Use a cheaper, wireless indoor/outdoor thermometer.
Place batteries in both parts as per the instructions.
Before burying the outdoor sensor, wrap it in several ziploc bags.
Bury it down about 5 or 6 inches (10 to 15 cm), and cover it with soil and mulch.
Bury it at the depth of the bulbs or plant roots.
It then can give you an idea of the soil temperatures the bulbs and peony roots are experiencing. Most will grow roots between about 38 ºF and 45 ºF . ( 4ºC and 10 ºC).
Even though the air temperature is freezing, it may be warm enough for root growth in the soil.
Right now, our outdoor temperature is about minus 10 º C or about 17 º F.
My daffodil bulbs are experiencing about minus 2.2 º C or about 30 º F.
I also placed another remote in a styrofoam cooler, which contains my Martagon lily starts.
The styrofoam cooler is in an unheated car port. The lilies are experiencing temperatures just below freezing as they are at about minus 1.3 º C or about 31 º F this morning.