Treasure Valley lawn guide
Sprinkler blowout in Boise and Nampa
Water left in sprinkler lines, valves and the backflow preventer expands when it freezes and can crack fittings. A blowout uses compressed air to push that water out before the first hard freeze.
When to schedule it
Most Treasure Valley irrigation districts shut off canal water in mid-October (estimate; dates vary by district each year). Schedule the blowout soon after your water source shuts off and before overnight lows drop into the low 20s°F (estimate).
If you're on city water, you control the timing, but the same freeze risk applies.
Why it matters
- The backflow preventer sits above ground and is usually the first part to crack.
- Cracked lines often aren't found until spring start-up, when they show up as soggy spots or low pressure.
- Repairs typically cost far more than a blowout (estimate).
DIY vs. pro
DIY needs a compressor that moves enough air volume, not just high pressure, and care to keep pressure moderate so you don't damage heads or fittings. Never stand over the backflow while blowing out.
A pro blowout is quick and usually inexpensive in the valley. Seljaas & Sons LLC in Middleton does hands-on irrigation work across the Treasure Valley.
Missed the window?
If a freeze hits first, shut off the supply, open the backflow test cocks and drain valves, and get the blowout done at the next thaw. Drainable parts are the most urgent.
Common questions
Do I need a blowout if I have automatic drain valves?
Auto drains help, but they rarely empty the backflow preventer and low spots completely, so a blowout is still the safest option.
Can I blow out sprinklers myself with a pancake compressor?
Small compressors often can't move enough air to clear a full zone. Blow out one zone at a time, and use a rented tow-behind compressor or a pro for larger systems.
Related LawnWise guides
- Sprinkler Blowout Timing in the Treasure Valley: The Window Is Narrower Than You Think
- Sprinkler Blowout in the Treasure Valley: When It's Due, When You're Late, and What to Do If You Missed It
- Which Backflow Preventer Do You Have? How to Identify It and Drain It for Winter in the Treasure Valley
- Winterizing Your Treasure Valley Lawn: The Complete Fall Checklist
Sources
Figures marked "estimate" are LawnWise rules of thumb for the Treasure Valley, not extension data. Updated 2026-10-30. By LawnWise, from Seljaas & Sons LLC, Middleton, Idaho.