Every two or three years we set fire to our two pampas grasses in the old herbaceous border, and the weather was perfect for this job on friday - very dry for the last couple of weeks, a gentle breeze, and before the grass has started to grow again.
It has a certain amount of naughtiness this job, like you are not really supposed to be setting plants in the borders alight, but if you have ever tried to tackle a large pampas with loppers and shear, believe me it is a lot quicker and easier and you end up with less cuts to your arms! I know there is an opinion that setting pampas grasses alight may damage the crown of the plant, yet in the 12 years we have been practicing this, they have not suffered.
The 'after' photo shows the result, but it will look fine as soon as it starts growing in spring.
Remember to check for hedgehogs before you start though!