In article ,
Kay Lancaster wrote:

On Tue, 24 Jan 2012 18:11:40 -0800 (PST), Higgs Boson
wrote:
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.

Can't tell from the photo. The leaves look equitant, which means the
plant is likely in the Iridaceae or something closely related:
http://www.ces.ncsu.edu/depts/hort/hil/hil-8701.html

I believe H.B. was referring to the shorter plants in the picture.

Could be poor handling in the nursery, poor handling by you, poor planting
site, fungal disease, bacterial rot... I'd start by digging up the blackened
plants and examining the roots and leaves for signs of rot or infestation.