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Shou Sugi Ban for raised garden bed?  RSS feed

 
Amanda Robinson
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I want to build a terraced garden up a steep slope on my land.  I have built raised beds before and just used untreated planks screwed together knowin that after a few seasons I would need to replace them.  Not a problem since the rotted wood could be incorporated into the graden.  For my current project I do not want to have to rebuild every few years as I will likely néed to include stairs and standing platforms between each level.
I was watching Fixer Upper on home and garden TV and they showed the Shou Sugi Ban technique on wood panelling for a house boat.  Does any one know if this would be viable in a garden?  I believe it would be non toxic.  This would be a garden used for vegetables, fruits, and herbs.
 
Andrew Brock
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If using cedar it would absolutely work. I've used it on Doug fir that is outside and it seems to help. What are your specific concerns?
 
Steven Kovacs
Posts: 221
Location: Western Massachusetts (USDA zone 5a, heating zone 5, 40"+)
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Are you set on using wood, or are you open to other materials?  If you have access to rock, brick, or "urbanite" (used concrete chunks), and the time to install them, they should last indefinitely.
 
Marco Banks
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Location: Los Angeles, CA
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books chicken food preservation forest garden hugelkultur trees urban woodworking
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Yes, it would work, and yes, it would inhibit decomposition of your boards for a much longer time period than un-charred wood.

Drawbacks: 

1.  It's time and fuel consuming to do.  If you use some sort of torch/flaming device, it'll take you a long time to evenly char the entire surface of every board.

2.  You'll need to carefully char the boards so-as to not weaken the structural integrity of the wood.  Too long over the fire and it will burn too deeply into the body of the board, not just char the suface.  Shou Sugi Ban boards are normally used decoratively and for things like siding where structural integrity isn't critical.  If the fire burns into the wood too deeply, it actually creates pathways for fungi and bacteria to enter the deeper unburned tissue of the board.  Once the burn has "alligotor'ed" the wood, it's gone too far.

3.  You'll need to char the end-grain of the wood, as this is where moisture most naturally wicks into a board.  That may make it difficult to nail without getting tear-out or splitting.

Yes, it would inhibit rot, but it's not a perfect long-term solution.  Bio-char is wood that is completely charred all the way through.  Pyrolysis penetrates the deepest parts of the wood tissue and changes it to be highly resistant to further decomposition. 
Shou Sugi Ban is just a surface treatment, so the interior board will eventually rot.
 
Amanda Robinson
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I appreciate all of the responses.  The project I have in mind is pretty large so maybe this idea will consume to much fuel and time.  I have made the decision to do a small bed and see what happens.

As far as commitment to materials I am open to anything non toxic but I have a bad back and my husband is building the kitchen so this one is on me.  I have children who can help but any machine aided or grown man kind of materials are out.

I had considered doing something like cedar and rubbing an oil in to lengthen its life but I was worried the cedar might inhibit growth since it won't be sealed.  Does anyone know?
 
Chris Sargent
Posts: 54
Location: SE Alaska
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We did our deck shou sugi ban style.  The deck is made of cedar 2x6's, each individually burned on all sides and then treated with lindseed oil.  The deck is just 8x25 ft.  It did take quite awhile to burn all the boards but I love the look of it so it was worth the effort to me.  We just finished it last fall and so far the durability seems ok.  It beaded up water really well all winter but I think we will need to reapply oil annually.  We live in a rainforest so it's pretty much always wet so treatment for weather and rot resistance is critical.

On the front of the deck I also build full length planter boxes.  These were also done shou sugi ban style.  I did a longer burn on them so they are pretty much entirely black but not to the point of the alligator charring.  They are only about half full of soil and not planted yet.  So I can't really comment on how they'll hold up.

I have done lots of other cedar beds.  Some treated with oil others not.  Cedar beds will last a really long time on their own so I'm not sure treating with oil really adds that much.

As far as the oils in cedar harming the plants.  Its not an issue.  Pretty much everyone the gardens in my area uses cedar raised beds (again because we live in a rain forest and need the drainage from the raised beds and the rot resistance of cedar).  I've never seen or heard of any ill effect even with fresh cut rough timber being used.  What little bit of oil is in the cedar isn't going to have any movement from the boards into the surrounding soil.  I frequently have plants that are growing right up against the cedar boards and don't seem to be at all effected.  So I don't really think that there is any issue at all.  
 
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