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Minimize effects of pressure treated wood on veggie garden

 
Posts: 3
Location: San Francisco, United States
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Hello,
We are foraying into the world of growing our own food!  But the instructions to avoid pressure treated wood were disregarded.  I suspect it was Treated with copper azole. It appears I can minimize the  risk to our vegetables by using an oil based product on the wood and lining with low-density polyethylene or high-density polyethylene) liner or a polypropylene fabric liner between the sealed treated wood and the garden soil.  
I’ve been trying to research food safe, oil based wood sealants and got overwhelmed.  Any suggestions would be welcome!  
Also, any suggestions on this topic in general would be much appreciated!
Thanks!!
 
pollinator
Posts: 287
Location: Yukon Territory, Canada. Zone 1a
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Hi Susan. Congrats on your new garden!

I have some questions:

Are you going for organic certification?
Are the posts already in the ground or can you prepare the holes to put them in?
Is it the brown or the green pressure treatment?
 
Susan Derm
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Location: San Francisco, United States
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Thanks, we are very excited (even our 4 year old has been talking about all the food he wants us to grow together )
The posts are already in the ground (I think at least 3 of them are in concrete since we also needed to add a small retaining wall adjacent.
We are not concerned about the organic label, just healthy food for us to eat (and share, if bounty allows).
The posts look reddish to me (purchased at Home Depot, I checked and they are definitely treated with copper azole).  Because we live in a big city, we also have a pressure treated fence against the other side of the bed which was installed about 3 years ago (light brown).
 
Chris Sturgeon
pollinator
Posts: 287
Location: Yukon Territory, Canada. Zone 1a
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When I was about that age my parents would play a 'name the vegetable' game; repeating the names or giving me clues by telling me the colour etc... to this day my Mom will turn to me and taunt "Say swiss Cha-ard." Evidently I would just absolutely refuse to say the name of this vegetable. Funny because steamed chard with butter is still one of my favourites. BTW I am a 42 year old man!

Anyway,
1) No cert is good because (in Canada) your property needs to have been treated wood free for 7 years to qualify. Now that may have changed with the newer treatments because...
2) The brown and reddish treatment (as opposed to the green stuff) doesn't contain arsenic. Just Copper compounds as you identified. Not dreadfully toxic, but not friendly to microbial or fungal life.
3)Unless you want to pull out the already installed posts, there's not a lot to be done. Maybe just don't plant anything but flowers or pollinator attractors right next to those posts.

If there are any posts yet to be installed, I'd create a soil break by filling the bottom of the hole with pea gravel and then packing the sides with angular gravel to anchor the post. Any tar, oil or plastic is both going to have it's own toxicity problems and cause the wood to rot out faster... so what's the point.

Even better, as some posters have mentioned in other threads, it to not use treated wood and char the below-grade portion; then endeavour to keep it's anchor dry. Unfortunately you weren't given that option.
 
gardener
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Susan,

You might consider a product called DryLoc that can be found at Home Depot.  It is actually a masonry sealer, but can make a barrier against the CCA in the wood.  I use it on my garden beds to protect the raised edges from the wine cap fungi in my woodchip based garden bedding.

Eric
 
Susan Derm
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Location: San Francisco, United States
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What lovely memories!!  Hope my son has some similar fond memories when he is in his 40’s!!
Thank you both for your suggestions!!  Greatly appreciated to have some guidance!!
 
pollinator
Posts: 378
Location: Canadian Prairies - Zone 3b
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Hmm. My understanding is that the copper-based product isn't a grave concern because it isn't taken up by the plant roots. It replaced the older arsenic-based heat treatment which the plants would absorb (yikes).

Natural wood will last a lot of years in a raised bed without any treatment at all. The posts embedded in the ground are vulnerable to rot, though using gravel to tamp them in may slow that down.

I'm seeing a lot of raised beds with a couple of layers of weed blocker fabric stapled to the inside. Apparently it alows the soil-facing wood to stay dry(er) to slow down decomposition. I suspect it would also provide a better drainage channel where any leaching would go straight down instead of into the grow zone.
 
Posts: 44
Location: 5b Ontario
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I, too, have raised beds out of treated wood. Seven beds and a giant planter. I didnt have any such info a few years back when we ordered a big pile of lumber to build them, and the older people I talked to all recommended the pressure treated instead of cedar because of cost.

I had some small concerns about gradual chemical leeching (I was concerned mostly about the dye coming out into the surrounding soil). Even though I didnt know exactly what I was dealing with,  I used thick layers of the landscaping fabric cloth that was cut, folded to double it, and stapled around the whole interior perimetre of the wood. Maybe the fabric has its own set of problems. Lol.

Three years later and I think, so far, so good. It might not be a perfect solution, but I am still convinced whatever I grow has far less chemical load than most conventional produce available at the store.

The boards themselves have no sign of rot or water damage, and the landscape fabric actually seems to help deter the voles from going right under. A few times they have dug along the bottom, but then they hit the cloth and stop. My cloth doesnt cover the whole bottom, just tucks underneath about 15 cm on all sides. Apparently just enough to fool the greedy little boogers. :)
 
Douglas Alpenstock
pollinator
Posts: 378
Location: Canadian Prairies - Zone 3b
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In hindsight, I would like to add that I am immensely respectful of growers who are trying to avoid getting caught in toxic traps. Asking questions, and running down hard data, is both thoughtful and wise.

It's been marathon planting season up here, with a 3-day rain rolling in. I confess that my posts have been quite terse, and perhaps not as nice and gentle and diplomatic as would fit the style of this forum.

Happy gardens, everyone.
 
pollinator
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Location: cool climate, Blue Mountains, Australia
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My answer is super simple: You will need the timber only if you are old and can't bend down. Otherwise, why would you use timber around a veggie garden? I don't have it and it is probably super annoying because the grass and other weeds are always growing through the timber where you can't get to it. Simply leave the timber out and keep it simple unless you do the beds around hip-high so that you don't have to bend down, this makes sense. people always talk about building a vegetable garden, but you grow a garden you don't build it!
 
Douglas Alpenstock
pollinator
Posts: 378
Location: Canadian Prairies - Zone 3b
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I think it depends on climate, soil quality, and topography. One size does not fit all.

At my old property, which was flat as a pancake, and situated on deep, black, natural soil, raised beds would have been a waste of time.

At my new property, on a steep sandy hill, terracing is the only way to get the results I want. It's a ton of grunt work. Some neighbours amend the subsoil and then truck in rich, black soil for the grow zone. But that's spendy, so they do it in raised beds.

Also, in a zone like ours with a short frost-free season, soil temperature is critical for germination. Raised beds are warmer, speeding growth; and also drier, requiring close monitoring.
 
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