Dormancy

[Andy D]

Ive got 2 japanese maples, a japanese juniper, and a young transplanted maple and oak (separate of course!) and I was wondering when I should start their journey to fall and winter dormancy. Since I'm in Minnesota, I'm building and unheated woodframed polyethylene terrarium like thing to protect them from the wind and keep them at a somewhat consistent low temperature so the roots don't freeze. When should I put them in? also is it a good idea to surround the trays of the trees with mulch for unsulation?

[Gnome]

Andy,

I was wondering when I should start their journey to fall and winter dormancy.

If the trees are outside, as they should be, they already have begun the process of dormancy. I say process because trees begin to prepare for winter months before cold weather. The main trigger is the shortening of days that starts at summer solstice.

When should I put them in?

No rush to get things into the cold frame, allow your hardy trees to experience the early frosts where they are. This is also important. I leave my hardy trees exposed well into November, usually until around Thanksgiving.

and a young transplanted maple and oak

How recently were the transplanted ones moved? They may be a problem as tender, new roots will be more easily damaged than established mature roots. Make sure to locate the cold frame out of direct sunlight so the temperature inside does not vary excessively.

https://www.evergreengardenworks.com/overwint.htm

Norm