Well I have a Trachycarpus wagnerianus that was planted in april 1996.for the first 7 or 8 years I covered it in January and the first half of Feb. with a 4 mil. clear plastic box, with basically no winter damage, now for the past 5 years or so I have given it no protection to just a fabric plant sleeve(to prevent heavy wet snow damage) and some cardboard wrapped around the trunk,with no- to moderate winter damage- moderate means 50% of foliage looked ratty and needed removal in april, may and june, as new, or just before replacement foliage emerged. It is now 10 and a half feet tall(from soil to tips of top fronds) I hope to post a picture soon. I also have Sabal minor along the foundation, about 8 years, and a little needle palm planted in a bed of ivy, about 2 or 3 years, no protection except maby wiltpruf.