Great article Barb.

I have to question any study where claims are made for "palms"where cold hardy palms
(growing in cold areas) specifically are not mentioned.

Saying palms don't or palms can't -makes me wonder,the actual wording is-

"However there are plants (e.g. many C4 plants, palm tree leaves and tomato plants) that have very little or no hardening capacity "

Absolutely no way I group hardy palms and tomatoes leaves together,seriously the leaves of tomato plants and Trachys,Needles ans Sabals?

This kind of a study is pointed at crops-mostly.

Most of the findings,etc are based on tropical plants/PALMS,varieties of palms (fruit producing) which are not cold hardy..
at all.

Trachys are for sure able to harden of over the fall and early winter.

By late January my Trachys can easily take single digits(f) with no damage.

Lot's of good info in this article-the comparison of freeze and drought stress in regard to
cellular movement of water,carbs etc.

Keeping large palms dry going into winter is not an easy task(especially the crown area)but
look at the numbers John in Colorado came up with,way lower cold tolerance in his Trachys
than those grown in the wetter southeast U.S.

My small Trachys in styrofoam covers survived with no heat,most of the time
over the winter temps stayed 20-35f,so they were frozen for long periods.

I didn't even look at the article(s) that Barb posted. There is some interesting info there for sure.

Jim- That article Erik posted used a lot of Johns work (Fitzroy 2004, or something like that) to establish the minimum temperature and GDD recovery info.