If there is no wind blowing at night, the -1ºC will be just -1ºC.
From what I read, they can take it.
We have 3-4ºC at night with 20-30 km/h wind, and it´s supposed to be felt like -1 or -2ºC.
You can put fresh manure at the base of the plant for protection.
You may wanna check them daily.