Cob: Waterproofing posts?

[Max Vittrup Jensen]

Hi! I'm newto this list, and am enjoying it a lot! I am located in the
Czech republic and planning a small cob cottage with an 'ecover'
grassroof, here in our ecovillage. I hope to start the post framing
(necessary to hold the load of the roof) asap. but am uncertain about
how to waterproof the ends of the posts I'll stick in the ground. I'll
like to avoid using concrete.... Is it OK to do this in the wintertime?
(presently it's just around freezing here)   Any suggestions? Or a
reference to an earlier posting? ...Oh, any great do and don'ts on a sod
(grassturf) roof?   Thank you heaps!!
Peace and Love, Max -The Great Dane!