Recycled Plastic Fence Post for Garden beds.
http://www.durgan.org/ShortURL/?LXWIS 2 October 2008 Recycled Plastic Fence Post

A friend had a number of these recycled plastic composite fence posts, and donated them to me for containing a garden bed. They are held in place with two foot, iron, half inch diameter, rebar through holes drilled in the posts.The black posts are 5 inches in diameter, and 8 feet long. The posts are easy to hand saw, and are about the same weight as two mini ties of the same length. I know nothing about the cost, or even where to purchase them at this time.

I have been using wooden mini ties, but these fence posts would appear to be a fine replacement, since they will not deteriorate over time. The black colour also is not as obtrusive to the view, since it fades into the dark soil.