North American Fruit Explorers mailing list at ibiblio

[Alan Haigh <alandhaigh@gmail.com>]

Steve wrote "I'm also curious, but not really worried, about how my trees will do
considering that November was warm and actually sunny but then last week
we went down to -25F one night."

 

I'm no authority as far as scientific evidence on the subject of hardening off but I have observed a few interesting occurrences regarding this issue.

 

I've often read of the danger of late fertilizing because it may spur on late tender growth and leave trees vulnerable and I think this fear is greatly overblown.  I've never seen a late spurt of growth caused by a late N application although I often do my own fertilization around mid-Sept, however, I have seen an impressive late spurt of growth brought on by a prolonged drought that ended with ample rain starting in mid- Aug.

 

In this instance the rain caused my nursery trees to really take off, especially the J. plums.  The damage that resulted following a relatively cold winter here in southeastern NY Z 6 was only a few dead tips- the actual late summer into fall growth on only the J. plums.  There was no other damage on other species and the J. plums seemed unaffected by the minor burning.

 

I have had difficulty zeroing in on  the cause of cambium kill when it occurs.  Maybe if I kept more thorough records I'd find a clue somewhere but last year I lost a few apricots on different sites I would have considered the most favorable while on sites that appear worse where I know winter and spring lows are lower there were no problems.  I can only guess that trees on better sites were further out of dormancy when a hard frost hit- it almost certainly wasn't winter cold as winter was mild without out of the ordinary fluctuations. 

 

It is red-fleshed J. plums (though not the tough Methely) that tend to suffer cambium damage and sometimes kill as well as the before mentioned apricots which I think is an indication that it is spring that is often the most hazardous time for this kind of damage in my area.  Still the damage is unpredictable for me as it doesn't seem to coincide with unusual fluctuations from warm to cold.