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May 23, 2007

Pressure-treated wood and gardening: newer solutions

First, some background: Does Pressure-Treated Wood Belong in Your Garden? is a dated (1998) survey of earlier choices. (It's from Kitchen Gardener, which is no more, online at Fine Gardening, both by Connecticut's Taunton Press.) It begins,

A couple of decades ago, lumber impregnated with chromated copper arsenate (known as CCA) was considered the answer to a gardener's prayer. It boasted longer life than rot-resistant species like redwood, you could buy it almost anywhere, and manufacturers said the treatment chemicals, though toxic, safely stayed put in the wood. The main plus for gardeners was that the chemicals didn't harm plants, unlike creosote and pentachlorophenol, two previously popular wood preservatives.

But then word started seeping out that those CCA chemicals weren't so perfectly bound up after all, that some of them, in fact, migrated from the wood into the surrounding soil. And that's when pressure-treated wood moved into the hot seat...

The problem was... arsenic.

Then ACQ (from the EPA: ACQ - An Alternative to CCA)came along, adding 10 percent to the cost of treated wood, but arsenic-free. But it corrodes aluminum. (We built a deck a few years ago and used ACQ-treated Philippine mahogany (meranti) from Douglas Lumber. We did have to use stainless steel for all the fasteners.)

But now there's another choice. In Pressure Treated Wood And Gardening, at New Jersey blog Compost Bin, blogger Anthony writes,

I received a really interesting comment the other day on an old post about building raised garden beds. The commenter works in the pressure treated wood industry and really provided a great explanation of the types of wood that are available and what's in store for pressure treated wood in the future.

The commenter reports on "the new kid on the block":

You will see it as a few different names: MCQ, Smart Sense, MicroPro, MicroShades, or Micronized Copper Quaternary. ACQ is held in solution, a liquid. MCQ is chemically different. It is made of tiny (micro) particles of copper. These particles are forced into the wood cells or pores during the pressure cycle. Once in, they stay in, also forming a barrier keeping in the quaternary. The leaching of chemicals out of MCQ is practically non-existent. So much so that aluminum is actually approved for use on this type of treated wood.
It just started going into production the end of 2006, and is becoming available in almost all states. If you can not find it, request it, or shop somewhere they do carry it. Most of the independent lumber yards will carry it, and Home Depot has it available in some stores as well.

To add a side note, I purchase organic and/or natural produce when available. I did not want to use ACQ in my organic raised bed garden, if I had to, I would have use a liner. However, I am building raised beds this year, and dragging my feet paid off this time, because MCQ became available, and I trust the research behind this product. ACQ was the step away from CCA, MCQ is the step up to a new level of safer treated products.

Have you seen it? Tried it? Collectively, what do we know about it?

Related: For those who prefer to treat their own wood, here's the recipe we used to treat the old oak floor beams from which our raised bed is constructed.

Posted by Sheila Lennon at 10:20 AM | Permalink

May 23, 2007

Pressure-treated wood and gardening: newer solutions

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