FrostList

When to Winterize Sprinklers in Plymouth, MN

ON TRACK103 days until first 28°F freezeOct 22

Aim to winterize your sprinkler system in Plymouth by October 12, roughly a week and a half before the median first 28°F freeze of October 22, which one fall in ten shows up by October 8. Cold deepens quickly here — only about 10 days separate the first frost from that hard freeze.

OUTLOOK

Typical first first 28°F freeze near Oct 22; local deadline about Oct 12. The live 10-day outlook loads here.

Local freeze dates for Plymouth

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 29Oct 12Oct 25
28°F (hard freeze)Oct 8Oct 22Nov 4
24°F (severe)Oct 19Nov 1Nov 14

NOAA station: New Hope · 3.7 mi away · 910 ft elevation.

Numbers for Plymouth come from New Hope, 3.7 miles away at 910 feet, where the medians fall 32°F by Oct 12, 28°F by Oct 22, 24°F by Nov 1. Year to year the 28°F date has ranged from Oct 8 to Nov 4 — about 27 days apart. Spring's last 32°F freeze clears around Apr 29. Snowfall averages 54 inches a year, first reaching an inch near November.

The freeze arrives in two steps in Plymouth: 32°F around Oct 12, then a hard 28°F near Oct 22. That first freezing night has ranged from Sep 29 to Oct 25, roughly a 26-day spread. On the spring side, the last 32°F freeze clears around Apr 29 and as late as May 12 — the green light for reopening water and de-winterizing. Snow totals near 54 inches a year mean plowing and ice-dam control share the winter to-do list here.

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, Plymouth's first-freeze date near Oct 22 sits later than Maple Grove (Oct 18) and close to St. Louis Park (Oct 22). Minnesota's deadlines span Sep 28 to Oct 19 statewide — one date for all of Minnesota would be off by weeks for Plymouth. Once you know Plymouth's freeze date, use it to protect your indoor pipes and winterize an RV if you own one too.

Other winter jobs in Plymouth

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

Frozen pipes → Sep 29Ice dams → Oct 16Car battery → Oct 22Snow blower → Oct 25Sump pump → Apr 29RV → Oct 12Boat → Oct 15Motorcycle → Oct 12

See the full Plymouth 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 Plymouth?
Wait until the last spring freeze has passed, which averages around Apr 29 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 New Hope, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.