Lawn Care Guides
How to Winterize a Sprinkler System: 80 PSI, or 50
Colorado State puts blow-out pressure at 40 to 80 psi — 80 max for rigid PVC, 50 for polyethylene. And two backflow devices must never see compressed air at all.
In this guide8 sections
Most irrigation systems are not killed by cold. They are killed by water that was still in them.
Illinois Extension’s line is the whole mechanism:
“Water expands as it freezes. It just so happens this expansion is contrary to the rigid nature of our hoses and piping.”
So the job has one goal — get the water out — and two numbers that decide whether the job itself does damage.
The Damage Is Expansion, Not Cold
A buried pipe does not fail because it got cold. It fails because the water inside it turned to ice and needed more room than it had.
That explains where the damage concentrates, and it is not where people look. The buried main is usually deep enough and usually empty enough. What splits is:
- Valves, which hold water in the body by design
- Nozzles and heads, which hold a small volume each and there are dozens of them
- The backflow assembly, which sits above ground in the air temperature
- Any low section the drains never reached, which is the one you cannot see
Which is why “I drained it” and “the water is out” are different claims. A system with drains at the wrong points drains the parts that were never the problem.
The Two Numbers That Decide the Job
Colorado State Extension gives a working range and then two ceilings, and the ceilings are what most guides leave out:
“Ideal pressures are in the range of 40 to 80 pounds per square inch (psi)” — with “80 psi being the maximum for rigid PVC pipe and 50 psi for polyethylene pipe.”
Read that as two different jobs sharing one procedure.
| Pipe material | Maximum blow-out pressure |
|---|---|
| Rigid PVC | 80 psi |
| Polyethylene | 50 psi |
Polyethylene blown at 80 psi is being run at sixty percent over its stated ceiling. The compressor does not know which pipe it is attached to, and neither does the person holding it unless they checked. If you do not know what your lines are made of, 50 psi is the assumption that cannot damage either one.
And one line that reads like boilerplate and is not, because compressed air moves debris out of a nozzle at speed. Colorado State:
“CAUTION! Wear proper eye protection.”
The One Thing That Must Never Be Blown Out
This is the sentence to read before the compressor comes out of the garage. Colorado State, with no hedging in it:
“Pressure Vacuum Breaker (PVB) or Reduced Pressure (RP) backflow prevention devices must never be blown out with compressed air. The rubber seals inside can easily melt from the heat of the air.”
The failure mode is heat, not pressure. Compressed air leaves a compressor hot, and the seals in those two assemblies are the part the whole device depends on. A melted seal does not announce itself in October — it announces itself in April, as a backflow assembly that will not hold pressure and a system that cannot legally be turned on until it does.
So the identification happens first, before anything is connected. If you cannot identify the assembly on your own system, that alone is a reason to have someone who can do the blow-out.
Three Methods, and Which One You Have
Colorado State describes three, and which one applies to you was decided by whoever installed the system:
1. Manual drain valves. Valves at the low points that you open by hand. They “rely on gravity to purge water from the system”, which works only if the pipe was actually pitched toward them.
2. Automatic drain valves. The same gravity principle, opening on their own when pressure drops. Same dependency on the pipe having somewhere to drain to.
3. Compressed air. “Using compressed air to ‘blow’ the water out” — the method for systems without adequate drains, which is most of them.
PlantTalk Colorado’s summary of the risk is worth quoting because it refuses to take a side:
“Poorly handled air pressure can damage a system, as can leaving residual water in the system.”
Both halves are real. Over-pressurised air breaks things now; trapped water breaks things in January. Choosing to skip the blow-out because you have heard air can cause damage is choosing the second failure over the first.
On doing it yourself
PlantTalk states a preference rather than a rule:
“Preferably have the systems blown out by professionals with an air compressor.”
The reason is volume rather than pressure. A consumer compressor usually reaches the psi and not the airflow, so the operator compensates by running each zone longer — which is exactly the condition under which heat and sustained pressure do damage.
The honest division of labour: manual and automatic drains are a homeowner job. Insulating the backflow assembly is a homeowner job. A blow-out on a system you did not install is the part worth paying someone for, and the money buys the identification of your backflow device as much as the air.
Your Deadline Is Your First Frost
PlantTalk is candid that the calendar is the hard part:
“Trying to determine when to shut down irrigation systems becomes quite a challenge.”
Autumn temperatures fluctuate, and the landscape often still wants water when the forecast starts threatening. So the deadline is not a month — it is your own first frost, and a hard freeze can arrive ahead of an average date. The damage happens in one night.
| State | First frost — the outside limit |
|---|---|
| Alabama | Early November (north Alabama) to early December (Gulf Coast) |
| Alaska | Late August in the Interior; September in Southcentral and October in the southern Panhandle |
| Arizona | Occasional light frosts December–January in Phoenix; a few more nights in Tucson |
| Arkansas | Late October (Ozarks) to mid-November (southeast Delta) |
| California | Late November (Sacramento), December (Bay Area); extremely rare in Los Angeles/San Diego |
| Colorado | Mid-September (mountains) to early October (Front Range and Denver) |
| Connecticut | Late September to early October in the northwest hills; late October into early November along the shoreline |
| Delaware | Late October in New Castle County; early to mid-November along the Sussex coast |
| Florida | Mid-December (Panhandle/Tallahassee), January (Orlando/Tampa); frost-free in South FL (Miami) |
| Georgia | Mid-November (Atlanta) to early December (Savannah/coast) |
| Hawaii | no date at all — frost reaches only the high summits of Mauna Kea, Mauna Loa and Haleakala, never the elevations where lawns are kept |
| Idaho | Late August to mid-September in the high mountain valleys; early to mid-October in the Treasure Valley and the lower Clearwater |
| Illinois | Mid-October (Chicago) to late October (southern tip) |
| Indiana | Mid-October (northern Indiana) to late October (Ohio River counties) |
| Iowa | Late September along the Minnesota line to mid-October in the southern counties |
| Kansas | Early to mid-October across most of the state, later in the southeast |
| Kentucky | Mid-October (eastern mountains) to early November (Jackson Purchase) |
| Louisiana | Late November (north Louisiana) to mid-December or frost-free (coastal parishes and New Orleans) |
| Maine | Late August to early September in Aroostook and the western mountains; early to mid-October on the southern coast |
| Maryland | Early October (Garrett County) to early November (lower Eastern Shore) |
| Massachusetts | Late September (Berkshires) to early November (Cape Cod) |
| Michigan | Mid-September (Upper Peninsula), early October (Grand Rapids), late October (Metro Detroit) |
| Minnesota | Early September (northern counties and the Iron Range) to early October (Twin Cities metro) |
| Mississippi | Early November (north Mississippi) to early December (Gulf Coast) |
| Missouri | Mid-October (northern counties) to early November (Bootheel) |
| Montana | Late August to early September at elevation and across the northern plains; mid to late September in the warmer western valleys and the lower Yellowstone |
| Nebraska | Mid-September in the Sandhills and the panhandle; early to mid-October in the south-east |
| Nevada | Mid-September (Great Basin north) to early December (Las Vegas Valley) |
| New Hampshire | Early September in the North Country and the high valleys; mid-October on the Seacoast |
| New Jersey | Mid-October (northwestern Highlands) to early November (shore and Cape May) |
| New Mexico | Early September in the northern mountains; late October into November in the Mesilla Valley and the southern lowlands |
| New York | Late September (Adirondacks), mid-October (Buffalo/Syracuse), early November (New York City and Long Island) |
| North Carolina | Late October (mountains) to mid-November (coast) |
| North Dakota | Early to mid-September across most of the state, earlier in the north-west valleys |
| Ohio | Mid-October statewide |
| Oklahoma | Late October (panhandle) to mid-November (Red River counties) |
| Oregon | Mid-September (high desert) to late November (Willamette Valley and coast) |
| Pennsylvania | Early October (mountains) to late October (Philadelphia) |
| Rhode Island | Early to mid-October in the northwest hill towns; late October to early November on Aquidneck Island and Block Island |
| South Carolina | Late October (Upstate) to late November (coast and the Lowcountry) |
| South Dakota | Mid-September across most of the state, earlier in the Black Hills valleys |
| Tennessee | Late October (plateau) to mid-November (Memphis) |
| Texas | Late November (Dallas/Fort Worth) to mid-December (Houston/Gulf Coast) and rarely (Rio Grande Valley) |
| Utah | Mid-September in the mountain valleys to early November in St. George |
| Vermont | Early September in the Northeast Kingdom and the higher valleys; early October in the Champlain Valley and along the Connecticut River |
| Virginia | Early October (mountains) to early November (Tidewater and Virginia Beach) |
| Washington | Mid-November (Puget Sound lowlands) to early October (Spokane and the northeast) |
| West Virginia | Late September to early October in the Allegheny highlands; late October in the Ohio Valley and the Eastern Panhandle |
| Wisconsin | Early September (northern highlands) to mid-October (Milwaukee and the southeast) |
| Wyoming | Late August to mid-September across most of the state, and hard frost is possible in any month at the higher elevations |
First-frost windows from our own state research, 50 states. Treat the earlier end of a range as the deadline, not the later one.
Watering does not simply stop on that date either — how much the lawn still needs in the weeks before it is a separate question, and how often to water your lawn covers the autumn taper.
If You Barely Freeze
The job gets smaller and does not disappear, because the parts at risk are the ones above ground. Texas A&M AgriLife’s irrigation programme addresses winterization for mild freezing conditions rather than the full northern procedure — the buried lines are not the concern where the ground does not freeze, but the exposed hardware still sits in whatever the air is doing.
PlantTalk’s insulation instruction is the one that applies everywhere:
“Wrap backflow preventers to keep systems operational longer. Use insulation wrapped with plastic and be sure to include pipes to ground level.”
Note the last clause. Insulating the visible brass and stopping at the top of the riser leaves the pipe between there and the soil exposed, which is where it will split.
Illinois Extension adds the fixture most people forget entirely, and it is the cheapest thing on this page: frost-proof spigots, which “usually come standard with an anti-siphon feature that prevents water from siphoning back up from the hose into the home’s water supply.” Disconnect the hose regardless — a hose left attached holds water against the bib and defeats the frost-proof design.
What Spring Actually Costs
The reason this is worth a Saturday is that the repairs are not proportional to the job. A split lateral is a trench. A cracked backflow assembly is a part, a plumber, and in many jurisdictions a re-certification before the system can be used. A dozen cracked nozzles is a morning of finding out which dozen.
And the system does not tell you in October. It tells you the first time you pressurise it in spring, which is also the week you needed it.
The Honest Summary
Get the water out, and do not let the getting-it-out do the damage. Colorado State’s two ceilings are the whole safety margin: 80 psi for rigid PVC, 50 for polyethylene, and the lower number if you are not certain.
Identify the backflow device before anything is connected. PVB and RP assemblies must never see compressed air, because the seals melt rather than the housing breaking.
Drains are a homeowner job; a blow-out on a system you did not install usually is not. PlantTalk’s preference for professionals is about air volume, and the money buys the identification as much as the procedure.
And work to your own first frost, from the table above, treating the early end of the range as the deadline. One night is enough.
Common questions
Frequently Asked Questions
What PSI should I use to blow out a sprinkler system?
Colorado State Extension gives a range and two ceilings, and the ceilings are the part that matters. Ideal pressures are in the range of 40 to 80 pounds per square inch, with 80 psi being the maximum for rigid PVC pipe and 50 psi for polyethylene pipe. So the number depends on what your lines are made of, not on how much pressure your compressor can produce. Poly pipe blown at 80 psi is being run at 60 percent over its stated ceiling. If you do not know which pipe you have, the lower figure is the safe assumption, and a professional will know from the fittings.
Can I blow out my backflow preventer too?
Not if it is one of two common types, and this is the mistake that turns a maintenance job into a repair bill. Colorado State states it without qualification: Pressure Vacuum Breaker (PVB) or Reduced Pressure (RP) backflow prevention devices must never be blown out with compressed air. The reason is thermal rather than mechanical — the rubber seals inside can easily melt from the heat of the air. Compressed air comes out hot, and those seals are the part the device depends on. Identify your backflow assembly before the compressor is connected, not after.
When should I winterize my irrigation system?
Before the first hard freeze, and PlantTalk Colorado is honest that pinning the date is the difficult part: trying to determine when to shut down irrigation systems becomes quite a challenge, because autumn temperatures fluctuate and the landscape may still want water. The practical anchor is your own first frost date rather than a national month — the table further down this page carries the researched first-frost window for each state we cover. Read it as the outside limit rather than the target, because a hard freeze can arrive ahead of an average date and the damage is done in one night.
Do I need to blow the system out, or is draining enough?
It depends on how the system was built. Colorado State describes three approaches: manual drain valves and automatic drain valves, both of which rely on gravity to purge water from the system, and the compressed air method. If your system was installed with drains at every low point and the pipe is pitched to them, gravity does the job. If it was not — and many are not — water sits in the low spots regardless of what the valves do, and that water is what splits a pipe. PlantTalk's framing covers both failure modes in one sentence: poorly handled air pressure can damage a system, as can leaving residual water in the system.
Should I hire someone or do it myself?
PlantTalk Colorado's own preference is stated plainly: preferably have the systems blown out by professionals with an air compressor. That is not a disclaimer. A consumer compressor usually reaches the pressure but not the air volume, so the operator compensates by leaving it running longer on each zone, which is exactly when heat and pressure do damage. The honest split is that manual and automatic drains are a homeowner job, insulating the backflow assembly is a homeowner job, and a compressed-air blow-out on a system you did not install is the one worth paying for.
Why does freezing water break pipes at all?
Because of a physical property Illinois Extension states in one line: water expands as it freezes, and this expansion is contrary to the rigid nature of our hoses and piping. The pipe does not fail from cold — it fails because the ice inside it needs more room than the water did. That is also why the damage concentrates in the parts holding trapped water rather than in the buried main: valves, nozzles, the backflow assembly above ground, and any low section the drains never emptied.
What if I live somewhere that barely freezes?
Then the job is smaller but not zero, and the parts at risk are the ones above ground. Texas A&M AgriLife's irrigation programme addresses winterization for mild freezing conditions rather than the full blow-out procedure a northern system needs. The exposed backflow assembly, above-ground valves and hose bibs still hold water and still sit in the air temperature, so PlantTalk's insulation advice applies even where the buried lines never freeze: wrap backflow preventers, using insulation wrapped with plastic, and be sure to include pipes to ground level.
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📚 Sources & Further Reading
This guide is written against published land-grant university extension research and USDA data. Verify local details with your own state's extension office — and always follow the product label.
- [1]Home Sprinkler Systems: Preparing Your Sprinkler System for Winter — Colorado State University Extension(extension.colostate.edu)
- [2]2205 – Winterizing Sprinkler Systems — PlantTalk Colorado — Colorado State University Extension(planttalk.colostate.edu)
- [3]How to winterize outdoor plumbing - irrigation, hoses, spigots — University of Illinois Extension — Good Growing(extension.illinois.edu)
- [4]Winterization - School of Irrigation — Texas A&M AgriLife Extension Service(irrigation.tamu.edu)
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