These photos are from a cold snap that hit our Olathe Horticulture Center awhile back. My colleague Dr. Alan Stevens took these photos and provided some commentary. The peony is first, then three iris. Click to enlarge the photo.
I’ve attached 3 pictures of freeze damage on Iris. Two are close ups of
buds and the third is of a whole plant. Look closely at the flower stems
in the whole plant picture. The curvature of the stem can also be an
indicator of freeze damage.
Iris flower buds are generally not sensitive to freeze damage issues.
There is only a very narrow window in bud developmental maturity where
they are susceptible. Because of this some buds on a plant may be injured
while others are not. This irregular damage can even occur on a single
stem where some buds survive while others do not.
Freeze damage on iris in mixed perennial beds is often overlooked because
of differing bloom dates between cultivars of iris.