Mike, I find that Gaura can get very big and woody after a 2/3years and grow increasingly tall each year thereafter. This means they need a lot of space to grow into but can look quite spectacular. I normally cut most of mine back in the late autumn, before the really bad weather starts and when they have just about finished flowering. Some I leave though for winter interest as the stems often turn a lovely bright red colour. I cut them as close to the ground as I can - I used to be afraid of loosing them but have found that even when we get a cold winter they come through OK as they have a deep tap root. Now I tend to take out any that are obviously getting past their sell by date and allow self sets to replace them. I am never short of these and try to weed out unwanted ones in the spring before they get too big and get that tap root down! This year, to try to prevent every mature plant growing too big I cut back the new growth on some to encourage later, and hopefully shorter stems but by the end of the summer they were all much the same! At this point I cut back all the long, woody stems on some plants, leaving just the younger green ones. Due to a warm autumn and some decent rain these are still flowering profusely and at a lower level.
Gaura is an easy plant in some respects but does need a bit of work to get the best out of it if part of a "organised" area - give it its head in a larger, wilder area and it is stunning.
