Answer: Usually moss will naturally appear in a spot to which it is suited, but you can try to encourage some by importing it. There are many different kinds of moss, and each one prefers a different type of growing location so you can't just try any old moss from, say, the woods. Find a location in your neighborhood with similar paving materials and exposure with moss and ask the owners if you could have some "starter" to use at your house. Some gardeners will bring it home in small chunks (it peels away like sod) and plant it between the stones, but to make a little bit go further some gardeners will mix the moss bits in the blender with buttermilk (and/or compost tea)and paint that along the areas where they want the moss to grow. Keep the area moist, and the moss should appear and multiply. I will warn you that it is better to use a ratty old blender for this operation as the moss tends to hold grit and will ruin the blade.
If your location is hot and sunny, moss may not grow there. You might need to consider some of the other plants suited to growing between stones such as the creeping and miniature thymes.
Have fun with your project!
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