Do you need to use only treated wood when making outdoor decorations?

Most of those retro custom plywood made Christmas decorations and custom birdhouses are made out of untreated wood thats been carefully sanded primed and sealed. The process is much like making a corn-hole set.

There are better grades of wood to use like premium grade 1/2" exterior birch which is not your typical plywood. This provides a smooth finish for application that will several years. Outdoor pieces need to be sanded & sealed prior to painting, then coated with a clear Spar Urethane spray. Upkeep - resealing over the years as winter exposure may be needed.

http://homeguides.sfgate.com/diy-wood-yard-decorations-53307.html

Thank you Janet! I will definitely use this as a resource! !