I bought five of these (rather pricey) plants for planter box on my
front porch (N.facing).

http://tinypic.com/r/2i7yfb/5

They did fine until I noticed the far right one was turning black.
Now the one next to it is also infected -- or whatever is wrong.

I didn't save the tag, so does anyone know the name?

Also why this is happening, and do I need to move the other 3 to avoid
whatever it is?

TIA

HB