Penstemon are evergreen perennial plants that are increased by taking cuttings. They can be tender in hard winters so it is advisable to increase them by late summer cuttings in case the main plant is lost in the winter. This video tells you how to maintain Penstemnon at this time of year.
Take cuttings as shown in the video and insert in a mixture of peat and sand in small pots, do not allow cuttings to touch as if one rots it can spread to the others.
Put pots in a cold frame and once rooted pot on into small pots to over winter in the cold frame.
Alternatively the rooted cuttings can be left in their pots to be potted on in spring.
Do not allow cuttings to dry out but do not saturate either.