dieback penstemons

The leaves in the centre sometime go brown and appear to of died off if the plant is old or if there has been a lack of water. It happens all the time at the nursery where i work, if we miss a few days watering esp. if they are in pots, the centres go brown and look dead.
Remove the dead leaves and after flowering dead head and new shoots will appear. YOu can even do if flowering now and it will bush out and flower agian. A feed and water would be a good idea too.

A picture would be nice to see if this is what im thinking your problem may be.

I think I would also take cuttings from the plant - non-flowering shoots. I root mine in water, which works well for me: some people root them in gritty compost. Now is a very good time to take them!