Crumble your cake into small bits and place in a bowl. Using a stand mixer, mix butter, confectioners’ sugar, milk, vanilla on medium speed. Gradually increase to high and beat until completely smooth.
Place a small amount of the frosting in a bowl and color it red. Color the rest with the Kelly Green gel food coloring.
Put 3 tablespoons of the green buttercream into your bowl of cake crumbs and mix.
Line a baking sheet with parchment paper. Form your cake into a cactus shape and then place the sucker stick into the shape. Let set in the freezer for about 15-20 minutes.
Once set, use Wilton tip #47 to frost each cake pop with green buttercream in an upward motion (ie.: vertical strips). Insert white sprinkles on random spots.
Using Wilton tip #191, frost flowers on top with red decorating frosting.