Blow out and winterize irrigation before first hard freeze (Oct 1 target for North Idaho)
Irrigation winterization is the single highest-stakes fall task in North Idaho. Water remaining in pipes and valves during a hard freeze (below 20°F) expands and cracks PVC, copper, and polyethylene pipe. The repair bill is always more than the blowout cost.
Post Falls and Coeur d'Alene average first hard frost by October 1–10. Some years it comes in late September. The October 1 target gives a one-week buffer. Do not wait until you "see frost coming" — by then scheduling may be backed up.
Step-by-Step
- 1
Shut off the mainline supply to the irrigation system
Locate the irrigation main shutoff (usually near the backflow preventer or water meter). Close it fully.
- 2
Drain auto-drain systems (if equipped)
Some systems have automatic drain valves at low points. If yours does, open the manual drain, run each zone briefly to relieve pressure, and allow several hours for gravity drainage.
- 3
Air blowout method (most common in North Idaho)
Connect a compressor (minimum 20 CFM — rental unit or professional) to the blow-out access port. Start at the farthest zone from the compressor. Run each zone manually while blowing 40–50 PSI (rotor heads) or 25–35 PSI (spray heads). Never exceed 50 PSI. Run until no water exits heads — usually 3–5 cycles per zone.
- 4
Never stand over or face the heads during blowout
Compressed air blowouts eject water and debris at high velocity. Personal safety: stand to the side and back.
- 5
Drain and insulate the backflow preventer
Open both test cocks on the backflow preventer to drain residual water. Wrap in foam pipe insulation (available at hardware stores). A frozen backflow preventer is one of the most expensive single irrigation failures.
- Homeowner compressors (small tank units, 3–5 CFM) are NOT adequate for irrigation blowouts — they don't provide enough volume to push water out of long lateral lines. You need 20+ CFM.
- Write the blowout date on a sticky note inside your controller panel each year — it's useful when you can't remember if it was done.
- If you have a smart controller, place it in "off" or "rain delay" mode after blowout so accidental zone activation doesn't pressurize a blown-out system.
When to Call LandscapePros
Our irrigation winterization schedule fills up in mid-September for the October target window. Book early — we winterize dozens of properties each fall and availability gets tight. Call us in September to reserve your spot.
Let us handle the whole calendar.
From spring cleanup to winter dormancy — we know what North Idaho landscapes need, season by season.
Blow out and winterize irrigation before first hard freeze (Oct 1 target for North Idaho): Questions We Get Asked
Post Falls and Coeur d'Alene average first hard frost by October 1–10. Some years it comes in late September. The October 1 target gives a one-week buffer. Do not wait until you "see frost coming" — by then scheduling may be backed up.
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