I don't cut mine back until the spring - and then only as necessary - I think the top growth may well give some protection to the plant over the winter, as not all gauras survive.

I found out from another member that you can easily take cuttings in water in the summer - so at least I shall still have my favourite white one if the parent plant dies!

Yes, I agree.... I leave trimming my Gaura plants till the springtime, and then a light trim... It isn't easy to predict which of the plants will survive through the winter...

Gaura cuttings in water make roots very easily... I use rain water.
Don't change the water... Keep the cuttings in the same water...
My blog entitled "Cuttings Rooting in Rainwater"
[ 27th Nov. 09. Blog #20 ] has some useful ideas if you look at the photos and then read down the comments from members in the thread underneath...
I hope this helps.:o)

Well....I have cut mine down as I found last year the winter wind whipped them about....I have left them a third in height.