Answer: Dwarf Alberta Spruce are among the hardiest of evergreens for containers, but the more you can insulate the roots, the better. Snow by the way is a good insulator, so it is not such a bad thing that you have snow at the same time as the cold. Wind protection is important because wind can be very drying to plants over the winter.
You might be able to heap mulch or wrap some insulating material such as bubble wrap around the pots to try to insulate them. You could also consider bringing the big containers inside to thaw so you could then plant and return them outside again. Also, sometimes the top crust of soil freezes and then a bit deeper the soil is not frozen, check to make sure this is not the case.
In terms of watering, there is no absolute schedule. The goal is to keep the soil evenly moist but not sopping wet at all times -- so that means keeping an eye on the soil moisture except when it is frozen. When the soil is frozen it will not absorb the water. How often you need to water will depend on the temperatures, the wind, the size of the plant in relation to the pot, the type of soil mix used, and so on. You just have to dig down a bit with your finger and see if and when you need to water.
Good luck with your trees!
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