Plants in pots...above ground, in winter. Will roots be damaged ?
We are in Merlin 97532 and have a shaded, south facing wall with a 3 x 25 foot planting strip. Canna in summer. After I cut down the canna to the ground...I wanted to place 5 gal plastic pots or wood planters, with hardy ferns or shrubs...to cover up siding. The roots will be colder in the pots...than if in the ground. I find various USDA or Sunset Western Garden Book zones. Do I have to drop down a zone or two...to be sure the exposed root system will not be killed ? Many thanks....
If your local temperature goes into the mid 20's and persists for several days or longer, it will make just about any shrubs roots dieback. Most people don't realize how much protection the ground and a good mulch provides for plant roots. Once root dieback begins your plants will die a slow death. If you put ferns into the pots they probably will do fine even if the pots freeze.
If your site does not get that cold and only dips into the high 20's for short periods of time at night and warms back up during the day into the 30's, your plants in pots should be fine.
That is a good idea to follow the Sunset guide and if it says those plants can tolerate a zone 5 or 6, they should do fine in a pot in our zone 7 or 8.