PlantFiles: Hybrid Trachycarpus
Trachycarpus wagnerianus x fortunei

There are two hybrids doing the rounds: this (aka x Takagii) and one with fortunei as the seed parent, which seems to be the most common. Plants with wagnerianus as the seed parent seem to have the stiffer, more upright growth of wagnerianus coupled with larger leaves from fortunei. Plants with fortunei as the seed parent usually show some of the wagnerianus characteristics, but they are not always as pronounced. Both hybrids are vigorous and x Takagii is particularly fast.

Seedlings of the latter from an October 2010 sowing and grown under glass, have large, vigorous root systems and produced their first true leaf fans at 13 months. At 15 months they have been moved to 5L (1gal) pots and will be ready for planting out in a few months. These look as though they are going to develop into very fine plants with the best attributes of both parents together with hybrid vigour.

As to hardiness, here in the UK we do not normally experience the extremes of winter cold seen in parts of the US or eastern Europe. However, it seems logical that plants should easily be able to withstand temperatures down to -8.5C (16F) for short periods without protection.

I first saw this palm growing in Mr. Kiril Donov's nursery in Plovdiv. This is the guy responsible for making the 'Bulgaria' strain of Chusan palm widely avaiable.
When I saw it I thought it was the most beautiful palm in the world. It has the long petioles and large leaves of Trachycarpus fortunei, and the non-drooping leaves of Trachycarpus wagnerianus. Unfortunately, he wouldn't sell any of those palms, so I had to give up acquiring it until I stumbled on a guy who grows palms from a Belgian seed source. I bought one and it survived three weeks with no water immediately after being planted (! ). It has grown just one new leaf and still has to stand the test of our zone 8a winters. I hope it survives.
In the meantime, I have ordered 25 seeds from the same Belgian company and will try growing them myself.

Update April 7th, 2010: My three-year old hybrid windmill palm has survived a bitterly cold winter with temps dipping to -3 degrees F under heavy snow cover, in Krapets, Bulgaria. Heart of palms healthy, leaves half-burnt.