Steve,

I'm sure Michael will respond as to which he was recommending.

I would like to comment on your question, though:

As you said the co-poly would warm the mulch during the day but the shed
or garage would provide some insulation from the cold ground.

It isn't the cold ground that your trees need protection from, it is the
cold air. The ground stays at a relatively even temperature, which is quite
a bit warmer than the air temperature, especially as one goes below the
surface a bit. Putting your trees on the ground and mulching around them
helps to connect them with the ground and keep their rootballs at ground
temperature. Roots are designed to live at ground temperature, not at the
much colder and widely fluctuating air temperature.

Regards,
Roger Snipes
Spokane, WA. Zone 5-ish

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