Protect my existing wooden fence from woodchip mulch / food forest soil

My back garden is enclosed with a wooden fence that the previous owner installed. I’m guessing it’s pressure treated yellow pine using copper azole as that’s what they sell in local box stores.

Initially, I wanted to protect the fence from rotting. I’m adding a foot of chip right to the boundary as I don’t have much space. What ever breaks down the chip will eventually decompose the fence, so the longer I can delay that, the better. My solution pre permies would have been to use 6x1 pressure treated boards. Or a cheaper board and a plastic barrier. Now I’m thinking of a naturally rot resistant timber like cedar, except I’m in Eastern US so it’s rare and very expensive. I’ve heard of people using black locust for posts but not boards and searching doesn’t bring up anything useful. Next option would be white oak, but I have no clue who sells that as well.

Which brings me back to the stuff they use to pressure treat wood - copper azole. Doesn’t sound like the kind of stuff I want leaching into my food forest. So maybe a plastic barrier is the lesser of all evils?

Any thoughts? Have you run into this problem when you started your food forest?

I haven't faced that exact thing, but I have several timber raised beds and faced the wood choice in their construction. My decision was to go with the cheapest untreated wood I could find and just assume I'll replace it in 5-10 years. I have fir that's been in contact with soil for almost 2.5 years and most pieces aren't really even showing signs of getting ratty (but it does vary a lot from stick to stick). So I'd be inclined to tack (or maybe just rest) untreated 1x6 stock against the fence posts to hold back your mulch.

When we hired someone to build our fence I requested a quote for cedar.  My wood of choice is redwood though it is expensive.

there are several wood preservation methods that you might consider:  Charring and borax are the usual ones I read about and we have used the charring method.  There are several Japanese methods though I can't think of the names.

Here are a couple of threads that may interest you or others:

https://permies.com/t/22394/charring-effective-treatment-ground-preservation

https://permies.com/t/177032/Borax-Wood-Preservation

Awesome - I like the idea of cheap boards and charring.

My fence is made of cedar off cuts.
If you have a sawmill that sells them, I found it to be totally worth the money.
I still wanted to protect it, so I used tiles, big ones from a reuse center, held in place with fender washers and deck screws.
Next time I will try cement board,  from the same source, and I  might parge it with strait cement.
Aluminum flashing is a reasonable choice as well.

I went for the ‘cheap boards’ and replace option. The boards were free - all upcycled from stuff I found in the basement, mostly the previous owners shelving which was in the wrong place. If I’m still here in 5 to 10 years then I’ll looking to some of the other options.

Thanks for all the tips. I’m yet to find a ‘proper’ saw mill, all the lumber yards I’ve visited are only interested in working with contractors and there’s no actual evidence of anything being milled on site. They’re what I’d call ‘builders merchants’ in the UK.

Edward Norton wrote:I went for the ‘cheap boards’ and replace option. The boards were free - all upcycled from stuff I found in the basement, mostly the previous owners shelving which was in the wrong place. If I’m still here in 5 to 10 years then I’ll looking to some of the other options.

Thanks for all the tips. I’m yet to find a ‘proper’ saw mill, all the lumber yards I’ve visited are only interested in working with contractors and there’s no actual evidence of anything being milled on site. They’re what I’d call ‘builders merchants’ in the UK.

Until this picture I totally misunderstood what you were trying to do. And now you have done it, so my thoughts are now "after" thoughts. But anyhow, for future readers.

My two thoughts.

1. The wood chips will tumble down where mounded, but it should reach a somewhat stable level as it breaks down. So you could just end the wood chip mulch a foot or 30 cm back from the fence. This would also give you some room for cutting grass.

2. If you had a lot of field stone you could make an edge border with that. It would easily hold back the chips. But it would be harder to deal with, since you can't scythe/mow easily around rock borders, and unwanted perennial volunteers love edge borders like that.