Hello,
I just thought I would add my opinion. I am near Detroit, MI zone 6a. Most my trees are on MM111. Most of these are 10 years old and about 1/2 of them have burr knots. All of my trees are doing fine despite the burr knots. One thing I like about them is they get big enough that the lower branches can now be pruned above the browsing deer. My soil is a nice sandy loam, but only about 8-10 inches deep or so, then the clay is hard. When I first planted this orchard I figured mm111 was the most forgiving. The only problem is that my trees are very vigorous and I have to prune a lot. I prune in the winter and summer every year.
Also, some of my trees took a long time to come into bearing. I have 2 trees on mm106 and they are doing fine here too.
Good luck
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