[andyww2013]

Hi,

Just finishing off some structures, part of which shall be in contact with the soil.  Was considering painting with bitumen type paint.  This would ensure against rotting but would probably leech a whole load of nasties into the soil.

There is probably no such thing as non-toxic wood preserve however does anyone have any recommendation as to least toxic stuff that actually protects wood?

[TonyB.]

Most modern wood preservatives are non toxic once dry.

If you can do not embed in concrete. Wood lasts longer in just soil as the concrete provides a water trap.

[hasbeans]

I think bitumen should be last on your list as it's nasty stuff to put in the soil.  If the wood is tanalised, then using ensele or other end grain protector helps on any cut ends and drilled bits.  Not sure any water based preserver would be worth the effort.

Can you put a few inches of gravel between the wood and the soil?  It might help the wood stay a bit drier.

 I've also had some success using old bits of oak or teak (scavenged from discarded and broken garden furniture and such like) at ground level or below and fastening whatever I've built to these.  Oak and teak take quite a while to rot, especially underground away from oxygen.  Charring timber is also supposed to work well!

Depends how pretty it has to be I suppose!

[rowlandwells]

I've used both bitumen and old engine oil first of painting the wooden post's and leaving them to completely soak in the timber for several days same goes with the old oil process the post's are still holding up the fence we put up some years ago in a planted flower bed with absolutely no problems  same with the oil dipped post's there holding up a field fence also no problems  the grass is growing round them very well

[al78]

I'm trying this, both on my greenhouse base and raised beds:

https://www.gardening-naturally.com/eco-wood-treatment

Someone said don't embed in concrete - oops, too late. I put wood stakes at the corners of my base and set them in postmix.