Your Dahlias have died. Dig deep and wide.
I use my shovel we call Bubba for jobs like this. Overzealous use of Bubba several years ago caused my plantar fasciitis.
Dahlia tubers should not freeze. NC people, low temperatures are headed this way.
This means it is time for your second phase of digging.
All your “BEFORE FROST” plants should be stored away by now.
Now is time to bring in your desiccated and dead looking “AFTER FROST” plants.
This group includes dahlias and Elephant ears. I bring in some “stock plants” of my different types, since I have too many to bring them all in.
I put a thick layer of mulch over the ones left outside.
ALWAYS keep the names of the tubers, bulbs or corms WITH the plant.
This year I punched holes in the plant markers and tied them to the tubers.
One year I wrote the names on the outside of the paper bags they were in. The bags rotted along with the names.
Dig up tubers. Cut back the stems. Clean off excess soil. I use a chopstick or skewer.
Put the tuber clusters in dry peat.
Plant again in the late spring.