Re: Treating frost damage in subtropical trees

Mike,
Although we didn't really get cold enough here in
Berkeley this latest freeze to stress out Chorisia, I
do remember very similar effects on this tree from the
December 1990 freeze in my own garden.  Unfortunately
I lost my trees altogether from a suspected low of
24F.  Perhaps if I had left the tree stumps alone they
might have regenerated, but did not have the patience
to wait.  I can't say that I noticed a similar effect
on other subtropicals such as Jacaranda or Tabebuia
species.

I don't think we got much below 27~28F during this
freeze event, so damage was mostly cosmetic to most
plants.  In my own garden, various Plectranthus
species from South Africa were the worst effected, and
Aeoniums also took a bad hit.  The Crassula multicava
most recently featured in the latest NorCal Medit
Plants Bulletin is another sensitive succulent that
doesn't do well with frost.

I wonder if this problem with ongoing rotting of
nonfrozen Chorisia branches also occurs on older
trees?  I noticed that the large old Chorisia speciosa
at the Ruth Bancroft Garden was badly damaged in the
1990 freeze, and as recently as 2006, the last time I
again saw it, had recovered well, but with obvious
signs of where major branches had been completely
killed.  The main trunk itself seemed mostly
unaffected.  I am not sure how cold they got there in
this latest freeze, or if the Chorisia was again
impacted.  I think it would have been subjected to mid
teens F temperatures there in the December 1990
freeze.
--- Michael Mace <mikemace@att.net> wrote:

> Folks,
> 
> I'm a longtime lurker on the list, de-cloaking for a
> question.
> 
> I've been reading with interest all of the reports
> on the recent freeze in
> California.  I live there, and will be contributing
> a report on what died
> and didn't (once I get a chance to write it up).
> 
> But in the meantime, I wanted to share a thought
> about treating frost damage
> in subtropical trees.  I don't think I've seen it
> discussed here (my
> apologies if it was and I missed it).
> 
> The conventional wisdom is that you're supposed to
> wait until growth resumes
> in spring before doing any pruning of frost damage. 
> I'm sure that's correct
> in general, but in some types of trees I've had
> nasty experiences that make
> me think we should prune them a lot earlier.
> 
> I am raising several Chorisia speciosa
> ("Floss-Silk") trees in my backyard.
> They're finally getting pretty big (maybe 20 feet),
> but when they were
> saplings we had a couple of nasty freezes here that
> blackened the buds at
> the ends of the branches.  That's not a big deal in
> Chorisia speciosa -- it
> seems to have latent buds all over the place, and
> will re-sprout quickly
> when the weather warms.  So I left them alone and
> waited for spring.
> 
> One tree started to bud out just below the frost
> damage, but to my surprise
> the new buds died and the branches started turning
> black, creeping back
> along the branches toward the trunk.  On one tree,
> damage that had started
> just at the branch tips spread several feet back
> down into the trunk of the
> tree.  
> 
> Finally, in desperation, I cut off the trunk below
> the blackened area, about
> three feet above the ground.  It was left as a
> single stump, but the tree
> then merrily sprouted several new branches, one of
> which I trained into a
> new trunk.
> 
> Here's what seemed to have happened: the frost
> damage started some sort of
> dieback process or infection that the tree was
> powerless to heal.  It was
> like tree gangrene -- I had to cut off all the
> damaged wood, or the problem
> would just keep spreading.
> 
> Since then I've been careful to watch for frost
> damage in the subtropical
> trees I foolishly try to grow in my climate.  I've
> seen the same effect
> several times in Chorisia and relatives like Butea
> and Bombax.  
> 
> I suspect it can also happen in Brachychiton.
> 
> Has anyone else seen something similar happen?
> 
> If I'm right about this, we need to treat those
> trees differently after a
> bad frost: watch for damage, and be ready to trim it
> off as soon as it shows
> signs of propagating back from the branch tips. 
> That's hard to do on a big
> Chorisia tree, but at least you can do it on the
> younger ones.
> 
> Any thoughts or comments?
> 
> Mike
> San Jose, CA
> (zone 9, min temp 19F one morning last month)
> 
>
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index