Black Locust Outdoor Decking Question

[D6c]

You know it's funny about fence post,pole building post or power poles .The part below ground lasts forever it seems .Just a few inchs above or below grade is where they rot off .

When they send work crews around to put a preserative  paper around utility pole they only go down about a foot below grade .

Nice deck BTW .

The first foot or so below ground is where microbes are active...get down a ways and wood will last about forever.
That's why when I built my pole building shop I used plasti-sleeves on the poles.  I'll let you know in about 30 years if it worked.
https://www.plastisleeve.com/plasti-sleeve/

[Offthebeatenpath]

It sounds like you have plenty of supplier options, but I just met a rep from a company last week in West Virginia that specializes in black locust. I was impressed with what I saw of their product. 

Robi Decking, Clarksburg, WV 
Black Locust Lumber and Decking - Robi Decking.

[moodnacreek]

A little off the decking subject; in 1980 I put 3x3 locust [square] posts in the ground and 25 years latter I pulled them, just a 1/2" ring of rot on the outside. 6x6 put in 15 years ago here are gone underground, termites.

[treesparrow]

My first reply.
   In 1996 my friends and I built a shanty with a Black Locust deck. It is still solid although weathered. We have never treated it. It air dried for only a few months, not sure exactly how long before we installed it. We used an air cartridge nailer through the 1" roughcut boards. The sawyer that cut the boards said it was some of the hardest cutting logs he had ever cut. This was with a circle mill. The logs must have had tension and would bind the blade. This was a sawyer with lifelong experience and a man hat doctored and hammered blades.
   As to the discussion of wood rotting when in contact with ground. I worked for Osmose treating poles in the 70's. We dug down to 18" below grade, a point below which we were told had to little available oxygen to support rot. Well having dug many poles it seemed they were sound at that depth even if rotted above.