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The intended use for these troughs is for dwarf conifers and alpine plants. Alpines thrive on a very lean soil mix and excellent drainage. Therefore the troughs are filled with a mix that contains only 20-30% of actual topsoil. The remainder is made up of #2 chicken grit, lime chips or pea rock and some sphagnum moss. The top 1 or 2 inches might be all rock or #3 chicken grit (also called rubystone). Richer pockets of soil can be created for placing dwarf conifers. Before filling the trough, cover the drainage holes with plastic needlpoint mesh.
For sources for dwarf conifers and alpines, see our Dwarf Conifer page. A mail-order source for heaths and heathers is Rock Spray Nursery / Box 693 / Truro MA 02666 / 508-349-6769. If you're within driving distance of the Twin Cities, Rice Creek Gardens, Inc. is worth a stop. Their address is 11506 Highway 65 / Minneapolis MN. Unfortunately, they don't ship.
In our climate - USDA zone 4 - these troughs may be left outside for the winter with a little protection. They can be placed in a depression in the soil and covered to protect from excess moisture. Too much moisture is more of a concern than the cold. They can also be kept in an unheated patio or garage.
Using a search engine to look for "hypertufa troughs" will probably yield more results than you thought possible. Here are a few links to start with:
http://www.backyardgardener.com/tufa.html
http://www.suite101.com/article.cfm/enabling_garden/2185
http://www.evergreenshowplace.com/9802tufa.html (What the heck is hypertufa?)