I went to a seminar by Janit Calvo, owner since 2001 of the miniature garden center; www.twogreenthumbs.com.  She creates containers that make a 6 inch tree appear like a 60 foot giant.  She adds plants with extremely slow growth rates, some less than an inch per year.  She uses a variety of shapes and sizes to mimic a real life size garden.  She adds hardscape, like stone or brick patios, birdbaths and benches to give it a feel of reality.  They are so cute!  And these gardens are designed to last for years.  For groundcovers she uses almost any small-leafed plant chosen for good behavior (keep your roots to yourself!) and easy maintenance.  The trees are what fascinated me.  I can’t quite figure out how these miniature conifers grow so slowly.  Plants usually want to grow and go, unless they are in a harsh environment, but these stay compact.  I wonder what their life expectancy is?  Plants like Canada Hemlock ‘Minuta’ or ‘Abbott’s Pygmy’ or Hinoki Cypress ‘Nana’ or ‘Gemstone’, Mugo Pine ‘Mitsch Mini’ or ‘Teeny’ to give a few examples.  She has a complete list on her website.