Very sad news, thank you for helping others on here, Vance. My knowledge of Mugo is better because you took the time to share your knowledge. Rest in peace.
I'm hoping to make this a decent tree before I jog on.. A Sango Kaku my dad bought me in a garden centre getting on for 20 years ago now. Not with us any more so it has sentimental value too. A pity about your dig, Jelle, it looked a beast.
I live in Yorkshire and it rarely hits -10C, usually a few around the -5C mark. Putting your trees in a heated greenhouse, by the house wall or on the ground creates a warmer micro climate.
The only trees I've lost to cold were in the bad freeze of 2010 when it dropped to a silly -15C for two...
I developed mine from small, pole like material that I've tried to air layer multiple times prior to chopping. My advice is to root graft, I know they take to grafting OK because I thread grafted a back branch on this no problem at all.
I'd take it back tbh - maybe have a look at the roots to see if it has vine weevil (very possible if it is in inorganic soil.) Obviously, reduce watering as it is not transpiring.
This Amur Maple shutting down early this year with some pretty colours. It's another year of trunk building to make a sort of multi trunk design in the end. Well worth a spot on the bench just for the Autumn show.
As dug & chopped
More pics, some refinement shots
Left pad thinned
It was really dense...
Light and air can now penetrate
Apex thinned, tried to make the mini pads smaller the higher up I went
Tree fully thinned and a little wire added
From a 2 leafed seedling I collected on a grass verge. It's taken 31 years with many of those bombing away in the ground. Wooden board then tiles used for nebari development. In training for 7 or 8 seasons now to hang a branch structure on it.
I think you should let it grow for a season or two, the extension growth should be 3 or 4 inches with a healthy tree. Get it growing stronger and it'll develop faster.