“Once you have selected your site, you need to choose your stones. Look for rocks with angular faces—they stack better and a give a firmer repose. Rounded rocks are almost impossible to build into a wall without using copious amounts of mortar. An ideal rock has six parallel faces (like a brick). Regretfully, there aren’t many ideal rocks available, so look for angular rocks with the most flat faces.
To figure out how much stone you’ll need, multiply your wall’s height times the depth times the length. If your wall is 2 feet high, 1-1/2 feet wide, and 20 feet long, you’ll need roughly 60 cubic feet of stone. Most stoneyards will deliver the stones for a slight charge; have them placed as close to the site of your retaining wall as possible.
Walls are built in courses. The base course is structurally the most important, while the final course, the capstone, is the most challenging. For stability, walls should be at least 20 inches wide at the base. They can taper slightly toward the top, but you’ll want a wall that is at least two rocks wide in most places. This can be accomplished by mixing stones of different sizes or by backfilling with a combination of two-thirds rubble to one-third soil.”
Read the full article at the source: Fine Gardening.com
(This site is part of Taunton Press, the publishers of Fine Woodworking and Fine Homebuilding magazines that I mentioned a while back. Their publications are always excellent quality and value.)
Don’t have the squarish/angular stone for building dry-stacked walls? Try this other method, also by Fine Gardening.com: Planted Pockets Give Life to Stone Wall