From Abe: “We really like this method of building. We put a 35 feet wall up in two days with three people, excluding the stucco and plaster. It was also very cheap. We do not yet know the durability of this method, as we are the first that we know of to have used it. Time will tell, but it certainly seems very sturdy and has not shifted at all in the six months it has been standing.
Preparation: For a foundation, dig a trench and fill with gravel or rubble. Its width needs to be wider by a few inches on either side than your wall will be. The fact that you do not need a concrete foundation is one of the reasons that makes this method so cheap.
Posts: Place posts every two or three feet on either side of your wall. You want the posts of one side of the wall to be directly opposite the posts on the other side of the wall. Make sure the posts are not leaning outwards. They can however lean in towards each other a little.
We have used metal pipes as posts as well as Juniper limbs. The advantage with the metal is that you can hammer them into the ground quickly. Tree limbs are much cheaper (in our case free), but you have to dig a hole for them. With short retaining walls that are only a couple of feet tall, you can use rebar – cheap and easy to pound into the ground.
The type of post you use is not that important, so pick one that suits your purposes: cheap, easy, decorative.”