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]

Garden beds 2013 002.JPGThese 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.

[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...

[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.

[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.

[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.

[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.

[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

[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.