Since penstemons are often semi-evergreen in our climate, they are often lumped with the above. They also have a need for really good drainage and sometimes the challenge of winter cold combined with our winter wet can push what are normally "hardy" plants over the edge. I prefer to give them the best possible chance and that means waiting until after the worst of winter to remove any possible winter damage. Ditto things like nepeta, Russian sage, Caryopteris, lavatera, hardy fuchsias....wait until late winter or when new growth starts to prune.

Even though it was not written specifically with our PNW climate in mind, The Well-Tended Perennial Garden by Tracy DiSabto-Aust is an excellent resource for this type of information as well as when/how to divide and other perennial culture and care issues.

Otherwise, there is not much you cannot clean up or trim back as far as herbaceous perennials are concerned. Some like to leave old flower or seedheads in place to offer food for wildlife and for winter interest, others like to tidy things up completely. Your choice :-) Pruning back deciduous or most flowering shrubs is much more on a case-by-case basis and that is determined by whether the plant produces flower buds on new growth or second year growth. Just Google the specific shrub for that information or get yourself a good pruning text.

btw, cutting back or cleaning up herbaceous perennials for the season is not quite the same as 'pruning', a term that is usually limited to woody plants.....a small gardening semantics thing :-)

In the fall I run out when the weather is agreeable or I'm in the mood. Be sure to wear heavy gloves so you don't cut yourself snipping up the pieces.

If there is a lot to cut back & the weather is dry even easier is to throw it out on the lawn. It makes a bit of a mess, but after a bit my husband or son mow over it along with any fallen leaves. If we bag it we dump out into the garden cart or on a tarp to dry a bit if needed, then spread around between plants. If we don't bag it, we just go back & pick up the clumps to use as mulch.

Doing it this way I don't have the work of hauling it to a separate compost pile & haul back to the beds when the compost is finished. So far so good!