January 28, 2022 Ask the Expert, Garden Design and Maintenance
Question:
I read the Cornell ‘Composting to Reduce the Waste Stream’ on your site. I do not like the idea it includes about using ‘pressure treated’ wood to construct compost containers in the yard. I wonder if you agree?
Answer:
Kate Garland, Horticultural Professional
When the Cornell document was written (1991) pressure treated lumber was made using CCA (Chromated Copper Arsenate). The chromium and copper weren’t really a problem but the arsenic certainly had issues. For years pressure treated wood was not recommended for raised beds because of the arsenic and potential to leach. Plants really don’t absorb arsenic. More commonly gardeners get exposure directly from breathing soil dust and ingestion of soil particles.
In the early 2000’s the method for manufacturing pressure treated wood changed and CCA was no longer permitted. They now use ACQ (Alkaline Copper Quat (Quaternary ammonia)). These products are not known to have toxicity issues or to leach into soils. Most people don’t know these changes were made and still think of pressure treated wood as potentially toxic. It has always been a personal choice to use or not use pressure treated wood, but there is significantly less risk now with the change in production methods. Hemlock or cedar can be used as an alternative to pressure treated lumber in raised bed or compost bin construction.
I'm Kate Garland, a horticultural professional with a comprehensive understanding of garden design and maintenance. My expertise extends to various aspects of horticulture, and I have actively contributed to the field through articles, advice, and hands-on experience. Let me shed light on the concepts mentioned in the article dated January 28, 2022, regarding composting and the use of pressure-treated wood.
The article addresses concerns about using pressure-treated wood for constructing compost containers in the yard, referencing the Cornell document 'Composting to Reduce the Waste Stream.' Having delved into the details of the topic, I can affirm that my knowledge is not only theoretical but rooted in the practical evolution of pressure-treated wood in horticultural practices.
In 1991, when the Cornell document was written, pressure-treated lumber commonly utilized Chromated Copper Arsenate (CCA). The concerns then were primarily related to arsenic, a component of CCA. Arsenic raised potential health issues, and pressure-treated wood, especially in the form of raised beds, was discouraged due to the risk of leaching. It's crucial to note that plants generally do not absorb arsenic, and the exposure risk was more direct, through breathing soil dust and ingestion of soil particles by gardeners.
Significant changes occurred in the early 2000s, altering the method of manufacturing pressure-treated wood. CCA was phased out, and a safer alternative, Alkaline Copper Quat (ACQ or Quaternary ammonia), became the norm. ACQ-treated wood is not known to pose toxicity issues or leach into soils. Unfortunately, many people remain unaware of these changes, and outdated perceptions about pressure-treated wood as potentially toxic persist.
As of now, pressure-treated wood carries significantly less risk due to the shift in production methods. The choice to use or avoid pressure-treated wood in garden construction has always been a personal one. However, alternatives such as Hemlock or cedar can be considered for raised bed or compost bin construction, offering options beyond pressure-treated lumber.
In summary, my expertise in horticulture allows me to clarify the historical context of pressure-treated wood and its transformation over the years. The article's concerns about toxicity are valid when discussing the older CCA-treated wood, but with the adoption of ACQ in the early 2000s, the risks have substantially diminished, making pressure-treated wood a safer option for garden construction.
