Garden Q&A: How can I thicken up my Red Robin

You will need to wait until September but Red Robin responds very well to cutting

It is illegal in Ireland to cut or prune hedges between the 1st of March and the 31st of August, so you will need to wait until September before you touch them.

Question

My red robin hedge is looking sparse and a bit bare. How can I thicken it up so it looks good and full?