How and when do I cut back Helianthemums to stop them becoming woody?

arent they a plant that doesnt go woody? its in my head that they dont but i could be wrong

I take the shears to mine as soon as they've finished flowering, then they give me another flush of flowers!

After this, another hair-cut. In the spring, I sit and cut out any dead pieces from under the (large) clumps. This keeps them healthy and non-woody!

Be a bit ruthless with the shears, they don't mind, just do leave some green, though! LOL.