I really am still trying to figure this cold frame out, thanks for the follow up - this year's been so warm,I'm afraid I've done more harm than good with it.
B
It isnt and doesnt need to be complicated.
I put my trees in my cold frame in the late fall/early winter when temperatures threaten to drop below 30ish. I might start getting the deciduous ones a bit ealrier (35sih).
But I leave the cover of the cold frame open so they hare at ambient temperatures until we get forecast to drop below 30. You dont cover it until you need to.
I also dont mulch my trees. My trees are packed in there pretty tight and my cold frame is made with walls of concrete block against the north side of my house. Its has a fence on either side of the short ends and the outside long end is cinderblock as I said and I park my boat in there for the winter so there is plenty of wind protection for them. I only cover it when temps are supposed to go below 30 or we have strong winds with wind chills below 25.
Picutres below are from the original constriction (not finished) and when I was doing an expansion and adding a section for taller trees,
The short section is 3 blocks high, the tall section is 4 blocks high