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Treated Wood and Raised Bed Garden

Jordan Pogorzelski

6 years ago

Hi There,

I have some left over treated wood from an old deck of mine and I'm looking to put it to use and construct a raised bed garden. I have read that treated wood is not ideal due to its potentially toxic properties. Could I simply line the walls with a plastic material to prevent this? Or does plastic have some leachable toxic properties as well? If someone could please suggest a plastic liner to use I would be very grateful,

Best,

Jordan

Featured Answer

Jean

6 years ago

How old is old? Neither the old stuff (arsenic treated; widely feared) or the new stuff (copper treated; safe) leach enough into the soil to be a problem.

In the olden days, people lined the beds with plastic. Not supposed to leach. But some folks fear it anyway.

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Comments (6)

NHBabs z4b-5a NH
6 years ago
I would choose not to use old treated lumber on a veggie bed since while it may not leach when new, if it is old and has been exposed to the weather a while along with now damp soil or plastic, it will start breaking down eventually. You can try lining with plastic, but any plastic sheeting that has light exposure will start breaking down in the UV of sunlight, leaving you with lots of tiny plastic fragments. Is there a reason not to plant in the ground? Or use a material that isn't inclined to break down over time for the bed walls?
Jordan Pogorzelski thanked NHBabs z4b-5a NH
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When I built my current framed beds 20 years ago, I used PT lumber. At the time, it seemed like the best idea since sliced bread. But after 20 years, I have to wonder just how much is left that can leach into the soil. And the newer ways of treating wood do seem to be a lot less potentially harmful that the old arsenic compounds. So I am a bit conflicted about what to say now. After thinking on it for a while, I would say that I sure wouldn't re-use any of the old PT wood to make new frames, probably wouldn't buy new PT wood, and plan to replace my existing frames (and the soil within) with either artificial wood or cinder blocks (and new soil). The artificial wood is not cheap and isn't terribly strong either (thinking of how often I put pressure on the frames while turning the soil to add compost). I think I'll redo my deck tops with it (adding more joists), but use cinder blocks to replace the old PT wood garden bed frames. And I kind of like the idea of having the holes in the tops of the cinder blocks to plant flowers in all around the edge... I'll have to learn about cementing the blocks together though (an undiscovered subject for me at the moment). On the other hand, if I had some reason to use PT wood (like having a bunch on hand or a cost consideration), I would line the bed with pond liner (best) or black plastic (OK). That would have to minimize any leaching, I think.
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Jordan Pogorzelski
Original Author
6 years ago
Thanks for the replies,

The deck is probably around 10-15 years old, I doubt it's arsenic treated but I'm not sure as I wasn't around for the installation/purchasing process for the deck.

I'll be trying both a raised bed and a regular garden bed this year. My girlfriend is hellbent on building a raised bed so it is what it is. I saw the old deck wood as a great opportunity for reuse (I was planning on building a pier from it originally). I may try lining with a plastic, but not sure which "type" of plastic to use. I'd be sure to cover all plastic with soil to avoid UV exposure/breaking down.
susanzone5 (NY)
6 years ago
Forget the treated wood and plastic. You have the opportunity to grow food without chemicals. Why would you want to risk poisoning yourself?

You can make raised beds with just soil. Pile it up. I put cedar mulch between the "beds." That keeps the soil in place. You can line the edges with rocks or get some cedar wood boards. Cedar wood takes a long time to decompose. No need for plastic. Just dump the soil onto the ground. It will be better for draining anyway.

Just my opinion and my experience.
Jean
6 years ago
At that age, it's copper treated. Safe to grow veggies in spite of the hype you hear & read.
susanzone5 (NY)
6 years ago
Treated wood is not made under food regulations. Chemicals other than copper can be used in manufacture. Just sayin'.

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