Black leaves Acuba Japonica Gold Dust

Morning all, I got creative and managed to grow these young Acuba Japonica gold dust, so I planted these on a week ago to eventually create a low growing hedge. Yesterday I noticed two out of 5 of them had black leaves, have I over watered them?!

 

Looks like a cold snap type damage. Were they hardened off before going in the ground?

 

Yes they were hardened off before planting in the ground. The others are all okay. I wasn’t sure if I’d overwatered them. Hopefully they’ll still be okay then. Thank you @flounder for replying