First off, this is _not_ a joke. We used to grow these things when I was a wee linoleum lizard in Pennsylvania.

The following is the recipe for "growing" a coal garden:

Piece of coal. (I think we always used anthracite--but that may've been just a regional thing. Bituminous may work just as well.)

1 cup water.

6 tablespoons salt.

4 teaspoons ammonia.

A few drops of food coloring (any color.)

I had actually lost this recipe for over twenty years. (!!) I found it again when I was packing my stuff up for the move to Al-ass-ka.