These are good at providing heat to the area they are attached to,you would need to wrap the trunk to keep heat close to it.I tried this last year in my single layer(pvc-plastic)umbrella greenhouse 44"x49"it provided no heat to air surrounding palms,then I tried a 100wt light bulb that provided 3-5F,after that I used a 125wt heat lamp,this added10-12F I used this the rest of the winter,on cold nights(below 0F)I used a layer of plastic and or a tarp this added 20F but beware the extra layer of palstic added 50-70F during a sunny day in mid winter and it would be very easy to fry your palm!This method was for T. fortunei I would not advise this for a washy