When Should You
Open Your Pool?
Open too late and the pool can turn green under the cover. Open too early and a hard freeze can catch refilled pipes. Here's your state's window, from 30 years of NOAA climate data.
The 60°F Rule (and Why 65°F Is Too Late)
Open while your water is still below 60°F, and don't leave it under the cover once it is heading into the mid 60s. Two things change as it warms:
- Algae wakes up. Algae barely grows in cold water and speeds up as the water warms, so every week a covered pool sits above 60°F gives it a head start. Whatever grew over the winter is far easier to clear in cold water than in warm.
- Nothing is fighting back. A covered pool has no pump and no filter running, and whatever chlorine is left from closing is used up faster as the water warms, since warmer water raises chlorine demand (Orenda).
If the popular "open when highs reach 70°F" rule says go, go: in 65 of the 67 cities in our table with an opening deadline, normal highs reach 70°F inside the opening window, a median of 10 days before the water date. Once your window opens, the step-by-step opening guide walks you through the cover, the equipment and the startup chemistry. Opening early is the other half of close late, open early; the fall side is on our closing dates by state page.
Check the Water Under the Cover, Not the Air
A covered pool warms more slowly than the air, because the cover blocks the sun: in a UC Davis study of an uncovered pool, sunlight made up about half of all the heat moving in and out of the water. So measure it: from your open-after date on, lift a corner of the cover once a week at mid-afternoon and check the thermometer and the color. Water near 60°F, or any green tint, means open now, whatever the calendar says.
When to Open Your Pool in Every State
Two dates for the main pool markets in every state. Open after the first, the median last spring freeze, and before the second, when the water usually nears 60°F. The gap between them is your opening window, and the second date is the one that costs money to miss.
Often runs all winter: January averages 47 to 53°F, mild enough that many pools here run all winter with freeze protection on. The dates are for pools that were closed.
Short window: 18 days or less between the two dates, so book early, open by the second date and keep freeze protection on for any late freeze.
Source: NOAA U.S. Climate Normals, 1991-2020. How these dates were worked out
| City | Open aftermedian last freeze | Open beforewater nears 60°F |
|---|---|---|
| Alabama | All states | |
| Birmingham | Mar 21 | Apr 10 |
| MobileOften runs all winter | Mar 3 | Mar 22 |
| Alaska | All states | |
| Anchorage | May 5 | No deadlinewater rarely reaches 60°F |
| Outdoor pools are rare here and almost always heated. Open after the last freeze, around May 5 in Anchorage; unheated water rarely reaches 60°F. | ||
| Arizona | All states | |
| Phoenix | Usually runs all yearFreezes are rare (about 1 winter in 6) | |
| Tucson | Usually runs all yearMedian last freeze Feb 5, 1 year in 10 as late as Mar 2: keep freeze protection on until then | |
| No opening needed: pools here run all year. Spring is the time to raise pump hours back to summer levels and check the salt cell before the heat arrives. | ||
| Arkansas | All states | |
| Little Rock | Mar 21 | Apr 18 |
| California | All states | |
| Los Angeles | Usually runs all yearFreezes are rare | |
| SacramentoOften runs all winter | Feb 2 | Apr 28 |
| Most California pools never close. Central Valley pools that rest over winter can open any time from early February to late April (Sacramento's window runs February 2 to April 28); mountain pools follow a mountain calendar. | ||
| Colorado | All states | |
| Denver | May 5 | May 28 |
| Colorado Springs | May 3 | May 29 |
| Connecticut | All states | |
| Hartford | Apr 21 | May 23 |
| Bridgeport | Apr 5 | May 23 |
| Delaware | All states | |
| Wilmington | Apr 7 | May 11 |
| District of Columbia | All states | |
| Washington | Mar 24 | Apr 27 |
| Florida | All states | |
| Orlando | Usually runs all yearMedian last freeze Jan 25, 1 year in 10 as late as Feb 26: keep freeze protection on until then | |
| TallahasseeOften runs all winterShort window | Mar 11 | Mar 19 |
| Central and South Florida pools run all year. North Florida has the shortest opening window in our table: Tallahassee's median last freeze is March 11 and the water warms about a week later, so open in mid-March and keep freeze protection on through any late freeze. | ||
| Georgia | All states | |
| Atlanta | Mar 15 | Apr 12 |
| SavannahOften runs all winter | Mar 2 | Mar 26 |
| Hawaii | All states | |
| Honolulu | Usually runs all yearFreezes are rare | |
| No opening needed. Pools here run all year. | ||
| Idaho | All states | |
| Boise | Apr 24 | May 23 |
| Illinois | All states | |
| Chicago | Apr 16 | May 21 |
| Springfield | Apr 14 | May 7 |
| Indiana | All states | |
| Indianapolis | Apr 15 | May 11 |
| Iowa | All states | |
| Des Moines | Apr 18 | May 15 |
| Kansas | All states | |
| Wichita | Apr 11 | May 4 |
| Kentucky | All states | |
| Louisville | Mar 31 | Apr 24 |
| Louisiana | All states | |
| New Orleans | Usually runs all yearMedian last freeze Jan 30, 1 year in 10 as late as Feb 27: keep freeze protection on until then | |
| ShreveportOften runs all winter | Mar 9 | Mar 29 |
| Maine | All states | |
| Portland | Apr 26 | Jun 9 |
| Maryland | All states | |
| Baltimore | Apr 10 | May 7 |
| Massachusetts | All states | |
| Boston | Apr 4 | May 29 |
| Worcester | Apr 23 | Jun 5 |
| Michigan | All states | |
| Detroit | Apr 20 | May 21 |
| Grand Rapids | Apr 29 | May 24 |
| Minnesota | All states | |
| Minneapolis | Apr 23 | May 23 |
| Mississippi | All states | |
| JacksonOften runs all winter | Mar 14 | Apr 3 |
| Missouri | All states | |
| St. Louis | Apr 2 | Apr 29 |
| Kansas City | Apr 13 | May 9 |
| Montana | All states | |
| Billings | May 4 | Jun 6 |
| Nebraska | All states | |
| Omaha | Apr 18 | May 12 |
| Nevada | All states | |
| Las VegasOften runs all winter | Jan 20 | Mar 21 |
| Reno | Apr 20 | May 22 |
| Two climates. Las Vegas pools mostly run all winter, and the few that close can reopen from late January to late March, while Reno's window runs from about April 20 to May 22. | ||
| New Hampshire | All states | |
| Concord | May 8 | Jun 3 |
| New Jersey | All states | |
| Newark | Apr 2 | May 12 |
| Atlantic City | Apr 18 | May 17 |
| New Mexico | All states | |
| Albuquerque | Apr 6 | May 5 |
| New York | All states | |
| New York City | Mar 30 | May 12 |
| Albany | Apr 27 | May 24 |
| Upstate's window starts much later than the city's: Albany's median last freeze is April 27, four weeks after New York City's, though its water date (May 24) comes only 12 days later. | ||
| North Carolina | All states | |
| Charlotte | Mar 30 | Apr 19 |
| Wilmington | Mar 19 | Apr 10 |
| Two schedules: the coast first (Wilmington's median last freeze is March 19), then the Piedmont about 11 days later (Charlotte, March 30). | ||
| North Dakota | All states | |
| Fargo | May 10 | May 30 |
| Ohio | All states | |
| Columbus | Apr 18 | May 12 |
| Cleveland | Apr 20 | May 19 |
| Oklahoma | All states | |
| Oklahoma City | Apr 4 | Apr 27 |
| Oregon | All states | |
| Portland | Mar 13 | Jun 1 |
| Pennsylvania | All states | |
| Philadelphia | Apr 2 | May 8 |
| Pittsburgh | Apr 23 | May 19 |
| Rhode Island | All states | |
| Providence | Apr 11 | May 27 |
| South Carolina | All states | |
| ColumbiaShort window | Mar 25 | Apr 8 |
| CharlestonOften runs all winter | Mar 7 | Mar 31 |
| South Dakota | All states | |
| Sioux Falls | May 1 | May 23 |
| Tennessee | All states | |
| Nashville | Mar 31 | Apr 20 |
| Memphis | Mar 16 | Apr 12 |
| Texas | All states | |
| Dallas-Fort Worth | Mar 8 | Mar 30 |
| Houston | Usually runs all yearMedian last freeze Feb 13, 1 year in 10 as late as Mar 12: keep freeze protection on until then | |
| North Texas opens in March: Dallas-Fort Worth's median last freeze is March 8 and the water warms about three weeks later. Houston and South Texas pools mostly run all year; keep a freeze plan until mid-March. | ||
| Utah | All states | |
| Salt Lake City | Apr 8 | May 17 |
| Vermont | All states | |
| Burlington | Apr 29 | May 28 |
| Virginia | All states | |
| Richmond | Apr 3 | Apr 27 |
| Norfolk | Mar 17 | Apr 22 |
| Washington | All states | |
| Seattle | Mar 2 | Jun 16 |
| Spokane | Apr 26 | Jun 16 |
| West Virginia | All states | |
| CharlestonShort window | Apr 16 | May 3 |
| Wisconsin | All states | |
| Milwaukee | Apr 19 | May 30 |
| Madison | May 1 | May 27 |
| Wyoming | All states | |
| Cheyenne | May 12 | Jun 12 |
How these dates were worked out: both come from NOAA's U.S. Climate Normals for 1991-2020, for each city's main weather station. The freeze date is the median last spring night at 32°F, so in half of all years one more freeze comes after it. A light freeze does little harm to an open pool while the pump runs, and the 28°F hard freezes that can crack exposed equipment end a median of 12 days earlier. The water date is when the normal daily average air temperature climbs to 62°F, the same line our closing dates use. A covered pool warms more slowly than the air, so that is about when unheated water nears 60°F. It is an estimate from air temperatures, since NOAA does not measure pool water, and it assumes an unheated pool. Most stations are at airports, and a few sit on the water or downtown (Boston Logan, Central Park), where the last freeze comes early, so inland suburbs can run a week or more later. Outside the US, go by the water rule alone. Your own pool thermometer always beats a table.
Why Opening Early Costs Less
Opening a few weeks early costs some pump electricity and a little chlorine, and cold water uses chlorine slowly. Opening late can cost a green pool cleanup: one 2026 price guide puts green pool cleanup at $200 to $1,500 or more, against $200 to $500 for a routine spring opening (Swimply). If yours does open green, our green pool cleanup guide walks you through it.
Many owners still open late. In a HomeAdvisor poll reported by Pool Magazine, about a third of owners (32.6%) open in June, yet only 8 of the 67 cities in our table with an opening deadline have a water date in June.
Timing Details Most Guides Skip
Your cover type moves the date
A mesh cover lets sunlight and fine debris through (Royal Swimming Pools), and sunlight feeds algae (Loop-Loc), so the water warms and greens sooner: open in the first half of your window. A solid cover blocks the light and buys you more of the window, unless it has torn or held standing water all spring.
Look for freeze damage before you prime
Check the skimmer, the pump and filter housings, the heater and the valves for cracks before you start anything; a cracked part leaks the moment it is under pressure. Inspect your equipment step by step, and if something won't start, try the equipment troubleshooter.
Beat the pollen
In North Carolina, NC State Extension says tree pollen starts as early as February and peaks between late March and early April, right inside the Southeast's opening window. A running pool filters it out; a covered one collects it. Open before the peak if you can, then skim daily and clean the filter more often until it passes.
The early heat-wave trap
A warm week can push the water up ahead of the calendar, faster under a mesh cover. Lift a corner of the cover after any warm spell. If the water is climbing toward 60°F or turning green, open that weekend.
Hiring a Pro? Book in January or February.
Openings bunch up in April and May, and the weeks before Memorial Day are the crunch, when pool companies' calendars fill up fast. Book a month or more ahead of your window and you pick the date. And by our table, Memorial Day is late anyway: in 51 of the 67 cities with an opening deadline, the water date comes by May 25, the earliest date the holiday can fall. Find a local pool pro near you.
Frequently Asked Questions
What water temperature should my pool be when I open it?
Below 60°F is ideal. Open while the water is still cold, and don't leave it under the cover once it is heading into the mid 60s. Leslie's advises opening above-ground pools before the water reaches 65°F. The Open before dates in our table are about when unheated water nears 60°F.
Is it better to open a pool early or late?
Early. A few extra weeks of running the pump in cold water cost little, and cold water uses chlorine slowly. A pool that warms up under its cover, with nothing circulating, can open green. The only real limit is the last freeze, and an open pool with the pump running rides out a light freeze. The shorthand is close late, open early.
Is March too early to open my pool? What about April?
It depends where you live. March is right for North Texas and the Deep South: Dallas-Fort Worth's window runs Mar 8 to Mar 30, and Mobile, Savannah, Charleston SC and Shreveport all have water dates in March. April is opening month around Atlanta (Mar 15 to Apr 12), Nashville (Mar 31 to Apr 20) and Washington (Mar 24 to Apr 27). New York City's window runs Mar 30 to May 12, while Chicago, Detroit and Minneapolis wait for mid to late April. Find your city in the table.
Can I open my pool before the last freeze?
Yes, if you run the pump through every freeze night and keep the equipment's freeze protection on. Moving water rarely freezes, which is why In The Swim and Pentair both advise keeping the pump running through a freeze. The real danger is a hard freeze near 28°F with the pump off or the power out, and in the cities in our table those end a median of 12 days before the last 32°F freeze. If a hard freeze is forecast and your power is unreliable, drain the pump, filter and heater until it passes.
Should I go by air temperature or water temperature?
Water. A covered pool warms more slowly than the air because the cover blocks the sun. The popular "open when highs reach 70°F" rule is still a good cue to start checking: in 65 of the 67 cities in our table with an opening deadline, normal highs reach 70°F inside the opening window, a median of 10 days before the water date.
Is Memorial Day too late to open my pool?
For most of the country, yes. In 51 of the 67 cities in our table with an opening deadline, the water date comes by May 25, the earliest date Memorial Day can fall. The exceptions are much of New England, Colorado, Wisconsin, North Dakota, Montana, Wyoming and the Pacific Northwest. Memorial Day is when you want to swim, so open a few weeks before it.
When should I open a saltwater pool?
On the same dates. Salt cells stop making chlorine in cold water: Hayward's Aqua Rite below 50°F and Pentair's IntelliChlor at 52°F, give or take 3°F, according to their manuals. So an early-opened pool may sit below the cutoff for a while. Reinstall the cell, start the pool on liquid chlorine, and let the cell take over once the panel shows it generating.
When should I open an above-ground pool?
Use the same window. Leslie's advises opening an above-ground pool before the water reaches 65°F. Its hoses and pump sit above ground and freeze faster than buried pipe, so check them for cracks before you start the pump and keep it running through any freeze night after you open.
How far ahead should I book a professional pool opening?
A month or more before your window opens, and January or February is not too early: openings bunch up in April and May. If you'd rather have someone else handle it, find a local pool pro near you.
Know Your Window? Now Open It Right.
The step-by-step opening guide covers the startup sequence, the chemistry order and the freeze-damage checks.
Related: When to Close Your Pool · Green Pool Recovery · Seasonal Supplies Calculator