Sprinkler type | Spray heads apply water much faster than rotors or rotary nozzles. | Switching equipment changes the precipitation rate you enter above. |
| Uneven coverage | Poor distribution uniformity means some areas need longer total run times to catch up. | Check with the distribution uniformity calculator; fix heads before adding cycles. |
If you see standing water or runoff before the calculated cycle ends, shorten it and extend the soak time; if a full cycle finishes with no sign of pooling, you may be able to safely run a little longer than the table suggests.
Frequently asked questions
What is cycle and soak irrigation?
Cycle and soak irrigation splits a zone's watering time into several shorter cycles with a pause in between, instead of running the sprinklers continuously. The pause, called the soak time, lets water already applied move into the soil before more arrives, so the full amount still gets applied without pooling or running off, especially on slow-draining soils and slopes.
How do I know if I need cycle and soak watering?
Compare your sprinkler's precipitation rate with how fast your soil and slope can typically absorb water. If your rate is higher, water will pool and run off before the full watering time is up. This calculator compares the two for you and shows the longest single cycle your soil and slope can typically take before that happens.
How do I find my slope percentage?
Measure the drop in elevation over a set horizontal distance, then divide the drop by the distance and multiply by 100. For example, a 1-foot drop over a 20-foot distance is a 5% slope. Most residential lawns are close to flat and fall in the 0 to 5% range; a slope you can clearly see and feel underfoot is usually 5% or steeper.
How do I find my soil type without a lab test?
Take a handful of moist soil and see how it behaves. Clay feels sticky and can be rolled into a long ribbon. Loam and silt loam feel smoother and hold together loosely without ribboning. Sandy soils feel gritty and fall apart when squeezed. A local county extension office can also help identify your soil from a sample or from soil survey maps.
How long should I wait between cycles?
Extension guidance generally puts the soak time between 30 and 60 minutes, with heavier clay soils needing at least 60 minutes to absorb the previous cycle. Lighter, faster-draining soils can usually use the shorter end of that range.
Does cycle and soak apply to drip irrigation?
Rarely. Drip emitters apply water much more slowly and directly at the root zone, so their effective precipitation rate is usually already well under what the soil can absorb. Cycle and soak mainly matters for sprays, rotors and rotary nozzles, which wet a much larger area much faster.
Can my irrigation controller do cycle and soak automatically?
Many modern controllers have a built-in cycle and soak or multi-cycle feature that splits a zone's run time automatically once you enter a maximum cycle length. Older controllers usually need it set up manually, using multiple start times spaced far enough apart to cover both the cycle and the soak time.
What if my yard's slope is steeper than 12%?
Slopes steeper than about 12% are difficult to irrigate with sprinklers without runoff or erosion, even with cycle and soak. Texas A&M AgriLife Extension recommends drip irrigation for landscapes this steep, or having a professional design the system.
See the drip irrigation calculator.
Who built and checked this calculator
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- Formulas, unit conversions and both worked examples verified by hand.
- Maximum application rates checked against the NRCS/UC Cooperative Extension and Texas A&M AgriLife sources below.
- Soak-time guidance follows Texas A&M AgriLife Extension's published cycle-and-soak recommendations.
Sources
- Swanson, C. & Fipps, G., Texas A&M AgriLife Extension. Preventing Runoff with Cycle and Soak Irrigation (AGEN-PU-218).
- Schwankl, L.J., Prichard, T.L. & Hanson, B.R., UC Cooperative Extension (citing USDA NRCS, 1984). Soil Intake Rates and Application Rates in Sprinkler-Irrigated Orchards (Publication 8216).
- Whiting, D., Colorado State University Extension. Methods to Schedule Home Lawn Irrigation (GardenNotes #265).