I suspect that Arbor Day, as it was when I was a child, is a holiday most familiar in the elementary schools of America, since it does not involve grownups getting the day off from work, except in Nebraska (not a state famous for its orchards and forests). On a (hopefully) sunny day at the end of April, fourth or fifth or sixth-graders go outside and either help plant a tree, or watch other people plant one. That’s the way I recall the process, anyway.
It wasn’t until recently, though, that I learned that it was President Nixon who standardized observance of Arbor Day by proclamation in 1970, fixing it on the last Friday of April. Here’s an article about the ways in which the day is observed.