I have all 4 in ground,and I protected the 2 old ones,in the Backyard,but ,I am not allowed to protect the 2 plants in front of the house.
So I placed chicken wire around them, and ,put about 6 to 8 inches of leaves at the base of the tree in the interior of the wire circle.
Chicken wire is needed also because Squirrels ,munch on the wood of young trees,so that is why.
In the Spring,all 4 came with minor frost damage,to about 6 inches at the tips,some tips died up to 10 inches.
They recovered well,and now I have them loaded with fruits,the older ones had Breba too,about 6 breba fruits each.