Moss Graffiti

Popular Mechanics has a neat little guide that shows you how to make moss graffiti:

Ingredients: 

• 3 handfuls moss (get it for free from a forest, off a tree or your yard)
• 3 cups lukewarm water
• 2 tablespoons (tbsp) gardening water-retention gel
• 1/2 cup buttermilk

Additional Things You'll Need:

• Blender
• Bucket
• Wood or concrete surface
• Paintbrush
• Spray bottle

  Directions

1. Crumble three handfuls of moss, 3 cups of lukewarm water, 2 tablespoons of gardening retention gel and 1/2 cup of buttermilk into a blender.
2. Pulse the ingredients in the blender for 2 to 5 minutes so a gel forms. 
3. Pour the mixture into a bucket.
4. Paint the mixture onto a wooden or rough concrete surface. To make a fancy design, draw it onto the surface first and paint the moss mixture over the drawing (stay inside the lines).
5. Mist the moss with water on the same day every week and watch the graffiti grow. The amount of time it takes for the graffiti to grow depends on the the type of moss you used and the weather conditions. 

Here's an example of someone using a stencil to make moss graffiti:

By Bündnis 90/Die Grünen Baden-Württemberg

The finished product:

By Bündnis 90/Die Grünen Baden-Württemberg

If this person filled the stencil with more moss, the letters would have looked more solid. 

You can find this project in the book More Show Me How: Everything We Couldn't Fit in the First Book Instructions for Life from the Everyday to the Exotic.

The book

Water-retaining gel for gardening