Ask a Question forum: Raised Garden Beds Where Treated Lumber Had Been

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Jun 11, 2016 1:38 PM CST

We had a square made of four large 8' pieces of treated lumber in our backyard that was then filled with pea gravel as a base for a hot tub in our back yard. We got rid of the hot tub and I wanted to dig out the large frame of wood to put a garden bed inside the area where it had been. It had been there for about 20 years, so the pea gravel is mixed in with quite a bit of dirt. I was going to dig down to where there was no more pea gravel and only dirt and put a raised garden bed in there (I was planning on having it 4' x 8' and I was not going to put a liner in the raised bed). My question is whether or not this was safe putting the garden bed where the treated lumber had been for so long?

Name: Thomas
Deep East Texas (Zone 8a)
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Jun 11, 2016 2:34 PM CST
I do not think you have anything to be worried about. The age of the lumber means it would have lost most of the chemicals by now and the earth mixed with normal rain would have leached out most of the remaining residue. If you plan to add any new top soil that will also help.

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Name: Jean
Prairieville, LA (Zone 9a)
Charter ATP Member Plant Identifier The WITWIT Badge Garden Sages Celebrating Gardening: 2015
Jun 11, 2016 2:43 PM CST
Hi @grmil1 welcome to NGA

Here is some info for you. PT lumber after 1993 was treated with a less hazardous chemical.
Name: Evan
Pioneer Valley south, MA, USA (Zone 6a)
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Jun 11, 2016 2:53 PM CST

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Per the PSU site it was phased out in 2003. If you choose to you can always have a soil sample tested at your county extension or equivalent. The test for arsenic at the UMass extension takes 2-4 weeks.
Name: Jay
Nederland, Texas (Zone 9a)
Region: Texas Region: Gulf Coast Charter ATP Member I helped beta test the first seed swap I helped plan and beta test the plant database. I was one of the first 300 contributors to the plant database!
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Jun 11, 2016 3:05 PM CST
Just my opinion, but I would say you have nothing to worry about. As Thomas said, with the age of the wood, any toxins would most likely be gone by now. I read a study years ago about test being done on treated wood and any leaching was limited to the immediate contact point with the ground and the plant uptake of the toxins was extremely minuscule. I believe you take in more harmful chemicals with every breath you take than you would ever get from treated wood.

Name: Dave
Southern wisconsin (Zone 5b)
Region: Wisconsin Lilies Dog Lover Garden Photography Daylilies
Jun 11, 2016 3:17 PM CST
Along with what everyone else has said. Being that old the elements have probably taken out any chemicals left in the wood. Especially UV exposure and rain. And it would probably only really be a concern if you were planting things you planned on eating what you grew in the bed. If grass and other vegetative things can grow there now, I'm sure you will be fine.
Name: Jean
Prairieville, LA (Zone 9a)
Charter ATP Member Plant Identifier The WITWIT Badge Garden Sages Celebrating Gardening: 2015
Jun 11, 2016 3:21 PM CST
And if it was treated by a later than 1993 chemical, (non-CCA chromated copper arsenate) it was tested and proven that any leaching into the soil would have minimal effect on plants and would be such a small amount that it would have no more effect on humans or animals than most things we come into contact with on a daily basis.
[Last edited by Moonhowl - Jun 12, 2016 9:39 AM (+)]
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Name: Cindy
Hobart, IN zone 5
aka CindyMzone5
Celebrating Gardening: 2015 Plant Identifier
Jun 12, 2016 9:30 AM CST
A simple suggestion to allay any doubt. If you're putting in a raised bed with added compost, black dirt, etc., you could lay down cardboard before filling the raised bed.

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