Many gardeners growing in a raised bed ask “Is pressure treated wood safe for vegetable gardens”?
They fear the chemicals used in the treated wood of the raised bed will leach into the soil and the plants.
Many years ago, gardeners embraced the introduction of pressure-treated lumber impregnated with CCA (chromated copper arsenate) as a dream come true. It boasted longer life than untreated wood and improved longevity than the rot-resistant species such as redwood.
This pressure treated lumber was so popular you could buy them almost anywhere. Manufacturers claimed the chemicals used to treat the lumber, though toxic, couldn’t find their way to the soil.
The main advantage for the gardeners was that the chemicals were “harmless” to plants, unlike the previous popular wood preservatives – pentachlorophenol and creosote.
Word started leaking out that the CCA-treated wood was not so safe after all. Reports circulated that the chemicals found their way into the soil, which set off a debate on the use of pressure treated lumber for the garden.
What Compounds Are Used For Treating Pressure Treated Lumber?
The pressure-treated lumber can be non-toxic or toxic. It depends on the preservatives used to treat the wood. Wood treated with CCA or chromated copper arsenate can leach arsenic, a very toxic compound.
Plants growing in the garden bed may take up the chemicals. CCA-treated lumber shouldn’t be used for raised beds and restricted to construction work only. Avoid wood treated with black creosote, a smelly coal tar derivative as well.
Copper based wood preservatives began more widespread use in 2013 with compounds such as:
- Copper azole (CA)
- Micronized copper quaternary (MCQ)
- Alkaline copper quaternary (ACQ)
Copper is considered less toxic compared to arsenic.
Manufacturers of pressure-treated wood with micronized copper quaternary claim that their lumber won’t leach any copper into the soil and therefore, it’s safe for all uses, including making garden beds.
Copper Azole and Alkaline copper quaternary contain fungicide and copper but not arsenic. The copper works to deter insects while the fungicide prevents soil fungus from attacking the lumber. Copper It is also used as a fungicide on food crops.
The copper-based preservatives are considered safer as virtually all the preservatives used are also used in other home uses such as growing food crops and in swimming pools.
For those who still don’t feel safe using these treated woods for a raised bed you can use decay-resistant lumber or line the interior walls of the raised garden with a heavy plastic sheeting.
However, for those who want to grow organic foods, do not use pressure-treated lumber. If you want to grow pure organic foods that meet high standards and purity, choose a different material.
How Safe Is Pressure Treated Lumber?
Claims have been raised. Some claims backed by scientific facts while some not yet proven. If your raised garden bed uses arsenic-treated wood, don’t panic. Plants will not take up the arsenic leached into the soil unless they are deficient in phosphorous. This is not a problem for those who use compost frequently and generously.
The risk is minimal with the new copper-based wood treatments. Plants which take up too much copper will die before they mature. Plus, these homegrown vegetables make up a minuscule percentage of the daily diet, making exposure to copper intake insignificant. However, researches are ongoing to determine the extent of the copper leaching into the soil.
“Though actual cases of poisoning via pressure treated wood use by the public were hard to find, there was enough circumstantial evidence of soil contamination to warrant a change.” via naturalhandyman.com
To be on the safer side, line inside the pressure-treated wood with heavy plastic. This helps prevent the leaching of chemicals from the wood into the garden soil. You can also do away with the treated wood and use alternatives, such as concrete blocks, composite wood made from recycled plastic or decay-resistant wood like western red cedar and redwood.
The decision is up to you; since all these claims are not yet justified. You can decide whether to use the pressure-treated lumber or not. We’ve given you the facts.
NOTE: We used truckloads of pressure treated lumber in the nursery of my 4 decades of growing plants and never experienced any problems. However, you be your own judge. For more details and answers on the topic via PennLive