National Arbor Day is the Tree Planter's holiday, and has been celebrated since 1872. It began in Nebraska, a largely treeless plain back in the 1800's. It is a day to plant and dedicate a tree to help nature and the environment. Millions of trees are planted on this day.
The National Arbor Day Foundation provides millions of trees for planting. It is estimated that 18 million tress are planted each year on Arbor Day.