Washingtonia x filibusta growing in zone 6a Colorado

[Palmphile]

Does anyone have growing tips to protect my Washingtonia x filibusta this winter in Colorado Springs, CO?
I have had success growing Trachycarpus fortunei in this same spot through winter of 2022 with little to no real structure around the palm only wrapping with a heat cable and burlap. Granted it defoliated and though a frond was coming up the following June it eventually rotted out and died mysteriously. I was upset that it died but I attributed the defoliation to the soil drying out in the winter as the black plastic trash can over it blocked moisture to the Trachycarpus and the heat cable partially buried below grade dried the soil, but then again a plastic trash can wasn’t going to really protect from the coldest freezes and cold air from January Colorado nights!
 

My current plan is to build a 1/2” PVC structure measuring 18”x18”x4’ over the palm and wrap it with flexible aluminum attic insulation a few layers deep, and to continue the heat cable layer partially over the surrounding soil around the palm and around the trunk. I figured that Washingtonia would benefit from the kind of dry soil that actually damaged the Trachycarpus. I will cover the sheltered area with mulch and wrap the fronds up tightly. I am unsure if I can open the shelter up during the day as in the coldest months the daytime windchill can be below 30 very often. This is what I did with the Trachycarpus. I mean day time temps not including windchill can be chilly at best but certainly not frigid.
Though as mentioned in a previous thread, Colorado has high solar radiation due to its high elevation over 5000’. So what should I do, any tips? I really want this palm to make it through as I’ve actually grown it from seed back in 2021.

[SeanK]

Just a thought. . . .smaller palms are easier to protect than larger ones.

[Allen]

You will need the box method

https://www.youtube.com/watch?v=uAy2LcGeMwU

https://www.youtube.com/watch?v=21uvp_QznhQ

 

[MJSanDiego]

I will preface this by saying that the cold tolerance of a Filifera is less than a Trachycarpus fortunei, so knowing what happened to your Trachycarpus should be an indication of the success with a Filifera. You can box up the Filifera, but unless there is a major uniform heat source inside with insulation, and no drafts, it simply won't survive zone 5b. Perhaps it could survive one season with some box method, but it will be a slow decline overall. This is a time-consuming futile task. I really don't like to be the only one raining on the BBQ, but this is just ridiculous and makes no sense