South Dakota Codified Laws
Chapter 05 - Time And Dates
Section 1-5-10 - Arbor Day.

1-5-10. Arbor Day.
The last Friday in April of each year shall be set apart and established as "Arbor Day," or tree planting day, to promote and encourage the planting of trees in South Dakota. On this day and throughout the week, schools, civic organizations, communities, and all citizens and groups are urged to seriously consider the contribution of trees to the beauty and economic welfare of the state. Citizens are further encouraged to plant a tree and to properly care for the trees, shrubs, and other woody plants that provide many benefits to our citizens.

Source: SL 1998, ch 6, ยง1.