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Raised Garden Beds can be made from various timbers. The Timbers used need to be resistant against insect attack, fungi, termites and wood boring insects. 

Most of the timber I use in my garden beds is pine or cypress pine.  Normal pine is less expensive compare to cypress pine and suits our clients requirements. 

Normal pine is treated to protect against insect attack.  

There are two types of treated pine available:-

1/. CCA -  Copper, Chromium and Arsenic salt. CCA is a water-borne preservative treatment of pine timber. CCA is pressure impregnated into the wood and has a high resistance to chemicals leaching out of the timber over time. This high resistance is due to the chromium which locks in the elements of copper and arsenic into the wood.  

2/. ACQ -  Alkaline Copper Quaternary. ACQ is a water-borne preservative treatment of pine timber. The ACQ treatment process is similar to CCA but is free of arsenic. Instead uses copper and ammonium compounds as agents against insect attack, fungi, termites and wood boring insects. 

So which is best for your garden?

There are a few schools of thought on the safety of Treated Pine and the available information is sometimes conflicting.  Normal treated pine is treated with Copper chrome arsenate (CCA) a preservative containing copper, chromium and arsenic. There is speculation that the arsenic salt can leach into soil and possibility into your vegetables. The Timber Preservers Association of Australia advise that CCA Treated Pine isn’t a concern in gardens. Their research has shown that preservatives like CCA are not absorbed into grapes, tomatoes and cucumbers but they do admit some root crops like carrots and beets have been reported to pick up small amounts of arsenic. However this trace amount is said to be an organic, non-toxic form, i.e. not harmful and in any case is largely removed by peeling the vegetable. Precautions, such as lining the garden bed with plastic or painting the inside will eliminate any concerns.

ACQ on the other hand, is a waterborne form of timber treatment that was developed as a safer alternative to the widely used CCA preservative. Also designed to be used as an insecticide        and fungicide. This is a safer option if using CCA wood in your vegetable gardens is a concern.

What is the cost difference? ACQ is typically 15-20% more expensive than CCA Treated Pine.