Today is Arbor Day, which marks a tree-planting holiday founded in 1872. It's annually celebrated on the last Friday in April.
The Arbor Day Foundation's website, which you can access by clicking on the link that accompanies this page, offers Arbor Day history as well as free Arbor Day e-cards.
"Happy Arbor Day" might be the one celebratory message that can't be interpreted to mean "I love you" or "let's get married."
Then again, maybe I'm wrong.