Arbor Day (or Arbour; from the Latin arbor, meaning tree) is a holiday in which individuals and groups are encouraged to plant and care for trees. Today, many countries observe such a holiday. Though usually observed in the spring, the date varies, depending on climate and suitable planting season.
The first American Arbor Day was originated in Nebraska City, Nebraska, United States by J. Sterling Morton. On April 10, 1872, an estimated one million trees were planted in Nebraska.
Birdsey Northrop of Connecticut was responsible for globalizing it when he visited Japan in 1883 and delivered his Arbor Day and Village Improvement message. In that same year, the American Forestry Association made Northrop the Chairman of the committee to campaign for Arbor Day nationwide. He also brought his enthusiasm for Arbor Day to Australia, Canada, and Europe.
Nebraska, Ohio: Last Friday in April.
Wisconsin Public School Observance Days: April 29.
California education holidays: March 7.
Source: wikipedia.org
In 2018 Arbor Day in USA falls on April 27.