North American Fruit Explorers mailing list at ibiblio

[Alan Haigh <alandhaigh@gmail.com>]

Stephen wrote, "My experiences matches what I've found in research - winter
pruning will
encourage water sprouts (and other growth); summer pruning will be more
effective."

More affective, how?   And what research?   I had the argument about
relative regrowth response of summer and winter pruning with Lee Reich last
year, only it was how winter and summer comparatively affect overall vigor.
I insisted that summer pruning was more de-invigorating than winter pruning
but Lee claimed that the research contradicted this.

When I found research that supported Lee's position I assumed it was because
the work dealt with trees on full-dwarfing rootstock.  It involved measuring
all shoot growth including watersprouts, and spring growth was about the
same whether pruning was done the preceding summer or winter.  There have
been several studies that reveal this.

I still believe that over time summer pruning has to be more deinvigorating
than dormant but recently I found a study of trees on semi-standard
rootstock that reacted the same ways as trees studied by Lee's man.  No one
has explained to me how removing wood that is harvesting energy for the
entire tree can be removed in summer and not slow the tree down more than
removing that wood after the energy harvest is done for the year.  My own
experience of summer pruning hundreds- more like thousands of trees,
sometimes exclusively summer pruning, anecdotally (but to my mind, very
clearly) indicates a reduction in overall vigor, but the water sprouts still
come back vigorously every season.

If you want to see some of the studies go to the International Horticultural
Society (IHS) site.