1 wide shallow dish
1 large lump or 2 or 3 small lumps of coal
6 bluing
6 T salt
6 T water
1 T ammonia
food colorings

Wash coal thoroughly; place in center of dish. Mix together well the bluing, salt, water and Ammonia; pour over coal, making certain that all areas of the coal have been moistened. Let stand undisturbed; the "flowers" will start "growing" within a few hours. At this point a few drops of various food colors may be dropped on the crystals to make a more colorful garden. If not jolted, the "garden should flourish for two Weeks, Or longer.
 

Source: Louise Jones