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How Long Will Untreated Wooden Planters Last?

November 16, 2011
Hooped Raised Bed

Raised Wooden Beds are Ideal for Season-Extending Greenhouse Hoops

Wondering about your options in raised garden bed materials?

Wooden planters, built out of untreated wood, will probably last much longer than you think. Yes, untreated wood will decompose over time, but because it is untreated, you reduce the risk of potential toxins moving from your wooden beds into that organic veggie garden you’re starting to keep your family fed well.

Treated wood is controversial. There are plenty of articles and studies indicating that more modern methods of preparing wood to withstand ground contact has eliminated the potential for toxins to enter the soil from them. And, I’ve also read that should toxins leach into the soil, most plants won’t do anything with the toxins — implying that if the soil is toxic, the plants still won’t be affected and neither will the food we extract from them.

I’m skeptical. Plants do any number of chemical exchanges with their environment all the time. When they encounter chemicals they don’t know what to do with or they can’t expire into the atmosphere, they store it away. And a lot of stuff they store goes into the roots. And what’s a carrot or a beet or a potato? Yeah, a root. So, I just don’t trust that every plant will remain unaffected by a bunch of maybes.

I’m one to follow my gut instincts on these things, and my gut tells me to err on the side of caution. So, I prefer to spend a bit more money on untreated cedar (in the PacNW) for my edible garden raised wooden beds. In my estimation, the cost in those initial purchasing dollars is, to me, much less expensive than the potential health and environmental costs of taking another route.

Rotting Board

Cedar Board Rotting Over a Decade After Installation

So, how long will those raised, untreated cedar beds last?

The photo shown here (left) was taken this summer. This board is one of many in a set of raised cedar veggie beds we have used intensively for over a decade. This board was the one to decompose the most first. Unlike the others, it had soil and plant contact on three sides of the board — interior to the raised bed, on the ground below the bed, and opposite the raised bed where it was lined with ornamental Carex to edge a walkway (see photo at top of page).

That’s over a decade of growing food year ’round!

Too, a nearby tree had invaded this bed and done damage to the board as well. And, as you can see, we had compromised the integrity of the wood a bit more by affixing brackets on the exterior of the boards; these are used to slip in PVC for hoop houses. And, no, the PVC does not make ground contact on these beds.

Would a board treated for ground contact have lasted longer? Probably. And, I couldn’t compost it if it did begin to rot.

Would a treated board leach toxins that may have made it into my food? Maybe.

Can cedar leach toxins? Perhaps, but those naturally occurring toxins scare me a lot less than the man-made ones. Plus, given that cedar chips are in most composted mulch in these parts, odds are I’d have the same issue going on in my purchased amendments as well.

Can I recycle this rotting board? Sure; it’ll chop up great in the compost when the time comes.

For now, this tired, hardworking piece of lumber is still holding in that raised bed soil — if barely. So, I think I’ll try to eek out at least another winter with it before it is cut up and encouraged to rapidly return to the earth from which it originally came.

5 Comments

  1. Donna says:

    Our house had a series of railroad tie raised beds when we purchased it. And they are three to five ties high. When we bought the house, they held flowers only, but I like to grow produce. To replace them with untreated wood would have been a nightmare. I did some research and my solution was to dig out about 20″ of the soil, grind down the ties to good wood, tile the insides of the ties, lay down a couple layers of weedblock, a layer of gravel, then about 10 yards of Pacific topsoil Veggie mix. I tested my soil two years later and there were no toxins, so I feel pretty good about it (my first course of action if I had to do this again would be to have tested BEFORE all this . . . I just assumed the soil would have been bad, but the company I tested with said that most of the toxins leach out of treated wood pretty early in the process and the original soil may nt have been bad . . . my bad, should have thought to get actual data instead of guessing). I had also considered using bricks on the inside of the ties, but that was a bit expensive. I actually like the look of the bright colored tiles contrasting with the dark wood, so aesthetically it was a good choice too.

    When I took out my back lawn and built some terraced gardens (once again, mostly veggie), I used stone blocks.

  2. What about plain, off the shelf, pine 2×6′s? I built my son a 30 inch square “digging spot” (like a bottomless sandbox with soil and worms). How can I expect it to last?

  3. Shane, Thanks for writing in. How long your boxes will last can be influenced by a number of factors. What’s in them. What’s around them. How wet will they get. How active is your soil. Are they painted or treated. How were they built. And more. Odds are you’ll have them to enjoy for a few years, regardless. Have fun with them!

  4. Jason Ellis says:

    I put my cedar beds in a year ago and plan on expanding my garden with them. Yes, they’re a bit pricey but I think the beauty, peace of mind (non-toxic) and durability outweigh the extra cost. Thanks for the article. I hope mine last a decade as well :)

  5. Good for you Jason! Happy gardening!

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