Don't cut it back yet, Mary, there could be lots of frosty weather still to come. Have a look at the base and there should be growth appearing at the base. Once this has started to develop and frost is reasonably past (End of March here), you can cut it back to just above this new growth and it will bush up and flower again.

yes too soon now and when you do get round to pruning you can use some of the top growth for cuttings if you want more plants.

Thankyou so much, glad I left well alone and will wait. I have never been quite sure how to treat Penstemons, so very glad of tips. I meant to say bushey not busy, but guess you knew what i meant. Mary