Is it too late to blow out my sprinklers in Denver, CO?

Past September 24, Denver, CO is into the window where a hard freeze can arrive at any time, so do it 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 Denver, CO?

The long-term normal for the first 32°F freeze in Denver, CO is around October 6, with a normal early year arriving by September 24. A light frost will not usually reach buried pipe — it is a sustained hard freeze, several hours below about 28°F, that does — but an exposed backflow preventer is vulnerable well before that. For calendar context, that median ranks 9th of the 63 metros we publish dates for.

What does it cost to winterize a sprinkler system in Denver, CO?

A professional blow-out in Denver, CO 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.

When can I turn the sprinklers back on in Denver, CO?

The last spring freeze in Denver, CO normally passes around May 6, but that is a median — half of years freeze later than it. Give it a couple of weeks of margin and treat May 18 as the earliest safe date, later if the forecast is still marginal. Re-pressurise slowly, a quarter turn at a time. All told, the system sits out roughly 30 weeks of the year here.

Sprinkler winterization dates

When to Winterize Sprinklers in Denver, CO

Winterizing is a deadline problem, and the deadline is local. In Denver, CO the first freeze of the autumn normally arrives around October 6, which puts the blow-out window at roughly September 8–24 — start about four weeks out and be finished by September 24. Denver, CO's deadline is not the average date, it is the early edge of it: a normal early year freezes by September 24, and the backflow preventer sitting above ground outside your house in Denver, CO is damaged by the first real freeze rather than the tenth.

Winterize between: September 8–24
Average first freeze: October 6; An early year: September 24
Turn it back on after: May 18; Median last freeze May 6, plus a margin — half of years freeze later than the median.

This is the long-term NOAA normal for the nearest first-order station, 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.

That caveat is the ceiling for a static page. YardLedger watches the live forecast for your address instead, and warns you when a hard freeze is actually about to reach Denver, CO. Get my freeze reminder

From the long-term NOAA freeze normals for Denver.

The window against the freeze band

Blow-out window — September 8–24
First-freeze band — from September 24
Median first freeze — October 6

Drawn from Denver, CO's own NOAA freeze normals. The green window ends where the amber band begins: September 24 is the early edge of a normal freeze year, which is the date to be finished by.

Why September 8–24, and not later

A median is not a deadline

Half of Denver, CO's years freeze earlier than October 6, and a normal early year gets there by September 24. Scheduling the work to finish on the average date means missing it every other year.

The backflow device goes first

Buried pipe has soil buying it time. The backflow preventer is brass, above ground and full, so around Denver, CO 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 it out, the few weeks before the first freeze are the busiest of the irrigation year in Denver, CO. 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 dates above are Denver, CO's normals. Your yard's can differ — enter your ZIP for the NOAA station nearest you, rather than the one anchoring Denver, CO. Free, no signup required.

Your ZIP code

Free · no signup · NOAA 1991–2020 normals

How Denver, CO compares

Of the 63 metros we publish winterization dates for, Denver holds the 9th-earliest median first freeze — 8 typically freeze sooner, 54 hold out longer, and Denver lands 19 days ahead of the middle of that list. The closest published dates on either side of Denver belong to Madison, WI (October 5) and Spokane, WA (October 7) — winterization advice written for either transfers here almost unchanged, which is not true of a national average.

Between the median first freeze (October 6) and the median last spring freeze (May 6), Denver's freeze season runs about 212 days — call it 30 weeks with the system down, more than half the year. 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 Denver's median because half of years freeze later still — leaving roughly 153 days of running season between startup and the next blow-out.

Within Colorado, Colorado Springs typically freezes 2 days earlier (October 4). 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 field sequence, numbered as the full winterization guide numbers it — 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

Frequently asked questions

When should I winterize my sprinkler system in Denver, CO?: Between about September 8–24, finishing by September 24. The average first fall freeze in Denver, CO is around October 6, but a normal early year arrives by September 24 — so that early edge, not the average, is the deadline. This is the long-term NOAA normal for the nearest first-order station, 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 Denver, CO?: Past September 24, Denver, CO is into the window where a hard freeze can arrive at any time, so do it 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 Denver, CO?: The long-term normal for the first 32°F freeze in Denver, CO is around October 6, with a normal early year arriving by September 24. A light frost will not usually reach buried pipe — it is a sustained hard freeze, several hours below about 28°F, that does — but an exposed backflow preventer is vulnerable well before that. For calendar context, that median ranks 9th of the 63 metros we publish dates for.
What does it cost to winterize a sprinkler system in Denver, CO?: A professional blow-out in Denver, CO 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.
When can I turn the sprinklers back on in Denver, CO?: The last spring freeze in Denver, CO normally passes around May 6, but that is a median — half of years freeze later than it. Give it a couple of weeks of margin and treat May 18 as the earliest safe date, later if the forecast is still marginal. Re-pressurise slowly, a quarter turn at a time. All told, the system sits out roughly 30 weeks of the year here.