What’s the bottom line on pressure treated lumber? Is it safe to use for vegetable gardening? I’m planning to build a few raised beds for growing vegetables this year and I don’t want to poison myself. (There are a few other people I’d like to poison, but that’s another story) I’ve read both “yes, it’s safe” and “no, the chemicals will leach out and contaminate the soil”. So, does anyone out there in StraightDopeLand have the definitive answer?
Organic Gardening did a series of rather scathing stories about pressure treated wood a few years ago, and they came down soundly against pressure treated wood because it tended to leech things like arsenic into the soil. The pressure treated wood industry shot back with their own studies which seemed to disprove OG’s claims, OG pointed out flaws in the wood industry’s studies, and the whole thing went back and forth until the Feds got involved and have ordered the pressure treated wood folks to find something better to use. Personally, I say that the OG folks were right, based on the articles they printed. (That doesn’t mean that they weren’t biased and overstated the risks of pressure treated wood, but I’d rather not take the chance.)
My brother built a new deck out of pressure treated lumber about 5 years ago. He commented to me last fall that the grass is starting to grow again under the deck, it had all died off shortly after the new deck went up.
Why take the chance???
It’s very easy to find another alternative.
I did hear that Home Depot will stop selling pressure treated wood very soon, ( this year or 04 )… and the new wood will be very expensive…
Which I think is very stupid… even if the wood did have minute traces of arsenic, it’s not going to hurt anything to have a deck built from it…
So if you’re in the market for a deck , I’d do it soooooon.
As usual they take something and go overboard with it…
Okay. So it looks like I’d better stay away from the pressure treated wood. So what’s my alternative? How about cedar? Is it sold without any chemical additives? I’m thinking it might be kind of expensive but if it’s safe I’ll have to go for it.
[Disclaimer] The following is based on US experience and I realize that preferred lumber species may vary according to region.]
As a contractor, I would recommend cedar. Pressure treated lumber (PT, we call it green plate) is on the way out, and I wouldn’t use it for a gardening project. Most PT is #3 pine (or equivalent), which, if you can find straight material to begin with, will always twist and bow and cup.
PT lumber is commonly made by immersing the wood in a copper/arsenic mixture (chromated copper arsenate), and pressurizing it to force the chemicals into the wood. These chems are not good.
The PT rating confuses a lot of people. Sure it is resistant to moisture, thats why it is mainly used as shoe plate on concrete slabs. It is excellent for this. However, why it got to be a deck/porch material/garden stuff, I don’t know (especially for 4x4 posts). PT is NOT as stable as most people think. If it has checks/cracks from the factory, it will get worse.
The best lumber cost-wise for outdoor projects is cedar or redwood. In my area, cedar is about twice as much as PT (for ex, a 4x4x8 foot PT post is about 5 bucks) and redwood of course a bit higher.
A tip: Whatever lumber you use in your garden, treat the ends of the boards with a sealant, Thompsons, Behr, or just roofing tar (non-toxic, of course :D) , anything that will seal the cut-off ends, this is where rot starts.
Okay, cedar it is! Thanks Klaatu.
I just read an article in the Globe and Mail about arsenic contamination in Canadian playgrounds, which came from the pressure treated lumber used. They found several times the federal limits of arsenic in the soil around the posts going into the ground in about 60% of the playgrounds they looked at. Can’t find the article online, but it’s from jan 22 2003 if anyone knows how to search that site.
nuthinboutnuthin, there’s no “ifs” about it, pressure treated wood does have a lot of arsenic in it, not just minute traces. This is the stuff that basically kills anything that tries to decompose the wood. And yes, if you know what’s in the wood and soil, then it’s not that big a deal… the problems start when someone else takes the deck out and builds their kids a sand box where the deck used to be and they start eating the dirt. Nobody takes soil samples on a 1-foot grid all over their yard and has a lab analyze for all known contaminants (at least before they get sick), so the less “stuff” you let leach into your ground the better. I don’t actually care about whether or not they still sell PT lumber… just pointing out there is some science behind the nervous opinions.
To make raised beds for gardening, you can always use cinder blocks. I’ve made beds up to 4 bricks high and they won’t tip over. These are also nice since there’s no cutting involved and you can change the layout whenever you want. Though on preview it looks like you’ve already found an alternative…
Blooming 'eck! I’m currently renovating our small garden, and was planning to use pressure treated wood for the borders. This is a very important heads up, especially in having two very young children I wanted to make the garden safe for.
I have an untreated, redwood 4X4 post for my mailbox that has now been in the ground for 22 years with no sign of rot.
I work at Ace Hardware and deal with this lumber everyday. It’s true that pressure treated lumber containing arsenic will not be sold anymore before long. (I’m not sure of the date) However a new kind of pressure treated lumber will be availible. If you want to go top of the line with no maintinence you should look into a new product we’re selling called EON. It’s 100% synthetic wood. It’s basically like trex only doesn’t contain any wood. (Trex was 50/50 plastic/wood) EON has a liftime warentee and it maintenence free. There’s my sales pitch…
In my opinion cedar would work fine too, or even white oak because it’s very hard and dense and resists weathering.
On a related note, I just had a dock built and the contractor used “ironwood.” He gave me a 25 year warranty on the material, but I’m still wondering about it. Does anybody have any experience with this stuff?
I sort of do. I’ve made small things with it, and we considered replacing the rails that hold up our banister with it. It deserves its name; the stuff is really hard. Easy enough to work with, except for the bit about dulling blades pretty quickly. The sawdust smells like coco-puffs, which I realize isn’t all that helpful, but I found it amusing. It is a good choice for a deck - pretty, strong, and long lasting. It is dense, at 67 lbs/cubic foot, compared to 39-47 for maple. I seem to recall reading that it is rot resistent, but my most available books don’t list its properties. It is considered a somewhat exotic wood here (Los Angeles), but it might more readily available where you are. Frankly, it is an exceptionally nice thing with which to build a dock.
So what is going to replace the CCA lumber?
I prefer redwood, it doesn’t smell as much as cedar does.
black locust is another poss., if it’s avail. in your area.
Cedar will rot!
I had cedar 4 x 4 post to rot below grade in 15 years… in dry west Texas.
Redwood will not.
Redwood is used in cooling towers I have seen cooling towers that have been in service for 50 years with no rot.
My deck is treated lumber.
No grass grows under it for grass doesn’t grow in the shade.
My boat dock is treated lumber. It’s over 12 years old and in excellent condition… cedar would have roted years ago.
I don’t fear treated lumber but I don’t eat off it either. Just use common sense and there is no problem. 
If you live where termites are an issues, do not bother with cedar, it will be gone in a couple of years if it is in contact with the ground. My raised bed garden in Houston is lined with CCA treated wood. Basically in Houston you can:
- replace the wood every two years.
- use cca.
- use cement/masonry.
That would surprise me. While it is true that the production CCA treated lumber is expected to cease in the near future, there will still be a supply of 4+ years on hand to be sold off. Can’t imagine HD missing out on a few extra $ from the stuff.
On a side note…
I did an editorial photo shoot at a CCA lumber treating plant a couple of years ago. What a shady business that is (guess I can’t blame 'em given all the bad press they get). I drove over 4 hours to get there and the plant owner gave me a 10 minute tour during which I was supposed to get all the shots I needed. He kept looking all around for what I assumed was something he did not want me to photograph. He had to look through the camera every time I got ready to shoot, and shuffled me out of there as fast as he could.
From what I understand from that experience, the industry line on the whole thing is…arsenic is a naturally occuring chemical. You could go out in the forest and take a soil sample and find a higher concentration of arsenic than a sample take in close proximity to a structure made of CCA treated lumber. Don’t know if I believe that, but I didn’t want to get the Jonestown treatment on the way out so I just nodded and kept repeating “fascinating, truly fascinating…”
olefin, redwood can rot, I have some on the yard. What happens is termites get to it. Yes, there is a termite that eats redwood. Guess what? Yep, I have those.