How to Winterize Your Sprinkler System (Complete Guide)

Why You Need to Winterize Your Sprinkler System

Water expands by about 9% when it freezes. That expansion is enough to crack PVC pipes, shatter sprinkler heads, and destroy backflow preventers from the inside out. A single hard freeze can turn a functioning irrigation system into a collection of expensive problems.

The math is simple. Spending $50 to $100 on winterization (whether you DIY or hire a service) prevents $500 to $2,000+ in spring repair bills. Cracked mainlines require excavation. Broken backflow preventers run $150 to $300 for parts alone. Damaged valve manifolds can take an entire Saturday to replace. Every dollar you spend winterizing your sprinkler system saves you ten in the spring.

Beyond the financial argument, there is the timing problem. When spring arrives and you discover the damage, every irrigation contractor in your area is booked solid. You will wait weeks for repairs while your lawn suffers through the critical early-season growth period without water.

When to Winterize Your Sprinkler System

The trigger is soil temperature, not air temperature. When soil temps drop below 40°F consistently, it is time to winterize your sprinkler system. For most of the country, this means October through November, depending on your USDA hardiness zone.

Northern states (zones 3-5): Early to mid-October. Places like Minnesota, Wisconsin, and Montana can see hard freezes by mid-October.

Transition zone (zones 6-7): Late October to mid-November. The mid-Atlantic, parts of the Midwest, and the Pacific Northwest typically have until early November.

Southern states (zones 8+): Late November to December, if needed at all. Some southern systems only need partial winterization for occasional cold snaps.

Do not wait for the first freeze to remind you. By the time you see frost on your windshield, water in your irrigation lines may have already expanded enough to stress fittings and joints. The best approach: pick a date two weeks before your area’s average first hard freeze and put it on your calendar every year.

How to Winterize Your Sprinkler System: Step-by-Step

Step 1: Shut Off the Water Supply

Locate your irrigation system’s main shut-off valve. This is typically found in the basement, crawl space, or a utility area near where the irrigation line branches off from your home’s water supply. In warmer climates, it may be in a valve box near the water meter.

Turn the valve to the fully closed position. If your system has a bleeder valve or drain cap on the supply side, open it to release any trapped pressure between the shut-off and the backflow preventer.

Step 2: Turn Off the Controller

Set your irrigation controller to “rain mode” or “off.” Rain mode is preferred because it keeps your programmed schedules and settings in memory while preventing any zones from running. This saves you from reprogramming everything in the spring.

If your controller is battery-powered or has a battery backup, leave the batteries in place to preserve your settings. If the controller is in an unheated space that could freeze, consider bringing it indoors for the winter.

Step 3: Choose Your Drainage Method

There are three ways to remove water from your irrigation lines. The compressed air blowout method is the most thorough and the one recommended for most residential systems. We will cover all three in detail in the next section.

Step 4: Blow Out the Lines with Compressed Air

This is the gold standard for winterizing a sprinkler system. Compressed air forces all remaining water out through the sprinkler heads, leaving the lines dry and safe from freeze damage.

Equipment needed: An air compressor capable of delivering 5 to 10 CFM (cubic feet per minute) at 40 to 80 PSI. Most residential systems use polyethylene or PVC pipe, which should never exceed 80 PSI. For systems with PVC pipe, keep pressure at 80 PSI maximum. For polyethylene pipe, stay at 50 PSI maximum.

Process:

1. Connect the compressor to the irrigation system’s blowout port (usually a fitting near the backflow preventer or main shut-off). Use a quick-connect fitting or threaded adapter that matches your system.
2. Close the backflow preventer isolation valves.
3. Start with the zone farthest from the compressor. Open that zone using the controller or manual valve.
4. Gradually introduce air. Do not blast full pressure immediately. Build up slowly.
5. Run air through the zone until no water is visible spraying from the heads. This typically takes 1 to 2 minutes per zone.
6. Move to the next zone. Repeat until every zone has been cleared.
7. Run each zone a second time for 30 seconds to catch any residual water.

Safety note: Never stand over sprinkler heads during a blowout. Debris and water can eject at high velocity. Never look directly into a head while air is flowing. Keep children and pets away from the area.

Step 5: Insulate Above-Ground Components

After blowing out the lines, protect any exposed components from freeze-thaw cycling:

• Backflow preventer: Wrap with insulated covers (foam bags designed for this purpose). Leave test cocks open at a 45-degree angle.
• Exposed pipes: Wrap with foam pipe insulation or heat tape in extreme cold zones.
• Valve boxes: In areas with deep frost lines, fill valve boxes with foam peanuts or insulation bags to prevent direct cold transfer to valves below.

Step 6: Disconnect and Store Removable Components

Any component that can be easily removed should be disconnected and stored in a protected location. This includes hose-end timers, above-ground drip system components, rain sensors mounted on exposed posts, and (critically) your fertigation system tank. More on that below.

The Three Drainage Methods Explained

Manual Drain Method

Systems designed with manual drain valves have drain points installed at the low points of each zone. To use this method:

1. Shut off the water supply.
2. Open all manual drain valves (usually located in valve boxes at the lowest points in the system).
3. Open the drain on the mainline between the shut-off and the backflow preventer.
4. Allow gravity to pull water out of all low points.
5. Open each zone valve (manually or via controller) to release air locks that might trap water in high spots.

Best for: Systems specifically designed with drain valves at every low point. Less effective for flat properties or systems with pipes that run uphill and back down.

Automatic Drain Method

Some systems include automatic drain valves that open whenever line pressure drops below a set threshold (typically 5 to 10 PSI). These valves are installed at low points and drain automatically when the system shuts off.

If your system has auto-drain valves:

1. Shut off the water supply.
2. Run each zone briefly (10 to 15 seconds) to drop line pressure and trigger the drain valves.
3. The valves open and gravity pulls water down and out.

Limitation: Auto-drain valves only clear water below the valve location. Water trapped in heads, risers, and any uphill sections remains. For this reason, many professionals still recommend a compressed air blowout even on auto-drain systems in hard-freeze climates.

Compressed Air Blowout Method

The most thorough approach and the industry standard for winterizing sprinkler systems in freeze-prone areas. Follow the Step 4 instructions above. If you do not own a compressor large enough (5 to 10 CFM minimum), you can rent one from most equipment rental stores for $40 to $75 per day, or hire a professional service.

Winterizing Your EZ-FLO Fertigation System

If you run an EZ-FLO injection system on your irrigation, winterization requires specific steps beyond the standard sprinkler blowout. Skipping these steps risks cracking your tank, corroding fittings, and blocking nozzles when spring arrives.

Pre-Winterization: Flush the Lines

Two to three weeks before your planned winterization date, empty the EZ-FLO tank completely and run 2 to 3 full irrigation cycles with the empty tank still connected. This flushes residual fertilizer solution from every line, head, and fitting in your system.

Why this matters: fertilizer residue left sitting in irrigation lines over winter concentrates as moisture slowly evaporates. The concentrated residue corrodes brass and plastic fittings, crystallizes inside nozzle orifices, and creates blockages that are difficult to clear in the spring. Flushing with plain water before winterization prevents all of these issues.

Disconnect and Store the EZ-FLO Tank

After flushing is complete and you are ready to winterize:

1. Disconnect the tank unit from the irrigation line. The tank itself is not designed to withstand freeze-thaw cycles. Water trapped inside will expand and crack the housing.
2. Drain the tank completely. Invert it and let any remaining water drip out.
3. Clean inline filters. Remove and rinse any filters associated with the EZ-FLO system. Mineral deposits from fertilizer solution build up over a season and restrict flow if not cleaned before storage.
4. Store indoors. A garage, shed, or basement works fine. The key is keeping the unit above freezing temperatures all winter.
5. Inspect O-rings and seals. While the tank is disconnected, check all gaskets and O-rings for wear. Replace any that look cracked or compressed. This takes five minutes now and prevents leaks in the spring.

Spring Reconnection

When you start up your irrigation system in the spring:

1. Reconnect the EZ-FLO tank to your irrigation line.
2. Fill with fresh fertilizer (EZ-FLO Maxx Complete or a seasonal spring blend works well for the first fill).
3. Run one full test cycle before resuming your normal irrigation schedule.
4. Check all fittings and connections for leaks. O-rings that sat dry all winter occasionally need re-seating.
5. Verify flow rate through the system. If any heads seem restricted, the nozzles may need cleaning.

Proper winterization protects your fertigation investment and ensures the system performs at full efficiency from the first day of spring. Neglecting these steps is the number one cause of EZ-FLO service calls in March and April.

Winterizing Your Backflow Preventer

The backflow preventer is often the most expensive single component in a residential irrigation system, and it is the most exposed to freezing temperatures because it sits above ground. Give it proper attention during winterization.

1. Drain both test cocks. Open the small petcocks (usually with a flathead screwdriver) and let any trapped water drain out. Leave them open at a 45-degree angle for the winter.
2. Open the ball valves to a 45-degree angle. This is the half-open position. It prevents water from being trapped between the closed valves while also allowing any condensation to escape.
3. Insulate with a rated cover. Use a foam insulation bag specifically designed for backflow preventers. These are available at irrigation supply stores and rated for specific temperature ranges. Match the rating to your coldest expected temperatures.
4. Schedule your spring backflow test. Many municipalities require annual backflow preventer testing by a certified technician. Schedule your test for early spring so you are compliant and can catch any freeze damage before turning the system back on.

DIY vs. Hiring a Professional

Winterizing your sprinkler system yourself is entirely feasible with the right equipment and a methodical approach.

DIY makes sense when:

• You own (or can rent) an air compressor rated at 5 to 10 CFM
• Your system has 6 or fewer zones
• You are comfortable identifying your shut-off valve, backflow preventer, and blowout port
• You have 1 to 2 hours available

Hiring a professional makes sense when:

• Your system has many zones (7+) or complex routing
• You do not own a compressor and the rental cost approaches the service cost
• Your system includes drip zones, micro-spray, or mixed pressure zones that need careful pressure management
• You want certainty that every zone is fully cleared

Professional blowout services typically cost $50 to $100 for a standard residential system. Many landscaping and irrigation companies offer this as a seasonal service with scheduling convenience. Some offer discounts if you bundle winterization with a spring startup service.

Common Winterization Mistakes

Avoid these errors that lead to expensive spring repairs:

1. Not blowing out every zone. Skipping even one zone leaves water trapped in those lines. Every zone must be cleared individually. Do not assume that blowing out adjacent zones catches everything.

2. Using too much air pressure. Exceeding 80 PSI on PVC or 50 PSI on polyethylene pipe causes cracks, blown fittings, and damaged heads. More pressure does not mean better results. The compressor’s CFM (volume) matters more than PSI.

3. Forgetting the backflow preventer. The backflow preventer holds water in its body and between its check valves. If you blow out the lines but skip the backflow, you will find it cracked in the spring.

4. Leaving the fertigation tank connected. The EZ-FLO tank and any inline fertilizer system must be disconnected and stored indoors. Plastic tanks crack when water inside them freezes and expands.

5. Not insulating exposed pipes. Any above-ground pipe is at risk, even after blowout. Condensation can form and freeze. Wrap exposed sections with foam insulation.

6. Waiting until after the first freeze. By then, damage may already be done. A hard freeze (28°F or below for 4+ hours) is enough to crack pipes with standing water. Winterize before that threshold hits.

7. Running the blowout too briefly. Each zone needs 1 to 2 minutes of airflow, minimum. Short bursts push water around inside the pipe rather than fully expelling it. Keep running until no mist is visible from any head in the zone.

Spring Startup Checklist

When temperatures stabilize above freezing and you are ready to bring your irrigation system back online:

1. Reconnect your EZ-FLO fertigation system. Re-install the tank, check all connections, and fill with fresh fertilizer solution.
2. Close backflow preventer test cocks and valves. Return everything to the normal operating position.
3. Slowly open the main water supply. Turn the valve gradually to let water fill the lines without creating a pressure surge (water hammer) that stresses fittings.
4. Walk each zone while it runs. Look for geysers (broken heads), soggy spots (cracked pipe underground), and reduced flow (blocked nozzles or partially closed valves).
5. Check sprinkler head alignment. Frost heave shifts heads over winter. Adjust any that are spraying sidewalks, driveways, or the wrong direction.
6. Run your fertigation test cycle. Verify fertilizer is flowing through the EZ-FLO system at the expected rate before resuming your full schedule.
7. Resume controller schedule. Adjust run times for spring conditions (typically shorter than summer but more frequent as new growth establishes).
8. Schedule your backflow test. Get it done early before every other homeowner in your area remembers.

Protect Your Irrigation Investment

Winterizing your sprinkler system is one of the highest-return maintenance tasks you can perform as a homeowner. An hour of work in October or November protects thousands of dollars in irrigation infrastructure, ensures your fertigation system is ready to perform on day one of the growing season, and eliminates the frustration of discovering damage when you need your system most.

Mark your calendar, gather your supplies, and make winterization a non-negotiable part of your fall routine. Your lawn, your landscape, and your wallet will thank you in the spring.