DIY - Glow in the dark pots with mums for fall/Halloween. Buy a flower pot that you really like and use Rustoleum's Glow-in-the-dark paint to paint the pot. During the day, the paint will absorb the sunlight and at night the pots will glow.
Insect hotel - Sustainable ideas including an explanation of the materials used, which insects they provide a habitat for and why you want that insect. This would be perfect to have as a project to build with a youth program