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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.

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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.

28 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!

  6. tom little says:

    should I use western red cedar for raised beds?

  7. Tom, Cedar is certainly an option.

  8. greenhorn with a greenthumb :) says:

    i have gardened for years with vegetables, but i wouldn’t consider myself a “serious” gardener…but i LOVE it! i always have something going, but not always veggies… anyway, i would like to change that & try some raised beds so i can have a garden year round. i do live in FL, so it’s pretty much always hot. . . what joy. :/ so, i’m debating 2 inch untreated pine, or cedar, which is only 1 inch thick. i read that 2 inch thick should last a decade, but i’m skeptical. i will have tomatoes, beets, radishes, okra, peppers, carrots…just about anything i can i guess. so it will be watering on a pretty consistant basis. so, after all that babbling i guess my question is…which one would last longer? 2 inch pine, or 1 inch cedar? thank you for any help! i’m chomping at the bit to finish this this weekend. all my seed sprouts are screaming for leg room!

  9. Greenhorn, There is a lot of variation in the grade of materials as well as the tree source of materials. Thicker will likely last longer, but the material grade may play into that as well. Plus, thin, long boards can be flimsy. Good luck!

  10. greenhorn with a greenthumb :) says:

    i went with 2×10 boards… we shall see how this works. thanks for your comment. i never even thought about the thin boards getting flimsy, especially with 4×6 beds. a lot of dirt. now i’m just looking for a good central florida gardening magazine, or book. off to do more research. 🙂 happy gardening!

  11. Good luck Greenhorn with a green thumb!

  12. tim says:

    You could treat it with tung oil or paint it with milk paint and still compost it. These would add some life but not as much as pressure treating.

  13. Thanks for your comment Tim. Have you used Tung oil for raised beds? Seems there may be thinners required that might add toxicity. Too, doesn’t it scratch fairly easily, exposing points for rot beneath the sealed surface? Just curious for more details. Thanks!

  14. Bruce Fein says:

    I made a raised bed on stilts. I laid 5/8 inch cedar fence boards as the floor w 1/2 inch gaps between. I can place 12 inches of top soil directly on them or line with plastic and cut slits between the boards for drainage.
    I was told, I’d be lucky to get 2 years out of the boards if left unlined w/o plastic. Any recommendations?

  15. Bruce, first, not sure why you chose to create a floor for raised beds. Are you trying to keep your plant roots from growing into the earth below? Odds are those roots will find their way in. Lining with plastic may sound like it will preserve the wood, but in our experience it doesn’t really do that. Moisture, soil, insects, roots, etc… can get between the plastic and the wood, and rot may speed up in a “trapped” environment like this. Wood won’t last forever. How long each type of wood will last will vary with location, use, grade of wood and so forth. Planning to compost the (untreated) boards when they break down may be a realistic plan to make. Good luck!

  16. GottaHaveFreshVeggies says:

    So, given all those comments, what would be a plan of action for someone who doesn’t want to use pressure treated or any other chemical products, and wants to build planter boxes? Are there 2 or 3 options, perhaps considering price range?

  17. There are lots of options, and they may vary by location. Cedar, which is mentioned in the article, is often available. Pine too. And, there any number of other woods, all of which may be available in varying grades, which may impact how long the boxes will last and how much the materials will cost. Visiting your local lumberyard is a great place to start for pricing and options.

  18. Mary Ann Perruzzi says:

    I want a “V” shaped raised garden bed approximately 6 18’x 2’ raised beds. I have been looking at composite decking which expensive $2.70 an linear foot I was thinking of IB PVC roofing which is $4 a square foot. What are your thoughts about cedar raised beds compare with the composite decking and IB PVC roofing in years lasting and cost? How about putting weed control woven fabric in between the compost and the raised bed material for drainage? Thank you

  19. Mary Ann, None of this sounds like something we’d suggest. Going natural is more our style. Petroleum/plastics are not. And, as for landscape fabric, consider this: http://gardenmentors.com/garden-help/gardening-guidelines/why-landscape-fabric-weed-barrier-wasteful/. Good luck!

  20. steve says:

    I just found this thread…after building 4 raised beds out of 2×6″ pine. Someone suggested I char the wood (bottom and interior) with a torch…to add some protection (?) to the wood. Any thoughts on this method?
    Thanks!

  21. Joe says:

    Will charing the wood (inside and on bottom) help reduce the wood from rotting?

  22. Steve & Joe, We don’t have experience charring wood to reduce rotting. If you try it, let us know how it goes! Good luck 🙂

  23. Brian Mountain says:

    I understand that there are variables, but how long could I expect PT lumbar to last in a raised garden bed, especially if I water sealed it prior to adding dirt?

  24. Brian, We don’t tend to use pressure treated lumber in raised (food) gardens. And, we also avoid using sealants on wood. While these may seem safe to some, for us, erring on the side of caution is the direction we prefer to take. Certainly, you could talk with your material vendors to get their inputs, and perhaps studies, on the materials you’re considering. Good luck!

  25. Lee says:

    Needed some advise – considering 2 options:
    Garden blocks (https://www.homedepot.com/p/Oldcastle-7-5-in-x-7-5-in-x-5-5-in-Tan-Brown-Planter-Wall-Block-16202336/206501693) with 2x6s – cedar is too expensive. Would untreated pine be worth it? Or would it rot too fast?
    or
    Retaining wall material (https://www.homedepot.com/p/Pavestone-RockWall-Small-4-in-x-11-75-in-x-6-75-in-Yukon-Concrete-Retaining-Wall-Block-87550/204643744) – would these leach toxins anyway?

  26. Lee, thanks for writing in. You’ll need to check with the manufacturers of specific materials for your individual needs. Best of luck!

  27. Barbara Finlay says:

    I bought an old wornout dresser with some good wood drawers. I want to use these as planters. I have drilled holes for drainage. They are old enough that even the bottoms are wood, unfinished. I am hoping these last a while, because they make nice ready-made planters for my herbs.

  28. Barbara, Thanks for sharing. One of our client repurposed old drawers as planters, and it turned out beautifully. Keep in mind, that an old dresser may have finish/paint/glues that aren’t ideal for food growing situations. You may want to consider using the drawers for ornamental rather than edible plantings. Good luck!

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