I have one T. Takil and one smaller T Fortunei I am overwintering using supplemental heat.
They are both going through their 2nd winter in the ground. Last winter, we had a minimum low of -16F. I had low-wattage (40w and 25w respectively) bulbs that would turn on at dusk, and then back on at dawn; reasononing was that any sun during the day would do the trick.
Both plants defoliated--in fact I really though the Fortunei was dead, but both shot up a new spear in May.
This year, I'm upping the wattage on the smaller Fortunei to 60w (keeping it on continously unless we have all-day sun), and for the larger Takil, I have a micro space heater thermostatically controlled from 35F to 45F. Some days the low never gets to 35F so the heater doesn't even come on.
My goal is for them to keep most if not all their leaves so they won't be playing "catchup" in the summer.
As we speak, the outside temperature is 23F and the inside temp for the Fortunei with the bulb is 60.3F (both using wiress sensors).
I use a very low tech, semi-clear containers (you can get these at Target, etc.), wrapped in bubble wrap and then covered with 1mil sheeting material. Then I cover the edges with mulch (and now snow). They are cheap, reusable and work great. You have no worry about drying winds.
For keeping up the humidity, I also supplement with an open container of water. To help with the heating, and to moderate the temperature, I spray-painted black 1-gallon milk jugs (higher heat absorption).
It sounds like a lot of bother, but it really hasn't been, and I can reuse the containers until they outgrow them. That will be a good problem to have.
This Spring I think I'm going for the big 15 gal. Trachy, although that will entail building a structure.
If you havn't already, sprinkle the crown with a copper-based fungicide, once now and then at least once again around late Feb/early March. This should prevent spear rot, many times the ultimate winter killer. Good luck.
Estiva
This should give all of us a little more confidence (source The Weather Channel):
milwaukee has mature palms?
