Raised Bed Organic Gardening
We want to grow vegetables in boxes on our deck. Would pressure treated wood lined with food grade plastic be safe? What would be the best materials to use to prevent leeching of toxins into the soil?
It is wonderful to see you have done your homework and are concerned about the use of pressure treated lumber. The scientific community has consensus that the chemicals do leach out of the wood into the soil and are uptaken by the plants in very small amounts. The primary concern in using pressure treated wood was with those treated with CCA (chromated copper arsenate). Arsenic was the problem and in 2003 the EPA banned CCA pressure treated lumber for consumer use. Pressure treated lumber manufactured for consumer use after that date does not have arsenic in it. You can as you pointed out line your beds with landscape fabric/plastic before filling it with soil. For additional information on pressure-treated lumber, check out the publication by Pennsylvania State University entitled "Garden Uses of Treated Lumber" (http://pubs.cas.psu.edu/freepubs/pdfs/uc173.pdf) as it does a good job describing the risks of using both CCA-treated wood as well as new ACQ-treated wood.
Alternatives to using pressure treated wood include: Naturally resistant types of wood, including cedar, redwood, and juniper;Lumber treated with less toxic solutions, particularly those containing copper and boron; Synthetic lumber, including those made from recycled plastics or rubber or Concrete blocks and other inorganic structural materialsEnjoy your new raised beds.