Treating frost damage in subtropical trees

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