That sounds good, Chad. I've puzzled over it for a few years. I tried to link it to day length at first, but that didn't seem quite right. The temps have been really warm when the fall germination began, yet warm temps and longer days shut them down in the spring.
Weather here is so erratic, it's hard to predict what conditions the seeds will be exposed to for any length of time. The process I've worked out that has resulted in much better germination rates means I have germination occurring from fall, thru winter and into the cool part of spring. But they shut off germination quickly in spring when temps stay warm for too many days and nights.
--- In firstname.lastname@example.org, chad schroter <charlesschroter@...> wrote:
> I would hazard a guess that the temperature swing is important, but not as much as the length of the daily temperature cycle. As we head into fall and the days shorten, the cooler part of the cycle is longer - even a seed underground can detect this and react the same way plants do to shorter days.
> Fall is very warm here in CA, but many trees are losing their leaves anyway.Â A line of London Plane trees near my office is dropping leaves now, but the parts of the trees which are right next to the street lights will hold their leaves well into the winter - proving that the 'decision' to drop a leaf is not made by some central reaction inside the tree, or by the ambient temperature, but by each individual leaf and it's detection of the photo period.
> Chad Schroter
> Los Gatos CA Zone 9
> >From: Donald Eaves <donald@...>
> >To: email@example.com
> >Sent: Tuesday, November 1, 2011 5:58 PM
> >Subject: [iris-photos] HYB: seed germination
> >The several hundred seedlings that sprouted and normally would have been
> >lined out remain in the seedling pots. Can't dig here without water. Those
> >seeds had the best germination of any seeds I've ever planted, percentage
> >wise. They are also having the best subsequent fall - or late - germination
> >I've ever had. I'm now looking at hundreds of the little fellows that may
> >spend their entire life stuck in a pot. I'm convinced now that germination
> >isn't entirely tied to temps. Germination came to a complete halt in April
> >when the temps got consistantly warm, but the fall germination started at
> >the end of
> >Augst when the temps were consistantly warmer than when they shut off. I
> >think the seeds must track the trend of the ongoing temps, which is not
> >quite the same as being dependent on the actual temp. That means they shut
> >down when the temps are continually rising, but reactivate when those temps
> >start going lower. Otherwise they wouldn't be starting so early. In any
> >case, a month or so ago when I counted there were nearly 70 new plants, so
> >I'm probably close or past a hundred or so now. They keep coming. The
> >photo is of a cross where there was only one seedling at the end of spring
> >and now has twelve in the fall, the newest showing up today. Seen a lot of
> >that this fall in the pots. Seven pods that had no germination at all now
> >have seedlings. I really wish now I hadn't dragged out any of the stored
> >seeds and planted them. I'm not at all sure even with some rain and
> >moisture I'll be able to manage the number of seedlings I have.
> >Donald Eaves
> >Texas drought zone, USA