When should I winterize my sprinkler system in Seattle, WA?

Winterize a sprinkler system in Seattle, WA between about October 26 – November 11, finishing by November 11. The average first fall freeze in Seattle, WA is around November 23, and about half of years freeze before it — so the deadline is set a fixed 12 days earlier, a planning buffer rather than a measured early-freeze date. The freeze date above is NOAA's 1991–2020 normal for the station that represents this city, so it describes a typical year rather than this one. Elevation, cold-air drainage and how built-up your street is all move the real date at your address — watch the forecast as the window opens, and act on the first hard freeze in it rather than on the date.

Is it too late to blow out my sprinklers in Seattle, WA?

Past November 11, Seattle, WA is into the window where a hard freeze can arrive at any time, so blow out the sprinklers now rather than waiting for a better weekend — but if a hard freeze has already been through, do not pressurise the system to check it. Drain what you can, leave it off for the winter, and inspect for damage at spring startup instead.

When is the first frost in Seattle, WA?

The long-term normal for the first 32°F freeze in Seattle, WA is around November 23; the planning buffer on this page ends 12 days earlier, at November 11. A light frost will not usually reach buried pipe; whether a colder night does depends on how long it lasts and on how deep and well covered the pipe is, so no single temperature decides it. An exposed backflow preventer is vulnerable well before that. For calendar context, that median ranks 67th of the 68 metros we publish dates for.

What does it cost to winterize a sprinkler system in Seattle, WA?

A professional blow-out in Seattle, WA typically runs $50–250 depending on zone count. Freeze repairs typically run $170–$2,500+, with the backflow preventer the priciest common casualty. If you are doing it yourself, stay at or below 50 PSI and any lower component-manufacturer limit, only where the equipment permits air. If the models, drain paths or air requirements are unknown, use qualified irrigation or backflow service first. This cap does not establish a safe procedure for an unidentified system.

When can I turn the sprinklers back on in Seattle, WA?

The last spring freeze in Seattle, WA normally passes around March 2, but that is a median — half of years freeze later than it. Use March 14 as a planning checkpoint, not a freeze-free date. Check the current forecast and local conditions; postpone startup while freezing remains a concern. Follow the exact installation and backflow model’s filling and air-bleeding instructions; valve sequences differ by model. Use qualified irrigation or backflow service if those instructions are unknown. All told, the system sits out roughly 14 weeks of the year here.

Sprinkler winterization dates

When to Winterize Sprinklers in Seattle, WA

In Seattle, WA the first freeze normally arrives around November 23, which puts the blow-out window at roughly October 26 – November 11 — start about four weeks out and be finished by November 11. Seattle, WA's deadline is a fixed 12-day planning buffer before the average date, because about half of years freeze before it.

The backflow preventer sitting above ground outside your house in Seattle, WA is damaged by the first real freeze rather than the tenth.

Winterize between: October 26 – November 11
Average first freeze: November 23; Planning buffer from: November 11
Spring planning checkpoint: March 14; Median last freeze March 2, plus a margin — half of years freeze later than the median. This is not a freeze-free date; check current conditions.

The freeze date above is NOAA's 1991–2020 normal for the station that represents this city, so it describes a typical year rather than this one. Elevation, cold-air drainage and how built-up your street is all move the real date at your address — watch the forecast as the window opens, and act on the first hard freeze in it rather than on the date.

For Seattle, WA, long-term freeze normals are the ceiling for a static page. YardLedger can alert you to forecast freeze risk when your location, season and notification settings qualify. Forecasts and delivery can change; keep checking local conditions. Get my freeze reminder

From the long-term NOAA freeze normals for Seattle.

The window against the freeze band

Blow-out window and first-freeze band for Seattle, WA. A timeline showing a fixed 12-day planning band, running November 11 to about 12 days past November 23; a blow-out window of October 26 – November 11. the median first freeze at November 23. The window closes at November 11, the early edge of the planning band, not at the median. — Drawn from Seattle, WA's own NOAA freeze normals. The green window ends where the amber band begins: November 11 is the band's early edge and the date to be finished by.

Why October 26 – November 11, and not later

A median is not a deadline

Half of Seattle, WA's years freeze earlier than November 23, so this page sets a 12-day buffer before it. Scheduling the work to finish on the average date means missing it every other year.

The backflow device goes first

Buried irrigation pipe has soil buying it time. The backflow preventer is brass, above ground and full, so around Seattle, WA it can be damaged by the first real freeze rather than the tenth — and it is the most expensive part on the system.

Contractors book out

If you are hiring out sprinkler winterization, the few weeks before the first freeze are the busiest of the irrigation year in Seattle, WA. Booking at the start of the window rather than the end is the difference between a date you chose and one you were given.

When is your first freeze?

The winterization dates on this page are Seattle, WA's normals. Your yard's can differ — enter your ZIP for the NOAA station we match to it, which may not be the one anchoring Seattle, WA. Free, no signup required.

Your ZIP code

Free · no signup · NOAA 1991–2020 normals

How Seattle, WA compares

Of the 68 metros we publish winterization dates for, Seattle holds the 67th-earliest median first freeze — 65 typically freeze sooner, 1 hold out longer, and Seattle lands 27 days behind the middle of that list. Norfolk, VA lands on the very same median as Seattle — a coincidence of climate, not shared data; each metro is measured at its own NOAA station. The closest published dates on either side of Seattle belong to Norfolk, VA (November 23) and Dallas, TX (November 24) — winterization advice written for either transfers here almost unchanged, which is not true of a national average.

Between the median first freeze (November 23) and the median last spring freeze (March 2), Seattle's freeze season runs about 99 days — call it 14 weeks with the system down, under five months — a comparatively short winter. That arithmetic is behind both ends of this page: the blow-out window is the fall edge of it, and the spring-startup date is the other, pushed past Seattle's median because half of years freeze later still — leaving roughly 266 days of running season between startup and the next blow-out.

Within Washington, Spokane typically freezes 42 days earlier (October 12). If your address sits nearer one of those metros, its page is the better anchor. The statewide page, by design, follows the earliest of them rather than the average.

What to do inside that window

The sprinkler winterization field sequence below keeps the step numbers of the full winterization guide — each step opens its full detail there, including which method suits your system.

Professional blow-out

$50–250

If you skip it

$170–$2,500+

DIY pressure ceiling

50 PSI

What it costs, in detail · No compressor? · Draining the backflow preventer

Shutoff questions

When should I winterize my sprinkler system in Seattle, WA?: Winterize a sprinkler system in Seattle, WA between about October 26 – November 11, finishing by November 11. The average first fall freeze in Seattle, WA is around November 23, and about half of years freeze before it — so the deadline is set a fixed 12 days earlier, a planning buffer rather than a measured early-freeze date. The freeze date above is NOAA's 1991–2020 normal for the station that represents this city, so it describes a typical year rather than this one. Elevation, cold-air drainage and how built-up your street is all move the real date at your address — watch the forecast as the window opens, and act on the first hard freeze in it rather than on the date.
Is it too late to blow out my sprinklers in Seattle, WA?: Past November 11, Seattle, WA is into the window where a hard freeze can arrive at any time, so blow out the sprinklers now rather than waiting for a better weekend — but if a hard freeze has already been through, do not pressurise the system to check it. Drain what you can, leave it off for the winter, and inspect for damage at spring startup instead.
When is the first frost in Seattle, WA?: The long-term normal for the first 32°F freeze in Seattle, WA is around November 23; the planning buffer on this page ends 12 days earlier, at November 11. A light frost will not usually reach buried pipe; whether a colder night does depends on how long it lasts and on how deep and well covered the pipe is, so no single temperature decides it. An exposed backflow preventer is vulnerable well before that. For calendar context, that median ranks 67th of the 68 metros we publish dates for.
What does it cost to winterize a sprinkler system in Seattle, WA?: A professional blow-out in Seattle, WA typically runs $50–250 depending on zone count. Freeze repairs typically run $170–$2,500+, with the backflow preventer the priciest common casualty. If you are doing it yourself, stay at or below 50 PSI and any lower component-manufacturer limit, only where the equipment permits air. If the models, drain paths or air requirements are unknown, use qualified irrigation or backflow service first. This cap does not establish a safe procedure for an unidentified system.
When can I turn the sprinklers back on in Seattle, WA?: The last spring freeze in Seattle, WA normally passes around March 2, but that is a median — half of years freeze later than it. Use March 14 as a planning checkpoint, not a freeze-free date. Check the current forecast and local conditions; postpone startup while freezing remains a concern. Follow the exact installation and backflow model’s filling and air-bleeding instructions; valve sequences differ by model. Use qualified irrigation or backflow service if those instructions are unknown. All told, the system sits out roughly 14 weeks of the year here.