Frost Dates
I've had quite a few questions regarding last frost dates. The last
frost date for an area is the last day in the spring that you could have
a frost. The average last frost day is the date on which in half of
the previous years the last frost had already occurred (so about half of
the time it will not frost again and it will be safe to plant tender plants).
Most planting directions are based on the average last frost date.
The calendar based directions I give (Now it is time to... etc.)
are usually based on an average last frost date of April 1st.
An important thing to realize about last frost dates is that the actual date
of the last frost is different every year. It can be much earlier than
the average or much later. This is especially important for tender
plants that can be killed by a frost. For hardier plants, the average
last frost date is more an indicator of general growing conditions than a
danger sign.
After hours of searching on the internet, I've been unable to find a definitive
list of average last frost dates for the entire US. There are, however
many sites with local information or more general information. Below
I've listed some of the more useful sites. (Please let me know if you
know of other useful sites.)
If the sites below do not have information that is specific enough for your
location, contact your local Cooperative Extension
Agent. They should have the best local data on average last frost
dates.
Remember, Micro-climates play an important role in frost dates. Features
like hills or water can significantly affect temperatures. Thus, neighbors
might have somewhat different average last frost dates.
Frost Sites
Old
Farmer's Almanac US Last frost chart - A chart listing the average last
frost date for key cities in every state in the US.
Old
Farmer's Almanac Canada Last frost chart - A chart listing the average
last frost date for key cities in every Province in Canada.
NOAA Frost Maps - Maps showing length of growing season,
last spring freeze and first fall freeze. Choose the high resolution
maps to see your local areas.
Oregon
Climate Service - Extensive climate and weather information for the state
of Oregon.
Average
Last Frost Dates for New York- Average last frost dates for the state
of New York.
Echters Planting
Times - A chart of when to plant various plants (mostly flowers), based
on your local average last frost date. Shows exact dates for the Denver
Metro area, too.
Planting Times Chart - Colorado State University put
together this chart of the best times to plant vegetables based on the average
last frost date.
Hardiness Zones
Check out the sites below for information about USDA Hardiness Zones.
The
Garden Helper USDA Hardiness Zone - Find your USDA Hardiness Zone on
a map of the US.
Rockwell
Farms Hardiness Zones - A nice map of and general information about US
hardiness zones.
Plant Hardiness Zones in Canada - Canadian Maps!
NW & Alaska Charts
As noted above, the "Avg Last Frost" date is the date on which in half
of the previous years the last frost had already occurred. The "Safe
Date" is the day on which in nine of the previous ten years the last frost
had already occurred (only a 10% chance of a frost after this date).
Washington State
Location
|
Avg Last Frost
|
Safe Date
|
| Aberdeen |
April 10 |
April 30 |
| Anacortes |
March 22 |
April 16 |
| Battle Ground |
May 2 |
May 23 |
| Bellingham |
May 4 |
May 22 |
| Bellingham Airport |
April 21 |
May 6 |
| Bickleton |
May 30 |
June 23 |
| Blaine |
April 26 |
May 10 |
| Buckley |
April 27 |
May 14 |
| Cedar Lake |
May 2 |
May 21 |
| Centralia |
April 30 |
May 16 |
| Chelan |
April 16 |
April 30 |
| Chewelah |
June 3 |
July 1 |
| Chief Joseph Dam |
April 25 |
May 12 |
| Clearbrook |
May 3 |
May 22 |
| Clearwater |
May 7 |
May 28 |
| Cle Elum |
May 26 |
June 16 |
| Colfax |
May 14 |
June 2 |
| Colville |
May 17 |
June 7 |
| Concrete |
April 14 |
May 2 |
| Coulee Dam |
April 22 |
May 9 |
| Coupeville |
April 15 |
May 2 |
| Dallesport Airport |
April 16 |
May 2 |
| Davenport |
May 26 |
June 15 |
| Dayton |
May 4 |
May 28 |
| Diablo Dam |
April 21 |
May 5 |
| Elma |
May 7 |
May 26 |
| Elwah Ranger Station |
April 25 |
May 16 |
| Ephrata Airport |
April 21 |
May 10 |
| Everett |
April 9 |
April 30 |
| Forks |
May 12 |
May 28 |
| Glenoma |
May 11 |
May 30 |
| Grapeview |
April 13 |
May 3 |
| Hatton |
May 21 |
June 14 |
| Hoquiam Airport |
April 7 |
May 2 |
| Kennewick |
April 16 |
May 4 |
| Kent |
April 25 |
May 14 |
| Kid Valley |
May 8 |
May 27 |
| Lacrosse |
May 29 |
June 24 |
| Landsburg |
May 5 |
June 1 |
| Laurier |
May 24 |
June 13 |
| Longview |
April 22 |
May 11 |
| McMillin Reservoir |
May 4 |
May 25 |
| Monroe |
April 19 |
May 5 |
| Moses Lake |
May 7 |
May 25 |
| Mt Adams Ranger Station |
June 4 |
June 29 |
| Moxee City |
May 24 |
June 14 |
| Mud Mountain Dam |
April 28 |
May 10 |
| Newhalem |
April 8 |
May 1 |
| Newport |
June 7 |
July 9 |
| Northport |
May 11 |
May 29 |
| Oakville |
May 10 |
May 26 |
| Odessa |
May 20 |
June 7 |
| Olga |
March 29 |
April 21 |
| Omak |
May 14 |
June 1 |
| Othello |
May 6 |
May 24 |
| Palmer |
April 12 |
April 30 |
| Pomeroy |
May 7 |
May 24 |
| Port Angeles |
April 7 |
April 29 |
| Prosser |
May 4 |
May 21 |
| Pullman |
May 12 |
May 31 |
| Puyallup |
May 1 |
May 17 |
| Quilcene |
May 1 |
May 15 |
| Quincy |
May 3 |
May 18 |
| Rainier Paradise |
July 8 |
July 23 |
| Republic |
June 10 |
July 5 |
| Richland |
April 10 |
April 27 |
| Ritzville |
May 20 |
June 7 |
| Rosalia |
May 17 |
June 7 |
| Sea-Tac |
March 24 |
April 20 |
| Seattle UW |
March 22 |
April 15 |
| Sedro Woolley |
April 17 |
May 10 |
| Sequim |
April 14 |
May 3 |
| Shelton |
April 28 |
May 17 |
| Snoqualmie Falls |
April 29 |
May 21 |
| Spokane |
May 4 |
May 20 |
| Sprague |
May 23 |
June 13 |
| Stampede Pass |
June 2 |
June 24 |
| Startup |
May 4 |
May 24 |
| Stehekin |
May 8 |
May 26 |
| Sunnyside |
April 27 |
May 12 |
| Tacoma |
March 24 |
April 20 |
| Vancouver |
April 12 |
May 14 |
| Walla Walla Airport |
April 8 |
April 25 |
| Walla Walla |
March 27 |
April 19 |
| Wapato |
April 27 |
May 14 |
| Waterville |
May 17 |
June 5 |
| Wenatchee |
April 17 |
May 2 |
| Wilbur |
June 6 |
July 4 |
| Willapa Harbor |
April 20 |
May 12 |
| Wilson Creek |
May 18 |
June 4 |
| Winthrop |
May 28 |
June 18 |
| Yakima |
May 13 |
May 30 |
Oregon
Location
|
Avg Last Frost
|
Safe Date
|
| Antelope |
May 30 |
June 20 |
| Arlington |
April 19 |
May 7 |
| Ashland |
May 13 |
June 2 |
| Baker Airport |
June 3 |
June 29 |
| Baker |
May 30 |
June 20 |
| Bandon |
April 6 |
May 19 |
| Bend |
July 5 |
July 28 |
| Beulah |
May 23 |
June 6 |
| Bonneville Dam |
March 30 |
April 28 |
| Brookings |
February 28 |
April 12 |
| Chemult |
July 22 |
August 2 |
| Cherry Grove |
April 16 |
May 8 |
| Clatskanie |
April 15 |
May 4 |
| Cloverdale |
April 8 |
May 8 |
| Condon |
June 1 |
June 22 |
| Corvallis State College |
April 22 |
May 11 |
| Cottage Grove |
May 17 |
June 11 |
| Cottage Grove Dam |
April 20 |
May 8 |
| Crater Lake |
June 12 |
July 26 |
| Dallas |
May 9 |
May 29 |
| Dorena Dam |
April 26 |
May 13 |
| Drain |
April 25 |
May 23 |
| Dufur |
May 30 |
June 18 |
| Elgin |
June 12 |
July 8 |
| Elkton |
April 10 |
May 6 |
| Enterprise |
June 30 |
July 23 |
| Estacada |
April 13 |
May 5 |
| Eugene |
April 24 |
May 22 |
| Fern Ridge |
April 23 |
May 15 |
| Forest Grove |
April 27 |
May 15 |
| Fossil |
June 23 |
July 18 |
| Gold Beach Ranger Station |
March 2 |
April 12 |
| Grants Pass |
April 30 |
May 14 |
| Grizzly |
July 3 |
July 29 |
| Halfway |
June 11 |
July 3 |
| Hart Mountain Refuge |
July 7 |
July 24 |
| Heppner |
May 11 |
May 28 |
| Hermiston |
April 25 |
May 10 |
| Hood River |
May 5 |
May 23 |
| Huntington |
April 30 |
May 17 |
| Kent |
May 26 |
June 17 |
| Klamath Falls |
June 7 |
June 28 |
| LaGrande |
May 17 |
June 11 |
| Lakeview |
June 3 |
June 26 |
| Leahburg |
April 17 |
May 5 |
| Madras |
June 12 |
July 4 |
| Malheur Refuge |
June 6 |
June 25 |
| Marion Forks Fish Hatchery |
May 29 |
June 19 |
| McMinnville |
May 11 |
June 4 |
| Metolius |
June 12 |
July 3 |
| Mikkalo |
April 27 |
May 19 |
| Milton Freewater |
April 11 |
May 3 |
| Moro |
May 15 |
June 5 |
| Newport |
April 16 |
May 10 |
| North Bend |
February 28 |
April 11 |
| Ochoco Ranger Station |
July 13 |
July 31 |
| Ontario |
May 12 |
June 3 |
| Oregon City |
April 6 |
April 28 |
| Otis |
April 22 |
May 9 |
| Owyhee Dam |
April 29 |
May 15 |
| Paisley |
June 9 |
July 1 |
| Pendleton |
April 15 |
May 3 |
| Portland |
April 3 |
April 26 |
| Powers |
April 18 |
May 10 |
| Prineville |
July 2 |
July 25 |
| Prospect |
June 9 |
July 3 |
| Redmond |
June 18 |
July 9 |
| Redmond Airport |
June 23 |
July 17 |
| Reedsport |
April 7 |
May 10 |
| Richland |
May 22 |
June 12 |
| Riddle |
April 24 |
May 15 |
| Roseburg |
April 22 |
May 19 |
| Round Grove |
July 8 |
July 25 |
| Salem |
May 5 |
May 22 |
| Seaside |
April 14 |
May 2 |
| Seneca |
July 24 |
August 4 |
| Sexton Summit |
May 26 |
June 8 |
| Silver Creek Falls |
May 24 |
June 17 |
| Squaw Butte Exp. Station |
June 22 |
July 13 |
| Stayton |
April 24 |
May 13 |
| Three Lynx |
April 17 |
May 5 |
| Tillamook |
May 11 |
May 28 |
| Union |
May 24 |
June 12 |
| Vale |
May 13 |
June 2 |
| Wickiup Dam |
June 29 |
July 22 |
Idaho
Location
|
Avg Last Frost
|
Safe Date
|
| American Falls |
May 16 |
June 7 |
| Anderson Dam |
May 6 |
May 23 |
| Arco |
June 12 |
July 4 |
| Arrowrock Dam |
May 3 |
May 19 |
| Ashton |
June 15 |
July 7 |
| Avery |
May 21 |
June 14 |
| Bayview Model Basin |
May 29 |
June 18 |
| Bliss |
May 18 |
June 8 |
| Boise |
May 8 |
May 26 |
| Bonners Ferry |
May 16 |
May 29 |
| Burley Airport |
May 16 |
June 5 |
| Caldwell |
May 1 |
May 17 |
| Cambridge |
May 31 |
June 25 |
| Cascade |
June 19 |
July 12 |
| Callis |
May 28 |
June 24 |
| Chilly Barton Flat |
June 30 |
July 20 |
| Couer D'Alene |
May 11 |
May 26 |
| Council |
May 24 |
June 18 |
| Deer Flat Dam |
May 3 |
May 19 |
| Driggs |
June 18 |
July 7 |
| Emmett |
May 13 |
June 1 |
| Fairfield Ranger Station |
June 23 |
July 10 |
| Fenn Ranger Station |
May 1 |
May 18 |
| Fort Hall Indian Agency |
May 24 |
June 12 |
| Garden Valley |
June 2 |
June 27 |
| Glenns Ferry |
May 17 |
June 6 |
| Grace |
June 8 |
June 28 |
| Grand View |
May 8 |
May 26 |
| Grangeville |
May 25 |
June 12 |
| Grouse |
July 13 |
July 30 |
| Hailey Airport |
June 14 |
July 1 |
| Hamer |
June 13 |
July 7 |
| Hazelton |
May 13 |
May 28 |
| Hill City |
June 29 |
July 16 |
| Hollister |
May 28 |
June 15 |
| Idaho City |
June 25 |
July 15 |
| Idaho Falls Airport |
May 25 |
June 14 |
| Island Park Dam |
July 1 |
July 18 |
| Jerome |
May 14 |
June 1 |
| Kellogg |
May 16 |
June 9 |
| Kooskia |
May 12 |
June 3 |
| Kuna |
May 23 |
June 12 |
| Lifton Pumping Station |
May 18 |
June 5 |
| Mackay Ranger Station |
June 8 |
June 30 |
| Malad |
May 22 |
June 13 |
| Malad City Airport |
June 5 |
June 28 |
| May Ranger Station |
June 20 |
July 8 |
| McCall |
June 23 |
July 16 |
| Minidoka Dam |
May 15 |
June 7 |
| Montpelier Ranger Station |
June 16 |
July 5 |
| Moscow |
May 23 |
June 18 |
| Mountain Home |
May 20 |
June 9 |
| New Meadows Ranger Station |
July 2 |
July 23 |
| NezPerce |
May 24 |
June 16 |
| Oakley |
May 25 |
June 13 |
| Ola |
May 29 |
June 21 |
| Orofino |
May 1 |
May 17 |
| Palisades Dam |
June 2 |
June 24 |
| Parma |
May 12 |
June 2 |
| Paul |
May 19 |
June 9 |
| Payette |
May 10 |
May 31 |
| Pocatello |
May 20 |
June 12 |
| Porthill |
May 15 |
June 1 |
| Potlatch |
June 13 |
July 15 |
| Priest River |
June 3 |
June 30 |
| Richfield |
May 30 |
June 20 |
| Riggins Ranger Station |
April 23 |
May 14 |
| St Anthony |
June 4 |
June 29 |
| Saint Maries |
May 18 |
June 4 |
| Salmon |
June 2 |
June 26 |
| Sand Point |
May 20 |
June 5 |
| Shoshone |
May 18 |
June 7 |
| Swann Falls Powerhouse |
April 20 |
May 12 |
| Wallace Woodland Park |
May 25 |
June 13 |
Alaska
Location
|
Avg Last Frost
|
Safe Date
|
| Adak |
May 13 |
June 4 |
| Annette |
April 17 |
May 6 |
| Annex Creek |
May 13 |
June 7 |
| Barrow |
July 28 |
August 4 |
| Barter Island |
July 23 |
August 5 |
| Beaver Falls |
April 26 |
May 12 |
| Bethel |
June 1 |
June 21 |
| Big Delta |
May 20 |
June 3 |
| College Observatory |
May 30 |
June 17 |
| Cordova Airport |
May 25 |
June 8 |
| Eielson Field |
May 17 |
May 26 |
| Eklutna Project |
May 23 |
June 5 |
| Elmendorf Air Base |
May 4 |
May 15 |
| Fairbanks |
May 17 |
May 25 |
| Five Finger Light |
April 17 |
May 13 |
| Gulkana |
June 7 |
June 23 |
| Homer |
May 30 |
June 12 |
| Juneau |
May 16 |
May 30 |
| Kasilof |
June 9 |
July 1 |
| Kenai Airport |
May 29 |
June 12 |
| Ketchikan |
April 24 |
May 13 |
| King Salmon |
May 27 |
June 8 |
| Kotzebue |
June 13 |
June 24 |
| Little Port Walter |
May 8 |
May 22 |
| Matanuska |
May 23 |
June 1 |
| McGrath Airport |
May 23 |
June 2 |
| McKinley Park |
July 1 |
July 26 |
| Nome |
June 16 |
July 8 |
| Northway |
May 27 |
June 6 |
| Palmer |
May 18 |
May 28 |
| Petersburg |
May 16 |
June 5 |
| St Paul Island Airport |
June 18 |
July 9 |
| Seward |
May 7 |
May 17 |
| Sitka Airport |
April 21 |
May 7 |
| Sitka Magnetic Observatory |
May 20 |
June 1 |
| Talkeetna |
May 28 |
June 4 |
| Tanana |
June 6 |
July 3 |
| University Experimental Station |
May 29 |
June 10 |
| Wrangell |
May 5 |
June 3 |
| Yakutat Airport |
May 27 |
June 10 |
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