Iowa Code § 1C.10: Arbor Day and Week.

The last Friday in April in each year shall be observed in Iowa as Arbor Day and the week in which this Friday falls shall be observed as Arbor Week. This day and week shall be designated annually by the governor with suitable proclamation urging that schools, civic organizations, governmental departments and all citizens and groups give serious thought to and appreciation of the contribution of trees to the beauty and economic welfare of Iowa.