This is a directed question about building a terraced retaining walls around a garden. I want to build a vegetable garden into a small slope (about 3′ rise). I like the look and convenience of treated lumber, but cannot use it because of the chemicals leaching into the soil where we are growing food. Stone is too labor intensive, so that leaves modular block, which is more involved than I wanted and too solid looking.
Does anyone know of anything like the treated lumber that would not risk poisoning a garden?
Replies
White Oak logs, Walnut logs, Cedar, Locust. Almost any of these can be had depending on where you live. ( I didn't check your profile yet for that INFO.)
Sawmills that saw "cants" or RR ties, have some that may be White oak,,these are great, if had before creosoting.
I 've used OLD, really old creosoted ties, with no harm. But I can't suggest you do the same.
I will not in ANY way, use ACQ, or CCA treated in my garden, but for some reason, old creosote is less of a concern for me.
EDIT: Welcome, I see it is your first post..filling out the profile offerd on the upper right of this screen ( or click on YOUR name, in this address to you), will tell us more pertinant info. esp. Location, to assist in your future needs.
Edited 6/28/2007 2:53 pm ET by Sphere
I'm upstate New York (forgot the profile). I could check one of the local mills for 6x6 oak. I like the look of horizontal timbers, and if I can afford the hardwood, that'd be fine. But wonder at the lifetime of untreated hardwood partially burried in soil, even though with the usual drainage. Also, we have a carpenter ant problem. But if I could get 15 years out of it, that would do for me.
I was ouiginall thinking of some version of manufactured deck material. but couldn't find any in a 6x6.
Well, my home is 150+ years old, logs..of White oak, and chestnut, and some are still sound, ven being partially buried.
White oak is your best bet up there, it'll give ya plenty of life, even the ants aren't crazy about it..too much tannin.
What Sphere said.white oak is used for sill beams in old log homes. ( pay attention - not red oak, white oak - worlds of difference
Locust is used for fence postsI have white cedar garden structures ten years old just starting to go by and lots of carp ants
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anything like the treated lumber
What sort of "design" are you thinking of, here?
"Pallisade" of vertical posts; posts and horizontal planks on edge; big "sleeper" timbers?
I ask, since you could just go get untreated western red cedar, or cypress, or whatever is a naturally rot-resistant wood in your region (hint, hint: Fill in your Profile, and "we" can guess better, if we know, generally, where you are).
Now, since the lumber is untreated, eventually it will need repacing, which may help define the "how" of the bed. As a guess, using stout posts vertically to define the corners, and likely the middles of the "runs" of the bed, you could then set planks against those posts, and let the back fill hold them in place. I might line the bed with landscaping fabric, to make later work the tiniest bit eaiser, too.
Oh, and Welcome to BT!
I like horizontal instead of vertical. But as u say, working with untreated wood, then use a design that make replacement easier, makes sense. Your idea sound like what they do to hold banks on the shore. Even though I'm not dealing with much rise, I'd have to connect the virticals to deadmen with tiebacks to keep them up straight.
I'd have to connect the virticals to deadmen with tiebacks to keep them up straight.
Well, I was kind of thinking a 50/50 on the posts, as deep down as proud "up," which ought to keep them midddling straight. If you found a source for some 4x6, you could set the "long" dimension out to help buttress the sides. You'd get a nice spot to set a flat perimeter plank around the bed edges this way, too.
If this is going to be like some of the vegetable garden plots I know, there will be a goodly amount of working the soil fill and such--so it's not the always damp contact with clay soils that will come after the wood. You might consider putting in a narrow gravel path around the bed to give you some drainage (and a place to bring the inevitable wheelbarrow). Better drainage on the outside might "buy" you a bit more longevity in the materials.
Lastly, I'd think about doweling the planks to the posts, if only to skip having metal fasteners oxidizing away next to the butter-sugar corn. Oh, and I'm using "plank" with some consideration here, 4 2x10 will get you your 36" height neatly, and have plenty of "oomph" to hold up three feet of soil while supported only every 6-8' or so.Occupational hazard of my occupation not being around (sorry Bubba)
You might be able to use pt timbers with plastic/impermeable sheeting on the fill side. If it's a true retaining wall (versus timbers simply laying on an existing slope) some kind of deadman/periodic support will be necessary to counteract the force of the dirt.