In article ,
Simon Avery wrote:
Chris Hogg wrote:

CH What is the best way to stop wooden fence posts rotting
CH below ground level?

There isn't one, sorry. Wood rots in contact with water.

It's not the water, as such. Both elm and oak will last for
centuries under water. The problem is the combination of wet and
oxygen just below soil level that allows fungi to flourish.

Untreated softwood lasts 5-10 years. (Dependant on soil conditions)

Treated, 10-20 years. (Larch can do this untreated)

Some hardwoods (split chestnut, oak, willow) will last 50+ years
untreated.

In the UK, just below soil level? You jest, sirrah!

From experience, softwood lasts 1-2 years untreated, and chestnut
or oak sapwood (the former well creosoted) about 5.

I haven't got much experience of the heartwood, but it certainly
lasts a lot better. Yew is the ONLY British tree that I know of
where the sapwood will survive being embedded just below damp
soil level for more than about 5 years.


Regards,
Nick Maclaren.