Ingredients

• The three most common treatment ingredients for landscape timbers include creosote, pentachlorophenol and leach-resistant salts known collectively as chromated copper arsenate, or CCA. Creosote and pentachlorophenol both tend to emit an unpleasant petroleum smell and an oily residue on hot days, unlike CCA.
  
  

Methods

• Manufacturers use a variety of methods to treat landscape timbers. Pressure treatment forces the preservative deep into the wood. Non-pressure methods include vacuum, thermal, double diffusion or cold-soaking treatments.
  
  

Safety

• In response to concerns over the possibility of arsenic leaching from landscape timbers treated with CCA, researchers at North Carolina State University sample a pair of such gardens intermittently to compare findings against control samples. The results indicate that some arsenic escapes from the timbers but doesn't travel more than a few inches.