Yes it would definately need protection. Leaf Damage would start to occur under 20 and root damage in the single digits.

Palmlover1. This Trachy is in Sterling VA. It was planted in 1994 and hasn't been protected since 1997 except for a little extra mulch. It has seen brief temps as low as -11 with no damage. I kid you not. Sterling is a cold zone 7a but like anywhere they have one freakishly cold night every couple of years. Its just a matter of getting it established. The three year rule. Check it out.

I just minimally protected mine this last winter--first winter in the ground. It was about 3-4 feet at time of planting last summer. I just wrapped the trunks with a string of white Christmas lights and then wrapped two white insulating blankets around the trunk (securing them with bungee ties). Between the blanket layers I wrapped a set of Christmas lights around the trunk. It really looked pretty over the winter because you could see the Christmas lights under the shear outer blanket. I left the leaves totally exposed though. (Personally, I don't see the point of growing a palm in the ground if you have to cover up the leaves in a plastic dome or mini greenhouse.) Although there was some minor leaf damage, it started pushing new growth in March and is growing vigorously now. Both are in a
somewhat protected microclimate as they are planted within a
few feet of the south side of the house. Minimum winter temp
was 11 F. above zero but went through a few snow, sleet and ice storms in addition to a VERY wet winter.