----------------- Cold tolerance ------------------
Now as much as I would love to say that you can grow a windmill palm without protection here in New York City, USDA zone 7b, the reality is that you can't long term. You could be the exception if you have an incredible microclimate, but I have seen so many people try and while they can sail through a mild winter and get by during our average winters, anything a little colder than usual always knocks them out. They can handle more cold in southern states where the sun angle is a bit higher and the days are warmer. But anyway if you have any questions leave a comment below. I want to get into the positives because anyone serious about this hobby whether you are in a zone 5 or a zone 8, should have a windmill palm because they are beautiful and very tough.
I give mine pretty minor protection during the winter. Protection goes on when a bad storm is coming (to keep moisture away from the growing crown), when nighttime temperatures drop below 18F, and when days fail to get above freezing. And my protection method is very basic since I am not too handy when it comes to building things. Just some lights, a frost cloth, and a plastic garbage bin gets the job done. Just make sure not to use LED lights since those do not generate heat. I use c7 or c9 light strings since the bulbs are nice and large and they emit a lot of heat.
----------------- Growth Rate ------------------
I've been growing my oldest trachycarpus since 2009. They were just baby 3 gallon palms when I planted them out. Now they are taller than me and are the proudest thing I grow. I know people who live in colder climates who have had even faster growth than this, but here is what can be achieved here in New York City in 7 years. There is an expression that goes the 1st year a plant sleeps, the 2nd year it creeps, then the 3rd year it leaps. I found this to be very true with windmill palms. It grew very little the first 2 years in the ground but after that took off! The first two years I had it, they actually looked very unhealthy. Now I think they look as healthy as they would in a mild climate.
In the middle of these 2 trachycarpus is a Livistona palm which I've had in the ground since 2010. It's only hardy to zone 8b and usually defoliates completely with temperatures in the low 20s, but it always comes back with some protection. A great perennial palm. As you can see it really has not grown much in the past 6 years unlike my trachys!