Arbor Day

Arbor Day (from the Latin arbor, meaning tree) is a holiday in which individuals and groups are encouraged to plant and care for trees.
It originated in Nebraska City, Nebraska, in the United States in 1872.
J. Sterling Morton is the founder of Arbor Day.
The first Arbor Day was held on April 10, 1872, and an estimated 1 million trees were planted that day.
Many countries now observe it on various dates, depending on climate and suitable planting season, usually in the spring.

Portugal
Arbor Day is celebrated on March 21. It's not a national holiday but instead schools nationwide celebrate this day with environment-related activities, namely tree planting.

United States of America

Arbor Day community festival in Rochester, Minnesota.

 

By the 1920s, each state in the United States had passed public laws that stipulated a certain day to be Arbor Day or Arbor and Bird Day observance.
The national holiday is celebrated every year on the last Friday in April; in Nebraska, it is a civic holiday. Each state celebrates its own state holiday. The customary observance is to plant a tree.


Source: Wikipedia