Penstomen

I cut mine back so that they dont get too leggy. I usualy do it in spring because I like to leave everything till then if I can so that there are loads of seeds and dropped leaves for the birds to scratch about in on the top of the soil during the winter months.
Lynne x

Keep deadheading for now to encourage more flowers then tidy them up late autumn and spring.Ours are producing a second wave of flowers after deadheading.

Definitely dead-head them, as Grenville is right - they keep on flowering well into the autumn if you do. Leave the last flowerheads on as these plants are not completely frost-hardy and this gives a little protection. Then in the spring when the new growth starts, cut them back to where they are shooting. Take cuttings now as a fall-back, too, as some Penstemons are short-lived plants anyway.

When I cut mine back in the spring I have managed just to strip some lower leaves off of the bit's Iv'e cut off and pinch the top off and just push them in the ground.
I have got loads more by doing this instead of just putting the off cuts on the compost.

You definitely have green fingers, T&T!