Arbor Day occurs in the United States every year on the last Friday in April. The customary observance is to plant a tree.

Similar holidays exist worldwide, some going by the same name, as in Australia, Canada, New Zealand and the United Kingdom, and is spelled Arbour Day.

State Arbor Days (state trees in brackets)

Alabama Last full week in February (Longleaf Pine)

Alaska Third Monday in May (Sitka Spruce)

Arizona Last Friday in April (Paloverde)

Arkansas Third Monday in March (Pine)

California March 7-14 (California Redwood)

Colorado Third Friday in April (Blue Spruce)

Connecticut April 30 (White Oak)

Delaware Last Friday in April (American Holly)

District of Columbia Last Friday in April (Scarlet Oak)

Florida Third Friday in January (Cabbage Palmetto)

Georgia Third Friday in February (Live Oak)

Hawaii First Friday in November (Kukui)

Idaho Last Friday in April (Western White Pine)

Illinois Last Friday in April (White Oak)

Indiana Last Friday in April (Tuliptree)

Iowa Last Friday in April (Oak)

Kansas Last Friday in March (Cottonwood)

Kentucky First Friday in April (Tulip Poplar)

Louisiana Third Friday in January (Baldcypress)

Maine Third full week in May (Eastern White Pine)

Maryland First Wednesday in April (White Oak)

Massachusetts April 28-May 5 (American Elm)

Michigan Last Friday in April (Eastern White Pine)

Minnesota Last Friday in April (Red Pine)

Mississippi Second Friday in February (Southern Magnolia)

Missouri First Friday in April (Flowering Dogwood)

Montana Last Friday in April (Ponderosa Pine)

Nebraska Last Friday in April (Cottonwood)

Nevada Southern: February 28;
Northern: April 23 (Singleleaf Pinyon)

New Hampshire Last Friday in April (Paper Birch)

New Jersey Last Friday in April (Northern Red Oak)

New Mexico Second Friday in March (Pinyon)

New York Last Friday in April (Sugar Maple)

North Carolina First Friday following March 15 ( Pine)

North Dakota First Friday in May (American Elm)

Ohio Last Friday in April (Ohio Buckeye)

Oklahoma Last full week in March (Eastern Redbud)

Oregon First full week in April (Douglas Fir)

Pennsylvania Last Friday in April (Eastern Hemlock)

Rhode Island Last Friday in April (Red Maple)

South Carolina First Friday in December (Cabbage Palmetto)

South Dakota Last Friday in April (White Spruce)

Tennessee First Friday in March (Yellow Poplar)

Texas Last Friday in April (Pecan)

Utah Last Friday in April (Blue Spruce)

Vermont First Friday in May (Sugar Maple)

Virginia Second Friday in April (Flowering Dogwood)

Washington Second Wednesday in April (Western Hemlock)

West Virginia Second Friday in April (Sugar Maple)

Wisconsin Last Friday in April (Sugar Maple)

Wyoming Last Monday in April (Cottonwood)