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Wondering about your options in raised garden bed materials?
Wooden planters, built out of untreated wood raised bed garden materials, 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 your organic veggie garden.
It’s true. Treated wood for raised garden bed materials 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.
But, I’m skeptical about treated lumber for food growing planters.
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, these are roots. So, I just don’t trust that every plant will remain unaffected by a bunch of maybes in raised garden bed materials.
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. Or, better yet, I might select juniper for my raised garden bed materials. That’s because juniper boards are often made from invasive species trees. So, 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.
So, how long will those raised, untreated wooden planting beds last?
The photo shown here was taken in the summer of 2011. This board is one of many in a set of raised wooden veggie beds we had used intensively for over a decade before the photo. And, this board was the one to decompose the most first.
Unlike the other raised bed building materials in other parts of the garden, this example board 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).
This wood gave us over a decade of growing food year ’round before rotting.
Too, a nearby tree had invaded this bed and done damage to the board as well. Moreover, 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 brackets were important. That’s because we used them 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 a raised bed material made out of something treated would have lasted longer. But, once it did begin to rot, I wouldn’t be able to compost it.
Would a treated board leach toxins that may have made it into my food?
Maybe. And, again, I’m not into maybes when it comes to growing food in my raised beds.
Can cedar raised bed materials 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! In fact, years later, this entire raised bed eventually composted in place. That’s great! It fed the soil, which builds the environment for plant roots.
But, it took several years before this tired, hardworking piece of lumber stopped holding up all of that raised bed soil.
Can you teach me more about choosing wisely for my garden?
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Just curious how thick the cedar boards are that you used in the above article? I can’t locate any cedar thicker than 1 inch down here in the south eastern US.
LeeLee, As I recall, these boards were about 1.5″-2″ thick.
Gosh! Ok, so if I use 1 in thick cedar… it *might* only last 5 years? Bummer.
A lot of factors can impact how long a board will last. Good luck!
In Maine, some people use 2×12 wet hemlock (a type of pine). It’s heavier, since it hasn’t been dried, and it’s just rough cut, so you call a local mill and they deliver, for an extra $15-$20. Works great- my raised beds are 10 years old and still going, might get another 3-4 years. Cheaper than kiln-dried, especially if you get enough for multiple beds at once. We build them right over the grass-just cover the area plus maybe 12-18” around the bed with heavy, overlapped cardboard, add wood chips around the outside.
Thanks for sharing Liz!