Bloom signals for each species is a complicated arrangement of various
signals. Much new research is being done on it via the MADS-box genes,
governing signals for tissue differentiation, and signals associated
with it. This is more or less the plant equivalent of stem cell signals
in animals. Lots of new genetic tools to explore this. I recently
started to read a book "Photoperiodism In Plants", but stopped as it is
now grossly out of date with a lot of outdated information, even
though it was published in 1997, almost all of its conclusions are out
of date. The new information is comming in fast.
Most plants have a series of signals working together. I outlined some
of these in an article on rebloom genetics in British Iris Society
Yearbook, 2008.
Siberian Iris probably need a cold period of a certain number of hours
of vernalization betwewen temperatures of 4-10C in order to turn off
bloom inhibiting genes, thus enabling bud set and/or bloom. Your
plants in window may not have had these hours. Siberian iris would
seem to be a long day bloom trigger, meaning that they need sunlight
days of above a certain number of hours. While it is true some long day
plants need a certain period of short nights, most don't. Some plants
need a period of short days followed by long days, and some need long
days followed by short days. Some plants need temperature
differentiation between night and20days. For example, night s 10-15 C
cooler at night. Some need certain temperatures in order to do bud set.
Right now, it is only a best guess as to what siberian need.
Your information indicatres that the siberian iris ( at least the ones
you have) don't sem to be endo-dormant. Other wise they woundn't likely
be growing at all, unless they had an appropriate period of cold to
break dormancy. Eco-dormant, go into dormancy triggered by the
temperature, and restart growth after a few days of good conditiond,
warmth usually coupled with long days (longer then winter that is )
and this seems to be what your siberians are, that is eco-dormant.
I have an alphalla plant and an SDB in pots, placed in the house
shortly after winter set in. About mid november.end of One pot of each
under lights, with long day (17 hours ) and warmth. And another one pot
of each in a window sill in room with no extra light, cooler then other
rooms, but still enough for growth.. Non of these plants are showing
any growth at all. The iris seedlings in pots beside the ones under
lights are growing well as are iris seedlings in window sill, right
beside the test plants. Thus both of these are endo-dormant. That is
triggered into dormancy by short daylight, not by cold temperatures
(ectro-dormant). It will be interesting to see how and when they break
dormancy, compared to the ones outside that have had their20appropriate
cold period.
Plant maturity also plays a role, as you have noted, but your potted
siberian should have reached plant maturity by now.
By the way, I have found the TB iris need somewhere between 9-15 mature
leaves. This is count of total leaves produced by rhizome, over its
life span. This can be counted by total leaves , including leaves dead
or removed. The old leaves can be counted by leaf 'Rings" on rhizome.
Each cultivar has its own mature leaf count, and it seems to be
irrelevant in regards to where and what climate it is grown in. For
example, Immortality blooms with mature leaf count of 12, regardless of
where it is grown. Siberian may also need to have a maturity leaf
count, but I haven't looked at them to see.
Any information on mini experiments welcome.
Do you have great growth in your potted siberian? Or just barely
growing?
Are they in even temperature, or colder at night?
Chuck Chapman
-----Original Message-----
From: wmcdougherty@cs.com
To: sibrob@yahoogroups.com
Sent: Thu, 19 Mar 2009 9:24 pm
Subject: Re: [sibrob] Re: forcing Siberians
Hello,
Isn't the issue of force-blooming Siberians also an issue of the size
of the plant? In bearded iris you generally need 6 to 7 leaves to have
the plant bloom. I currently have sibs in a window which began growth
in early January no hint of blooming.
Botanically speaking, bloom is not an issue of abundant sunlight but
the duration of the absence of light.
Bill Dougherty
