Fall is an ideal time to plant native perennials. Even when temperatures drop above ground, temperatures remain warm below ground and are ideal for root growth and establishment well into fall.
Planting by early October gives the roots plenty of time to establish, which will help the transplants acclimate and allow them to gradually go into dormancy with the onset of colder temperatures.
Water transplants thoroughly when they are planted. Try to water less often and more deeply. This will promote deeper and stronger root development.
By late October, back off on watering in order to allow the plants to harden off.
Do not fertilize fall plantings. Fertilization causes transplants to put energy into new vegetative growth that can be damaged by winter conditions and will also suppress the establishment of roots.
Do add a 2-3 inch layer of mulch or compost, when the temperature starts to cool, at the base of plants making sure to leave some open space around the stems. (chopped leaves are great for this and most everyone has them on hand!)
As long as the plants are well anchored and mulched, frost heaving will be prevented.
Your native perennials will go into dormancy for the winter and come back vigorously next spring!