Trex for raised bed gardening?

[Eric DeSilva]

I'd like to build some raised beds for a vegetable garden this spring. In an ideal world, my local BORG would sell nice, dimensional redwood and I could bung them together out of 4x4s and 2x6s like everyone else. Unfortunately, my local BORG doesn't stock dimensional redwood. I don't want to use PT lumber, because I'm worried the various nasty chemicals and salts could leech into the soil and I plan on eating what comes out of the garden. That started me thinking about Trex. Plastic seems inert, and it is meant to be outside. Anyone see a downside in using it for raised beds? I know it is kind of flexy, so I'd need to put in a lot of supports to keep it from bulging... So they make some kind of 4x4 equivalent for Trex?

[Mark Bolton]

Your right in the conclusion that you cant use the trex for anything structural. Often times they spec' that your not even allowed any overhang on a step. They want you to wrap deck edges and steps with 100% support. We do it anyway because it looks better.

While Ive never done it, I think the amount of support you would have to put in to ever have composite decking not bow/bulge would make using the material cost prohibitive. And as you say there isnt really much option with regards to support members other than PT, Cedar, Redwood, etc..

I think the general consensus in the gardening world is to simply use untreated lumber and plan on getting 2-3 seasons out of it. Not a great option.

Hope someone else has a better solution. Masonry?

[David Helm]

259119These beds are made from 2 X 12 Doug Fir. They have been in place for 8 years. Yes there is a little rot, but not much. Untreated wood can last much longer than people think. Since these are not joists supporting a floor, a little rot isn't a big deal.

[Joe Angrisani]

....I think the general consensus in the gardening world is to simply use untreated lumber and plan on getting 2-3 seasons out of it. Not a great option.....

I made my raised beds out of regular lumber, but then dug down a few extra inches on the inside. I hung heavy black plastic sheeting on the inside walls (open at bottom underground). The lumber stayed dry on the outside of the barrier, and bugs and ants did NOT move into what would otherwise be underground wood. Ten years, plus....the wood and plastic held up....easy.

[Kevin Bourque]

What about concrete building blocks? You lay them where you want and then fill them with dirt to hold them in place.

[Mel Fulks]

The radio gardener show guy I listen to says there is no evidence that pt lumber has any effect on the food plants. There are some who will not use it ,but I disagree that there is a consensus against it.

[Harold Burrell]

What about concrete building blocks? You lay them where you want and then fill them with dirt to hold them in place.

That's what I am planning on doing this year.

Of course...we don't talk about concrete blocks here...

[Bill Holland]

New PT lumber is safe for food plants, back 20 years ago they had arsenic in PT lumber that could leach into ground & be absorbed by plants. they are now banned from using it in lumber. I have had a 4' x 8' raised beds for 6 years not rot. I used 5/4 boards for sides & ripped some 2x4's into 2x2 squares for each corner & add 1 each about 4' down the sides. Works like a champ. Raised beds make weeding such an easy task not being bent over or on your knee's to handle them.

Bill

[Brian Elfert]

I bought some landscape timbers made of recycled plastic about five years ago. Essentially they grind up old car interiors and made the timbers out of the ground up material. There are lots of pieces of fabric, hard plastic, and some metal in the timbers. They are mostly a dark grey with speckles throughout from the other materials. Structurally, they aren't as strong as wood. They will get soft and bow or bend if they sit out in the hot sun before being installed. I don't know if the store still sells them or not.

My parents are on their second or third set of green treated timbers in 30 years around some flower beds. The ones there now could use replacement in places due to rot.

[Chris Damm]

My raised beds are built out of red cedar. They have held up well for the last 5 years. They are 3' off the ground which makes for easy back saving gardening!

[Curt Harms]

I don't know about cost and it isn't easy to find but I'd consider black locust. Stuff has been used for fence posts and is reputed to last just short of forever.

[Eric DeSilva]

Thanks for all the replies. My inclination at this point is to think about just using standard dimensional lumber--I like the idea of lining it to avoid premature rot. Cedar and redwood seem unavailable at a reasonable cost, cement blocks too industrial, and I still don't trust PT lumber around food.

[Greg R Bradley]

PT lumber is all poisonous. The newer PT may not be as bad as the older PT that used arsenic. It could be worse! Just read the recommendations for handling, sawing, etc. and it should scare you badly.

Many plastics are harmful when new. Some become harmful as they break down. Most of the plastic lumber like Trex is made with recycled material so it could have other items that are harmful.

There are organic gardening websites that will give you more information. Also, if you are not going to make your own growing media, you need to be careful what you buy as most contains chicken manure, which has arsenic in it.

[Jason Roehl]

Warning labels about chemical dangers have become almost meaningless. Due to fear of litigation, everything gets a warning label (and is "known to the State of California to cause cancer"), whether it's dangerous or not.

And that doesn't even address whether or not plants will take up the unwanted chemicals out of the soil.

[Rick Potter]

It was cheaper for me to use cement block than Trex. Lifetime warranty against rotting or flexing:rolleyes:

Rick Potter

[Lee Schierer]

I made my raised beds out of regular lumber, but then dug down a few extra inches on the inside. I hung heavy black plastic sheeting on the inside walls (open at bottom underground). The lumber stayed dry on the outside of the barrier, and bugs and ants did NOT move into what would otherwise be underground wood. Ten years, plus....the wood and plastic held up....easy.

What about using that dimpled plastic that is is used against a foundation to allow water to drain to the weeper tile at the base of the wall. Lining your raised bed with that with the dimples toward the wood would allow the wood to dry, which would considerably slow the rotting process.

[Tom Fischer]

I don't know about cost and it isn't easy to find but I'd consider black locust. Stuff has been used for fence posts and is reputed to last just short of forever.

That's true about black locust (40 - 75 years in the ground). But it is not so easy to buy quantities of it.
Oak (red or white) lasts a long time too (~15 years?). And easy to buy.
All woods last longer if you put some stain sealer on them.

[Kent A Bathurst]

PT lumber is all poisonous. The newer PT may not be as bad as the older PT that used arsenic. It could be worse! Just read the recommendations for handling, sawing, etc. and it should scare you badly.

Simply put, Glen, these comments are opinion, not facts, in practical, real-life use.

You should wear a dust mask. Same for redwood. You should not eat it. Same for plywood or OSB. You should not burn it. Same for plywood or OSB. Other than that, it is perfectly safe to use. This includes usage in gardens, but many people prefer not to do that. Certainly a legitimate choice, but not one backed by cold, sober, science.

In fact, the older, traditional treatment - CCA [chromated copper arsenic] disappeared from most retail stores [but not all] because of a classic tale of headline-driven emotion, marketplace maneuvering, and government bureaucratic inaction.

When the big hue-and-cry about the arsenic content was sweeping the nation some years back, everyone was in a big rush to judgement. It turns out that the chemicals in this process, like many, many others in other applications, must be reauthorized every 5 years by the EPA. That 5-year window was approaching. The big box fellers were stuck between a rock and a hard place. If they did not switch chemicals, they would risk being punished by the public because of the publicity. If one box switched to the higher-cost alternatives, they would risk being punished by the public, due to price differences in the store.

The elegant solution for everyone was for the EPA simply to not renew approval. This is not the same as ordering the product off the market. Voila! CCA is no longer approved, and everyone's costs and prices rose in unison.

As the emotional headlines faded away, the grinding scientific studies continued, and were eventually concluded. The result? CCA was perfectly safe.

Which helps explain the fact that you can, indeed, still buy CCA-treated lumber. Not at the big boxes, but at locations serving markets other than the DIYers. It was, and is, the single-best, cheapest, treating system for all applications. It is still approved for use in agricultural applications. It is still approved for use in wood foundations for residential housing. It is still approved for treating plywood. It is still approved for submersed applications [docks, seawalls, etc.] The alternate chemicals simply do not perform in those situations.

Cattle licking and chewing on CCA posts. Any home with PT plywood sheathing. CCA pilings sunk into the waters of our fisheries - I catch fish off the CCA dock of a friend's house in the Lower Potomac section of the Chesapeake Bay estuary, and eat 'em if they are big enough and dumb enough to hook themselves on my line. Vegetables from raised beds framed by PT lumber - even CCA. None of these scare me. None of these are hazardous to my helath.

Wear a dust mask. Don't eat it. Don't burn it. Not exactly the same as a toxic superfund site.

Facts are stubborn things.

[Peter J Lee]

There is a lot of arsenic in CCA. It readily leaches out and takes a long time to break down. Chrome is an additional issue.

CCA was reregistered without any epa evaluation and specifically did not address use in agriculture.

[Ted Calver]

If you have the space, it's not necessary to box in your raised beds. All mine are raised 8"-12" and when I form the beds with the Mantis, I just use my foot to compact the soil at the edge and then mulch the sides and the path in between with bark fines.
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The raised beds get hooped with EMT and covered by Agribon fabric. The fabric lets in light and water and keeps the bugs out.
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[Frank Drew]

As the emotional headlines faded away, the grinding scientific studies continued, and were eventually concluded. The result? CCA was perfectly safe.

Citations, please; everything I've read indicates that under certain climate and soil conditions (sunlight, rain, acidic soil, etc.), Copper, Chromium and Arsenic can leach from CCA treated lumber; can migrate a short distance through the soil (some inches, not millimeters) from the lumber; and that some plants can take up those metals, with arsenic uptake the most likely (great, since that's the one most worrisome to human health). Also, from the studies and summaries that I've read, the potential human ingestion of, say, arsenic, from plants grown in soil close to CCA timbers is probably within the safe level, but to be safe either use another material for your raised beds or isolate the PT lumber with plastic or some other barrier.


None of these [uses of CCA] scare me. None of these are hazardous to my health.

There's no demonstrable connection between those two sentences.


Facts are stubborn things. Indeed, but you haven't provided any. Again, if you can point us to any studies that show, conclusively, that there's no long term risk involved in using CCA PT lumber in raised vegetable beds, please post some links. Your personal risk tolerance isn't evidence of no risk.

[Kent A Bathurst]

There is a lot of arsenic in CCA. It readily leaches out and takes a long time to break down. Chrome is an additional issue.

CCA was reregistered without any epa evaluation and specifically did not address use in agriculture.

First:

You may rest assured that posts and poles, for use in agriculture [fences, pole barns, etc], and pilings for use in submersion [docks, seawalls, etc] are treated with CCA. The alternatives don't work nearly as well, and are much more costly in their failed attempt.

Next:

" After considering the riskassessments, available information aboutalternatives to chromated arsenicals for specific uses, publiccomments, and risk mitigation options, the Agency developed its reregistration eligibility and risk management decisions for wood preservative uses of chromated arsenicals.As a result of this review, EPA hasdetermined that currently registered uses of chromated arsenicals are eligible fo rreregistration, provided that the prescribed risk mitigation measures are adopted and labels are amended accordingly, and required data are submitted."

Excerpted from from the EPA: http://www.epa.gov/oppsrrd1/reregistration/REDs/cca_red.pdf


Also, from the studies and summaries that I've read, the potential human ingestion of, say, arsenic, from plants grown in soil close to CCA timbers is probably within the safe level....

You're making my argument for me.

[Frank Drew]

You'll note the word "probably" -- that's a rather slender reed on which to hang your and your family's wellbeing.

[Kent A Bathurst]

You'll note the word "probably" -- that's a rather slender reed on which to hang your and your family's wellbeing.

Your word, Frank. Not mine. The EPA does not equivocate. Nor, sir, do I.

I do not advocate that anyone should use any material for any purpose unless they deem it suitable, in their opinion, for that purpose. I simply brought history, facts, and science into this discussion. Nothing more. Nothing less.