CULT: bloom and cold injury
Depending on how cold it gets and the stage of growth the iris is in, hard
freezes may or may not affect this year's bloom. In my experience, daytime
temps are often in the 70's or even 80s as early as March, which gets some
irises all excited thinking it's spring, so they initiate rapid growth and
then get nailed by the next low 20s freeze. We go through many many of these
cycles every spring. Areas closer to the coast have these extreme
temperature changes somewhat moderated by the ocean. Cold damage is
amplified in my particular location because I am in a frost pocket (it gets
colder and stays cold longer than surrounding areas).
In my experience, bloom can be affected by freezes in the low 20s in March
once we've had enough warmth to get things growing well (peak tall bearded
season is mid-May). Bud primordia seem to be damaged inside the rhizome. (I
tried piling about an inch of soil on top of them this winter as an
experiment to see if that would slow them down and/or insulate them a bit).
Mid-late and late bloomers are usually not affected. Later in the season,
as average temperatures get warmer, and bud stalks become visible (assuming
they escaped earlier damage), bloom can be affected by even 'warmer' freezes,
in the upper 20s (stunted stalks, distorted flowers, dead buds).
And of course, all that damaged foliage makes a happy home for our friend
Erwinia and her cousin, southern blight..
Linda Mann firstname.lastname@example.org east Tennessee USA
enjoying a few irises in bloom (LOGO and I. germanica) and shaking my head
over all the cold injury - wonder what will make it thru to bloom season?
Several very hard freezes in the last few weeks (low to mid 20s) NOT
inspired to weed. But it has been a gorgous spring with spectacular
wildflower and other bloom.