Gardening and Horticulture - Raised bed material

Hi, I've been doing organic raised bed gardening for some time now without using any retaing walls. I'd like to install some, but don't want to waste money on stuff that will rot or poison the soil. Was thinking about TREX decking boards. Anyone ever use this stuff, or is there something better????????jim

Raised beds work fine without being walled in. Soil is tilled and raked to at least 6" deep. If wanting to wall in, you can use stone, brick, or rot-resistant lumber such as red cedar. Treated lumber is not recommended for vegetable gardens because it tends to leach heavy metals in soil. Trex is a wood and plastic composite material. Manufacturer claims that it can be used as landscaping timbers and have ground contact and that it is highly resistant to decay and insects.

Actually I only have one area that I want to raise a little higher for my Asper-grass. Think I'll give ol'Trex a try. Thanks.....jim