[Greenbuilding] best lumber for raised vegetable beds

[William R Bloom]

Be careful with the material you spec.


"Only materials made with either all plastic components or 
plastic and fiberglass will resist the elements outdoors 
for 200 years or more (the estimate for HDPE RPL or RPLs 
with HDPE and fiberglass).
These materials do not stain, warp, rot or take on 
moisture, or leach any chemicals. They are virtually 
non-reactive with water and other water-based solutions."

HDPE or high density polyethylene has poor UV resistance 
causing it to rot when exposed to sunlight.  It can be 
clad with a UV resistant cladding or otherwise stabilized. 
 The recreational vehicle industry learned this lesson in 
the 1960's when the exterior plastic fenders, exterior 
trim pieces and other parts began to rot off the sides of 
the motorhomes from sunlight exposure.  Its amazing how 
quickly this can occur.

Reference: 
  http://www.dynalabcorp.com/technical_info_hd_polyethylene.asp

I would assume/hope that the plastic lumber manufacturers 
use a stabilizing agent when forming their products. It 
wouldn't scare me away, but I would want to be sure its UV 
stable.