Re: TB: low bloom height this year
iris@hort.net
  • Subject: Re: TB: low bloom height this year
  • From: P* <p*@bellsouth.net>
  • Date: Sat, 01 Jun 2013 23:55:24 -0400
Thanks Linda! You explained my all observations. If I clock back 6 wks then just my normal weather, if there is such a thing these days, is going result in hit or miss for E to M. And, as I observed, less so as I go post M, even within the same clump. I have gone from 20 or so to 200 cvs in two years and after orders go in this year I'll be up to 350+. Yes - the bug bit. I need to develop your spirit about the whole affair - chalk up the losses to learning. I'm gonna learn a LOT about who can hang with just the normal weather here much less the bad.
Have you experimented with row covers? For display beds that would be a lot faster than putting temp mulch down and pulling it off later. Ugly but no uglier than stunted flowers and rotting fans.
I have a frostier, wetter bottom and less frosty, drier upland. Cardoon is supposed to overwinter better up than btm according to the books. I never loose it in the bottom & loose every year up. I speculate soil temp fluctuating might be less in the btm and/or the soil staying colder keeps the plant more hardened off. So I'll experiment with the irises for same. 

Shaub SW NC Z6b

On 6/1/2013 8:07 PM, Linda Mann wrote:
The critical timing for stalks being stunted seems to be about 6 weeks <before> bloom in TBs here. This is before stalks are showing or can be felt in the fan.
So that's usually some time in March, well before last average freeze date. Critical temperature seems to be below mid-20s. Anything below about 20, especially if night time temperatures have been above freezing for ? a week?, will knock out just about all TB bloom the following month. Stunting can occur if temps are cold, but not cold enough to kill stalks before they emerge. & of course, all of this varies to some extent among different cultivars and effects are much worse if cold follows a really warm spell in early to mid March.
Those temperature thresholds are based on my experiences here for 40+ years growing irises - I'm in a low spot, shaded from morning sun by a ridge behind my house, so cold settles and stays.
Rotting terminals are another issue - on new plants, especially those coming from a milder climate, just plain cold temperatures seem to kill terminals over the winter.
On plants that are 'adjusted' to climate here, those late freezes that knock out terminals definitely set plants up for major rot problems. Some cultivars seem to rot more readily after that kind of damage than others.. 

Linda Mann east TN USA zone 7b

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