Q.How Do I Protect Kaffir Plant in the Winter
Kaffir plant winter protection (southern MD, 20745)–7 years old, maybe older.

Certified GKH Gardening Expert
If you expect frost or freezing weather, make sure that the tree is covered at night (a bedsheet will do) and that that the covering is taken off first thing in the morning. Here is more information: https://www.gardeningknowhow.com/plant-problems/environmental/frost-how-to-protect-your-plants.htm
https://www.gardeningknowhow.com/plant-problems/environmental/protect-plants-in-freeze.htm
https://www.gardeningknowhow.com/plant-problems/environmental/protecting-plants-winter.htm