Why does emerald cedar turn black?
Why does my emerald cedar turn black as shown in the picture?
Certified GKH Gardening Expert
Root rot or a fungal disease are the most likely culprits. Overwatering or high rainfall could contribute to this, especially if water frequently gets on the foliage.
Keep the area around the cedar clean and free of fallen leaves. Once spring comes, prune off the blackened parts and dispose of them away from the garden.
Another possibility is sooty mold: