Q: I have three dwarf fruit trees: cherry, apricot, and nectarine, growing in large containers on my patio. They will be twelve feet high when mature. I would like to leave them outside for the winter but am concerned about the roots freezing.
A: Saving them will be trial and error on your part. An error might result in death for your fruit trees. Protecting the roots includes growing the plants in very large pots. Thirty to fifty gallon containers would be a good start, depending on the size of the tree. Foam containers offer more insulation than plastic or clay. You can wrap the pot with three inches of bubble wrap each winter as well.
Truthfully, a bigger factor to consider is the heating and freezing of the upper part of your trees during winter. If they are near a south-facing wall they will get hot during the day and will freeze at night. This will cause bark splitting and death. North and eastern exposures are best. Further, warm February temperatures will cause the trees to bloom early. A nighttime freeze will make all of the flowers drop, resulting in no fruit. Good luck!