Makes: 10 servings. Prep: 1 hour. Bake: at 350° for 60 to 70 minutes.
Heat oven to 350°F.
Turn flowerpot, bottom up, on counter. Center large-enough piece of extra-wide, heavy-duty aluminum foil over bottom of pot to cover sides of pot, with plenty of overhang. Press foil gently to entire outside of pot to shape foil. Remove foil. Invert pot; place shaped foil inside pot, gently easing foil into pot and covering all surfaces. Gently press foil against sides of pot to flatten all creases. Fold excess foil over top and press firmly to outside of pot, anchoring under flowerpot rim. Coat foil inside pot with nonstick cooking spray.
Prepare cake batter following package directions. Remove 1 cup batter to make 3 x 1-1/2-inch cupcakes. (Full amount of batter would overflow pot during baking.) Pour remaining batter into prepared flowerpot. Smooth top with spatula.
Bake in 350°F oven 60 to 70 minutes, until wooden pick inserted in center tests clean. If top browns too quickly, cover loosely with foil. Cool in pot on wire rack.
When completely cooled, lift foil with cake from pot. Remove foil. Place cake, top up, on serving plate. Trim top flat with serrated knife. Create pot rim: 1-1/2 to 2 inches down from top, with small knife, cut in 1/2 inch, then down to cake bottom at tapered angle. Crumble trimmings; reserve 1/2 cup for dirt.
Tint frosting with desired color. Frost cake. Sprinkle top with reserved cake crumbs. Arrange flowers and leaves in pot. (Use any leftover frosting to decorate cupcakes.)