Nellie Stevens hollies turning black - what to do now?

[OKSooner]

Question: I planted three 8' B&B Nellie Stevens hollies for a customer last Tuesday. Bought them at a reputable nursery about 10 miles from the site, drove them there slowly...

Planted them slightly above grade, and used new topsoil with organic amendments to backfill. Mulched with pine bark.

I've been watching them all week, and when I checked on them today, two of the three of them were turning black. Not a spotted black like leaf spot, but just plain ol' black, from the tips of the leaves inward.

Based on some things I've heard, I wonder if they might not be getting enough air to the roots for some reason. Overwatering, perhaps?

If that's the case, what can I do about it? :help:

Thanks...

[Lawnworks]

Is it black dust on the leaves?

Or did you have a frost and the new growth got burned?

[OKSooner]

No dust like any kind of mildew, etc. No frost either, the temps have gotten down to the upper 40's around here.