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Re: [nafex] Re: chilling hours


I have read two different reasons for seed dormancy;

  * embryo finishes developing

  * chemicals inside the embryo need to break
    down to break dormancy

If I recall properly, IBA (rooting hormone) is present in the embryo, and
not until the IBA breaks down will the seed germinate.  Cold must help
break down the IBA.

So if you apply this to chilling hours...  (educated guess on my part)

If the same situation holds true for limbs of trees (they do not leaf out
in spring until IBA levels drop in the buds), then would GA3 (gibberelic
acid) help to break the limb dormancy (chilling hours)?

Would a spray or two of "tomato set" (GA3) help these under chilled
grafts to bud out?


Thomas Olenio
Ontario, Hardiness Zone 6a

On Tue, 12 Jun 2001, Ed & Pat Fackler wrote:

> Greetings folks:
>      My 2 cents worth on chill requirements of various fruit species.
> Some time around 20 years ago when I was stupid enough to believe all these
> written facts, I did some playing around with seed germination in an unheated
> basement and other situations.
>      After some few years of various types, based on what I saw at this
> constant 55 degree basement situation, the following observations were noted.
>      1.  Chill time does accumulate at this temperature, but the accumulation
> is much slower to occur (than the written "fact" stated).  Or, the implication
> from this was that so-called "hours or time" is coupled or dependant on
> relative temperatures during this period.
>      2.  Subsequent growth appeared to be somewhat slower or the seedlings did
> not exhibit normal vigor until the 2nd year in a nursery.
>      3.  One fact was substantiated or appeared to be anyway.  That was that no
> chill time accumulates at temperatures below 32 degrees or seeds simply are
> suspended indefinately.  I put some in a freezer with a constant temp. of
> zero.  I took them out a year later, stratified and most germinated.
>      Or, to quote the late Dr. Bob Lamb of Cornell, "the more I learn of these
> facts, the less sure I am of them".
> Ed, So. Indiana
> del stubbs wrote:
> > I dont know how to figure chilling hours ....we certainly had 4 months
> > completely below freezing, much below 0. I'd say an absolute minimum would
> > be 3000 hours below freezing and probably a lot more. I'll call around and
> > see if there is actually some gov. agency that actually records such info.?
> > any idea where to learn the chill req. of manchurian apricot?  Mn. Del
> >
> > >From: "Kieran or Donna" <redherring@tnaccess.com>
> >
> > >The chilling hour clocks on stone fruits tick only between 34 and 45
> > >degrees
> > >(anyone want to fine tune my numbers, which are from memory).  Your trees
> > >might have clicked off some of the time, but then you got them warm.  they
> > >stopped ticking.  They're like apple trees I have heard of in Florida that
> > >went dormant, stayed bare a whole summer, and leafed out the following
> > >spring.  Apricots in general have short chilling requirements, that is why
> > >they do so badly for us with our mild southern winters.  They're likely to
> > >bloom in Febuary here.   You may indeed have to chill your trees to get
> > >them
> > >to come out.  Maybe a block of ice wrapped up with the pots would do the
> > >job.  How many hours in a week?  What do apricots generally need?  500-600
> > >hours?   Do you think you got half that much before you brought them in?
> > >Donna in TN
> > >
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