Protect slightly tender perennials
Some herbaceous perennials such as penstemons, salvias, Verbena rigida, gaura and alstroemeria are borderline hardy (they’ll survive a mild winter but may be killed off if it gets colder).
Take insurance cuttings... Taking cuttings in early autumn will ensure you have plants next spring, or you can lift plants and pot up into containers that can be brought under cover.
...Or mulch the plants Another option is to mulch these plants now with a thick layer of chipped bark around the base to protect the plant from sharp frosts.
Don’t cut them back Leave any foliage in place because this will provide protection for the crown of the plant and the roots below ground.