Leggy Guelder Rose

I have a small hedge of Guelder Rose plants that have a lot of new growth on the upper half over the past few weeks, but they are very bare and leggy looking at the bottom. I'm wondering if I could cut them back hard to make them fill out a bit, and if so, would this be a good time of year to do it?

Or should I wait until a different time?

 

How to Grow Guelder Rose | BBC Gardeners World Magazine