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Re: HYB: Daylength independent

Thanks so much for digging up data, Chuck.  Interesting stuff.

<Many biennial
species have a vernalization period, which can vary in period and
temperature. Typical vernalization temperatures are between 5 and 10
degrees Celsius (40 and 50 degrees Fahrenheit).>

This temperature range matches my perception (sorry, no data, just casual observation) of temperatures needed to trigger fall bloomstalk production in "cold climate" rebloomers here, both those that seem to bloom independent of daylength and those that only rebloom in the fall.

Some cultivars rebloom much earlier in the fall than others, depending on when that period of cold comes - most years, we don't get temperatures that cold until August. It takes about 6 weeks after that for blooms to open.

Flower Bud initiation in iris  typically sets the end of  August  in
Japan (Where the research was done)  with daylight temperature  was
average 26C. Thus probably earlier in cooler climates. > [that's about 80oF]

80oF is about the daytime temperature when nighttime temperatures drop to the 40s and 50s at night.

Temperatures are erratic here, so we may get only one or two nights that low with an early cold front, but that seems to be enough to trigger stalk formation.

<Immortality  can sit in my garden with mature  size rhizomes and lots
of  leaves, but doesn't bloom until Mid to late August. This would
suggest that it is not daylight independent.
Forever Blue does bloom whenever a rhizome reaches maturity.

Chuck Chapman>

The peculiar thing about IMM is that she will make stalks thru the summer <IF> we get a cool night or two (doesn't happen every year), but most other rebloomers don't do that.

Chuck, can you come up with a theory that might explain IMM's different behavior where you are compared to here?

My guess it's some kind of interaction between daylength and temperature, but I can't figure out how it might work.....

Maybe she has to have longer days to keep blooming than you ever get in the summer????

A few other cultivars are 'summer' bloomers here - BELVI QUEEN, VIOLET MIRACLE, TEA LEAVES, but these three seem to require more of something (longer? less erratic? cool periods, less erratic moisture? ??) than IMM.

Wish I had been keeping temperature/rainfall records, especially the year when IMM bloomed repeatedly.
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.DiscoverET.org/etis>
Region 7, Kentucky-Tennessee <http://www.aisregion7.org>
American Iris Society web site <http://www.irises.org>
talk archives: <http://www.hort.net/lists/iris-talk/>
photos archives: <http://www.hort.net/lists/iris-photos/>
online R&I <http://www.irisregister.com>

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