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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

Alaska   Idaho   Oregon   Washington

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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