Treated Wood

redrabbit(Pgh Pa)November 2, 2013

I would like to build some above the ground boxes for my tomatoes and pepper plants. I know the best wood would be cedar,but its very expensive. I have some old treated ( wolmnized) decking I would like to use. Should I be scared of the chemicals that were used in its treatment ??? These would be built on legs about 3 feet above the ground.Thanks in advance...

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seysonn(8a WA/HZ 1)

How old are those decking lumber ? I think the recent pressure treated woods are safe.

But not all cedars are pricey. Maybe it is where you are.

I buy these cedar boards 5 1/2 by 6ft, 9/16" thickness for about. $1.50 from Lowes and HD. With 6 of those(double stacked) I make a 3ft by 6ft raised bed. That is ten buck, plus screw and corner pieces ... FOR UNDER $15.00. That is about 80 cents per sqr-ft of raised bed. I spent roughy the same amount for top soil and compost. That added up to about $1.50 per sqr-ft , complete. Of course not counting my time and labor.

    Bookmark   November 2, 2013 at 9:12AM
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nil13(z21 L.A., CA (Mt. Washington))

old pressure treated probably has arsenic and isn't safe.

    Bookmark   November 2, 2013 at 11:43AM
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The CCA treated lumber that was removed from the market offers minimal hazards to a raised bed. For one, the amount of arsenic that leaches into the soil from this product is not very significant (and arsenic IS present in soil anyway) and tends to be concentrated immediately adjacent to the wood frame. And two, there is no evidence that plants take up these heavy metals into their tissues so transference from the soil to your table is unlikely to occur. One can always line the beds with plastic to prevent any leaching if you are really concerned.

There is far greater risk of harm occurring from CCA treated lumber by direct contact, as in its use for a deck, railing or playground equipment or sawing or burning the stuff.

    Bookmark   November 3, 2013 at 4:36PM
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redrabbit(Pgh Pa)

Thanks a lots for the advice. The only cedar I found at Home Depot was $20.00 for one piece 8" by 8' .I think I will go with Gardengal advice. I have a lot of old decking probably 20 years old that look super after its run thru a planer. Thanks again

    Bookmark   November 3, 2013 at 8:53PM
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seysonn(8a WA/HZ 1)

here @ PNW we have abundant of cedar. The One I have used are the same(very similar) to those used to make privacy fence. They have also the kind you mentioned in another isle. Those are TOO expensive to me. Both HD and Lowes carry a lot of cedar lumber. Some of they are fresh out of mill and still wet. May be they don't have them in PA.

In this case you have to get pressure treated wood. They also have this landscaping timber, with redish color. You will need to stack about 3 of them to get a height of about 10 inch. To hold them together , you will need to drill hohes in them ( 1/2" at about feet apart)t and drive rebars through them. An 8' length costs about $3.50. With 9 of of them you can make s 4 by 8 bed: That is about one buck per square foot of bed. Not bad. A lot of people use them to make raised bed.

    Bookmark   November 4, 2013 at 4:28AM
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calistoga_al ca 15 usda 9

I have used a lot of pressure treated lumber for raised beds, as well as for decking with no problems. In my experience the lumber must be secured in place immediately when purchased or it will twist as it ages, making it difficult to use. For you to have old saved timber and been able to run it through a planer surprises me, congratulations. Al

    Bookmark   November 4, 2013 at 9:38AM
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nil13(z21 L.A., CA (Mt. Washington))

Pressure treated wood is usually only treated on the surface down to about an 1/8th inch into the wood. That is why you also have to treat the cut ends with a preservative. If you plane that off, it is just bare wood.

    Bookmark   November 4, 2013 at 10:55AM
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nil13(z21 L.A., CA (Mt. Washington))

I also hope you were wearing a respirator when you planed those boards.

    Bookmark   November 4, 2013 at 10:57AM
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rebuilder(7a-7b Snellville, GA)

Just to further clarify treated wood products and their toxicity. There are many treatment methods. CCA (chromated copper arsenate) is the oldest method and is only used in industrial settings now. ACQ (Alkaline Copper Quaternary) which combines copper along with a bacterial/fungicide (quaternary ammonium compound ). I use the ammonium quats for mold remediation and they are quite safe. So far most authorities regard ACQ as safe for gardening. There are perhaps another half dozen methods as well but are not as widely used. Here's a pdf with a better description:

The Yellow Wood brand here in the south uses a micronized copper which is also safe. In other parts of the country there may be other treatments used depending on the wood species and availability and regional perceptions of safety. Most folks agree that old weathered CCA lumber is also safe for gardening. I don't think the OMRI allows any treated lumber or organic certification. It seems there are two schools of thought about using a polyethylene plastic barrier between the wood and soil. Personally I would use plastic just to keep the wood a bit dryer unless water can get in from the top plus if you are skeptical about chemical exposure then you have a barrier(other than worrying about chemicals leaching from the plastic).

One other thought is about the treatment process and exposing the center after a cut. At least in the south this has never been a problem even though the industry has told us to coat the ends with a wood preservative for the last 50 years. I've never had any ends rot(CCA) after as long as I've been in construction(35 years) unless it was buried in the soil. Even still I've had very few with extensive rot that was in contact with soil. I will say that the newer treatments don't last as long as CCA. I've had some with the latest treatments that have had at least some rot in as little as 5 to 10 years if they were in direct contact with soil. Most haven't.
The most common treatment process uses a vacuum chamber to evacuate extra water from the cells then the chamber is flooded under pressure with the treatment chemicals. Some newer treatments may only use pressure. Most of the time the chemical reaches the center unless the middle is dense heartwood which is rot resistant anyway.

I use a lot of copper naphthenate (sometimes available at the big box stores) to coat raw wood that may be exposed to some moisture and have found it to be a great wood treatment. It soaks into the wood about 1/8 to 1/4". I mostly use it for exterior rot repairs but I also use it for some of my wood containers and decorative wood baskets with pots. The containers that I've treated are still in great shape after 5 or so years. Just don't get it on your skin because the odor will stay with you for 12 to 24 hours after washing.

Most treated wood is not rated for ground/soil contact unless they are 6x6 or larger with some exceptions and special orders. Most 4x4's that folks used for direct burial fence posts are not rated for ground contact but seem to last for 20 years or more(at least the older cca). Ground contact uses a higher percentage of chemical.
I also agree with Al. The treated southern yellow pine in the south is especially prone to warpage depending on the quality of the log it is sawn from. It's not as bad if you get a good slice of straight grained lumber near the center of the log. Treated lumber is delivered to the stores straight from the manufacturer and has not been dried. It is completely saturated and when exposed to the air dries in an unpredictable way sometimes with severe cups, twists and bows. Also if one side is wet and the other is exposed to drying in the sun it may cup or twist as well but then again a lot of wood will do that.
Bottom line is I personally think it's safe to use old cca lumber or most of the newer treatments for gardening.


Here is a link that might be useful: Wood treatments

    Bookmark   May 11, 2014 at 1:54PM
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