Trachycarpus fortunei should do the trick (Takil hasn't proven to be that much hardier, if it's even hardier at all, so it's not worth the effort). Most Trachys sold as Takil are actually Nanital which are beautiful palms, but the cold tolerance isn't really different from T. Fortunei.

If you keep your palms in pots, that will expose them to a LOT more cold so you might have some issues that you wouldn't have if you planted them in the ground. If you have a garage (does not have to be a heated garage), your can drag your Trachy in there when nights get below the low to mid 20s (or whenever there's going to be a bad snow or cold rain). That would ensure that it stays healthy, give you the tropical look 50 weeks out of the year, and would not be a lot of work. Otherwise you might want to think of a spot in the ground, even if you have to dig something else up.

Needle palms and Sabal Minors are also very hardy and I have had a lot of luck with European fan palms.

Good luck!
-Alex

Here is a link that might be useful: My Plant Blog

Thanks for the information Alex,
They actually sell fortunei at the home depot where I am for $18. I have been skeptical about them because the tag says zone 8. I believe because of the city, I have a bit of a heat island effect. The temperature will rarely get below 10 degrees, and if it does, I can take extra efforts. I would drag them in, but the 3'X3' pots I will be planting them in are made with 3 in thick concrete and weigh about 300 lbs. I also don't really have any in ground space. Mine is a row house with a tiny yard, but is an end unit so there is a lot of area along the side of the house (south west facing).

Perhaps I can use a smaller pot so I could get it inside. How much root space is needed? I could also go to the extreme and build a box around it.

Cheers,
Werner

This post was edited by klavier on Mon, Jun 24, 13 at 21:49

Most of the Baltimore is 7b. Windmills do fine in 7b. Always good to protect palms first few winters on the edge of their range.

Just as an FYI I have 2 Windmills that I bought at Home Depot last spring and left them outside in pots over the past winter with no issues. I am on the Eastern Shore in MD and I think it was a fairly mild winter but there was absolutely no damage to them at all. I have yet to cut off a palm frond since purchasing it. It has at least doubled in size in a year. Since they made it through last winter and have grown I may take additional precautions this winter if it gets bad or move them into the garage. I did have them on a brick patio up against the house where they were sheltered from rain and snow.