FrostList

When to Winterize Sprinklers in Tempe, AZ

ON TRACK161 days until first 28°F freezeDec 19

Aim to winterize your sprinkler system in Tempe by December 9, roughly a week and a half before the median first 28°F freeze of December 19, which one fall in ten shows up by November 27. The early-to-late range spans roughly 53 days, so treat the median as a midpoint, not a promise.

OUTLOOK

Typical first first 28°F freeze near Dec 19; local deadline about Dec 9. The live 10-day outlook loads here.

Local freeze dates for Tempe

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 18Dec 5Dec 24
28°F (hard freeze)Nov 27Dec 19Jan 19
24°F (severe)Dec 4Dec 31Jan 24

NOAA station: Tempe Asu · 1.1 mi away · 1,167 ft elevation.

The reference station for Tempe is Tempe Asu (1.1 mi, 1,167 ft). First freeze there: 32°F by Dec 5, 28°F by Dec 19, 24°F by Dec 31. That hard freeze has landed anywhere from Nov 27 to Jan 19, a swing of roughly 53 days. Spring's last 32°F freeze clears around Feb 13.

Expect the first frost near Dec 5 in Tempe and the first hard freeze by about Dec 19. The 32°F date swings from Nov 18 at its earliest to Dec 24 at its latest, near 36 days. The last spring freeze averages Feb 13 and as late as Mar 9, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Feb 13, is the one that matters.

Your sprinklers checklist

  1. Shut off the irrigation water supply at the main valve and, if you have one, the dedicated sprinkler shutoff inside the house.
  2. Turn off the controller or set it to the "rain" mode so valves do not open while the system is dry.
  3. Drain the mainline using the manual, automatic, or blow-out method your system was built for; most pros prefer a blow-out.
  4. Connect a compressor to the blow-out port through a proper adapter and run 40–80 psi, one zone at a time, until the heads mist and clear.
    Helpful gear: Air compressor blow-out adapter — Recommended pick
  5. Insulate the backflow preventer and any above-ground valves; this brass assembly is usually the first part to crack.
    Helpful gear: Insulated backflow preventer cover — Recommended pick
  6. Cap outdoor hose bibs with foam covers after the hoses come off so the last exposed fittings stay protected.
    Helpful gear: Foam outdoor faucet covers — Recommended pick
  7. Open the backflow test cocks a quarter turn so any trapped water has room to expand.
  8. Log the date and the psi you used; you will want the reference next fall.

What to have on hand

Air compressor blow-out adapter
Quick-connect fitting that mates a shop compressor to your irrigation line.
Recommended pick
Insulated backflow preventer cover
Pouch that shields the above-ground backflow valve from early frost.
Recommended pick
Foam outdoor faucet covers
Slip-on domes that protect hose bibs after you drain them.
Recommended pick
Portable air compressor
A modest pancake unit moves enough air to clear most home zones.
Recommended pick

What this means locally

Compared with nearby cities, Tempe's first-freeze date near Dec 19 sits close to Scottsdale (Dec 19) and close to Mesa (Dec 19). Arizona's deadlines span Sep 29 to Dec 25 statewide — one date for all of Arizona would be off by weeks for Tempe. Once you know Tempe's freeze date, use it to protect your indoor pipes and winterize an RV if you own one too.

Other winter jobs in Tempe

Every task below is dated to Tempe's own freeze and snow normals.

Frozen pipes → Nov 18Car battery → Dec 19Sump pump → Feb 13RV → Dec 9Boat → Dec 12Motorcycle → Dec 5

See the full Tempe winter checklist, in order →

Frequently asked questions

What temperature freezes sprinkler pipes?
Standing water in shallow lines and the backflow assembly can start to freeze once air temperatures drop into the mid-20s for several hours. Buried mains are slower, but the exposed brass backflow preventer and above-ground valves are the parts that crack first, which is why the deadline is tied to the first 28°F freeze, not the first frost.
Do I need to blow out my sprinklers or just drain them?
It depends on how the system was installed. Manual or automatic drains work if the lines were pitched to low points. Most irrigation pros recommend a compressed-air blow-out because it clears water that drains miss, especially in flat yards. If you are unsure how your system drains, a blow-out is the safer choice.
What happens if I don't winterize my sprinkler system?
Water left in the lines expands as it freezes and can split the backflow preventer, crack valves, or break fittings. Repairs to a backflow assembly commonly run more than the cost of a blow-out. The damage often is not visible until you turn the system on in spring and find leaks.
How much does a sprinkler blowout cost?
A professional blow-out typically costs somewhere in the range of a modest service call, depending on the number of zones and your region. Buying an adapter and using your own compressor costs less over time, but you need enough air volume to clear each zone. Prices rise once the first freeze warnings appear, so book early.
When should I turn my sprinklers back on in Tempe?
Wait until the last spring freeze has passed, which averages around Feb 13 here in the 1991–2020 normals. Turning the system on too early risks refreezing a charged line. Open the main slowly to avoid a pressure surge, then walk each zone to check for winter damage before you rely on the schedule.
Can I winterize sprinklers myself?
Draining and insulating are within reach for most homeowners. A blow-out is doable if you own a compressor that moves enough air and you use a proper adapter, working one zone at a time at safe pressure. If your system lacks a clear blow-out port or you are not confident, hiring a pro once is a reasonable call.

Data: NOAA 1991–2020 normals via Tempe Asu, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.