Hi Al, I'd guess most of it comes from the building, but since there is a roof more of it gets trapped than it does on the north side. It may also get some heat coming up from the basement and garage below. The upper half of the building gets direct sun late morning and midday, but it doesn't get quite high enough to shine down onto the patio. I'd say it starts to clear the roof next door starting sometime in February, and things are thawed out completely by March in the east yard. North side took at least another month to get going last spring.

The safest course would be to provide some root protection for them. May not be necessary in most Z6a winters, but no harm in having it. As for where... Fully dormant plants do not need light, so that condition does not disqualify the crawl space. Watering should also not be necessary. Wrapping each pot with bubble wrap or another type of insulation then placing the pots close together in the barn, then wrapping the whole should be fine, too. Placing a large carton - I've used rigid styrofoam to make a "carton" big enough - over everything to capture some ground heat is frequently recommended but would not be relevant if there is no ground contact between the barn floor and the earth. You also want to be careful of mice and voles. Some years they do not present a problem, but last winter I found voles to be a major headache. Trapping is probably most effective.

Lou, I have often seen it suggested that the watering of the soil needs to be done a day or two prior to the freeze; that way the soil has a chance to absorb moisture but drain off enough to prevent a soggy condition that will create ice forming in the soil or in contact with the roots. Yes dry conditions are hard on plants and trees when they are encountering freezing temps, but the freezing time is not the best time to water: that is unless your soil temps are remaining well above freezing and if the soil also drains so well that there is not a risk of the water to freeze within the soil around the roots. Are you able to cover your containers and protect them from the coldest overnight temps; or even move them into the garage or other protected area where you could water them without the threat of the water freezing before the soil could become moistened from absorbing well the water. One other thing to consider is, are the items in your pots dormant already before the freeze hit, if not, do not water them, because the water your items take up; especially if the sap is still abundant in the trunks. These will generally experience the same conseqences of pipes which are frozen in a home. Once those frozen pipes are thawed too quickly they burst. Same thing happens to the trunks of young non-dormant trees and shrubs which freeze; sap expands quickly and breaks through the cell walls in the young trunks or stems. The plant taking up water just prior to freezing worsens this affect. Our local nurseries often encounter this problem in the early spring if temps have risen enough to encourage breaking of dormancy, and then often a sudden late freeze follows so quickly that the tree or shrub does not get the right amount of time and environment to once again drop it's sap's upward flow. Some local nurseries in my area have often lost many potted plant, trees and shrubs at such times.

In MN , zone 4 to 4.5. Gets about -20 to -25 at worst or best, depending on your outlook. I have the volunteers: maples of diff. varieties, black walnut, sumac, dogwood, poplar, juniper, pear and apple. Probably pretty hardy since they sprouted up on their own here. But I did pull them up this summer, not dig. The hostas and lillies in pots are not much concern to me as I left many fully exposed last winter with next to no mortality. The seedlings are: in order of most concern for survival: heptacodium miconioides - seven sons flowering tree from seed - zone 5 Bristlecone pine from bare root - zone 4 Eastern white pine from bare root - zone 3 Niobe weeping willow from cuttings. -zone 3