I've cut, split and burned some Siberian Elm in the past... mostly stuff the power company cut down along a right-of-way. In the round, or even split and stacked in a shady spot, it will rot relatively fast. But split and stacked in a sunny, breezy spot it will keep for 2-3 years or so. Do not stack it in triple rows... the center row will turn to something resembling a large hairball. I've never been able to find a reliable source for green moisture content... but it must be something 'round 100+% because it will lose ½ or more of it's weight during seasoning. It ain't as bad as willow or Basswood, but it does get pretty light-weight when dried... and it will shrink noticeably (stacks fall over). Like most any elm, it will shed its bark early in the seasoning process; if you toss the bark, rather than burn it, the offensive "stink" is greatly reduced... as is the ash left behind. With any "green-cut" elm I prefer to wait for the bark to release before splitting, allowing me to stack bark-free splits. It lacks the excellent coaling properties of American Elm and burns somewhat faster, but, if well seasoned, it does throw a decent amount of heat during that short(er) burn time... it won't leave you with a hot pile of coals to wake-up to in the morning. Burned before fully seasoned it is miserable stuff... smokey, stinky, and little heat.
I don't believe I'd rate it as low as crap or trash... I'd burn it before I'd burn Box Elder, or even Basswood, willow and the like.
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