Plank's Groovy Arbor Day Party is an annual party Jonny and Plank have every year to celebrate their favorite holiday, Arbor Day. It was first and only seen in the episode "Tween a Rock and an Ed Place". During the party they play several small, nature-themed, party games, much to Eddy's disliking.
It is sometimes not celebrated on the real Arbor Day for Edd tried to tell Jonny the party was six months off. Even if Jonny said everyone comes to the party, the other kids most of the time have something else to do (or just try to avoid it). Some of the games played at the party are "Oak, Oak, Spruce" (based on Duck, Duck, Goose), "Guess how many seeds are in the jar," listening to Plank's jokes, and "Make a Wish on the Awesome Arbor Day Acorn." When the Eds went to wish on the "Awesome Arbor Day Acorn," Ed (and Plank) had made a wish on the acorn that they would party forever, which Jonny took easily.
They would then become the "Arbor Day Daisy Chain of Woodland Buddies" who watch over the "Arbor Day Youngling" until it grows into a full grown tree, Plank would then play "Ode to Margot" and "Watson's Waltz" to the tree when it finished growing.
- Jonny and Plank claim the party is very popular, but the Eds were the only ones who ever showed up because all the other kids had other stuff to do--most of which seems to have been made up for the purpose of avoiding him.
- Eddy apparently prepared a tape called "Eddy Entrance Mix" for when he makes an entrance into parties.