[Joe K]

Ash is the "King's Wood" coming from the fact in baronial England the ash trees on the king's land could be burned in the "green" state by the serfs - no piles of wood drying around the serf's cabin to reveal he had been "poaching." To burn the kings wood was considered an ultimate revolutionary act - besides keeping yourself warm at the king's expense.

As a wood resistant to decay, it doesn't work so well. Sort of mid-way between Birch (which can rot in a heartbeat) and oak (which rots but the mechanical strength can endure for quite a while.

Black locust is a wood that is environmentally sound AND highly resistant to rot. Grandmother had a stand of black locust from which she allowed me to cut and make a split rail fence. Each tree in that stand grew from the stump of the previous tree at that location - and it was cut perhaps 25 years before. And every stump of those previous trees were still there. As fenceposts black locust is good for 50-60 years in the ground - longer as rails. Black locust machines well in the green state, dries to tougher than ironwood, the only fault for dimension structures would be change in dimension during drying.

I might tend to use pressure treated lumber for this application. The usual source for pressure treated is southern yellow pine - which is NOT a hardwood, but will take on the biocide chemicals well. For a while pressure treated lumber/plywood was used in substitute for poured concrete foundations for houses - although the recent change in chemicals may have put this on hold.

The chemical in pressure treated USED to be Copper Arsenate - now being done with copper borate I believe which is less effective as a biocide, but more forgiving to the environment. Most pressure treated lumber comes "rated" for various degrees of ground contact and lifespan guarantee. You get what you pay for, of course.

Another one which has become popular is "Greenheart" which is a tropical specie which since the 1960s is the environmentally passable alternative to creosote ties and pilings. Its a bit expensive but pilings come with 30 year guarantee.

I would tend to the pressure treated as a most cost effective solution - and buy the best guarantee available.

It is possible to buy copper arsenate as a liquid and apply it to joints and cuts. This position used to be filled by "Cuprinol" - but that chemical has now been replaced by "Woodlife Copper-coat" which is like Cuprinol on a diet (EPA) Think the green appearance and smell of your childhood camp building. The Utilities use a product called "Tenex" which is like Cuprinol on steroids for things like crossarms and holes drilled for pole mounts. But you need a permit - and a need - to use this.

Joe K