Ok. Seems unnecessary at best, but maybe I’m missing something. What are the benefits to repotting spruce at the end of summer that outweigh the benefits of repotting in the spring? Just if you have too many repots in the spring to do? What about substantial root reduction? I don’t own a greenhouse, I can’t protect my trees in the winter the way that some people can. No way am I going to do major root work going into my upstate NY winter. Would surely hurt the cold hardiness of the tree. I guess I just don’t see the point of repotting at that time, but I must be missing something.
Trial and Error is how I came to August repotting. The initial trials and errors were with JBP, and the unique quirks of my climate. JBP
need at least a week or two of temperatures above 80 F to really wake up in spring. Living in the ''Lake Effect" zone of Lake Michigan, there are years I don't repeated temperatures above 80 F until almost July. JBP repotted after last frost but before bud growth and extension showed in May and June often died on me. That is when I began repotting JBP in August, and my high mortality rate dropped from nearly 75% to less than 10%. This is where I really began to embrace late season repotting. Now when I post I usually don't comment on JBP, because I have not had much success with them, even though I have always had a few over the last 35 years. I consider others more expert than I and just quietly do my thing with my JBP.
But expanding on the success with JBP, tried with other trees, and generally across the board for conifers and ginkgo, I have had very good success with August repotting. I also have better success with Chaenomeles and Diospyros repotting in September. (flowering quince & persimmon). Both you will find Japanese references stating ''autumn'' repotting is best.
Yes, in many cases spring and late summer repotting are nearly equal in success. Larch is the only conifer I have found to do better for me with spring repotting.
Lastly - you are partially correct, I have many demands on my time in spring. Being the weekday site manager for the property my cousin's & I refer to as our blueberry farm, I have very little free time in spring. Blueberry harvest comes to an abrupt halt for us about July 25, the week after July 25 we throw fertilizer around, then take August off to recover. So yes, I have time in August I don't have in May, June or July. The only crop on the 76 acre property is 3 acres of blueberries, the rest is open fields or woodlot. A more accurate term than ''Farm'' would be hunting camp. But the blueberries are my project, and the 3 acres actually produced enough that they covered the mortgage, taxes and insurance for the whole 76 acres. They did not cover any equipment, fertilizer, bug spray or labor. But this is ''a start''.
So the demands on my time forced me into widening the scope of species I repot in August-September. I have done enough spring versus August-September that for some species like Mugo, Jack pine, persimmon, flowering quince, and most other conifers that I do recommend August-Sept. Because of my unique climate, I don't usually tell someone when to repot JBP, unless I think they too are in a long cool spring micro climate.
