Ask Mr. Smarty Plants

Any plant being grown in a container outside in Zone 5 is going to be a difficulty. Plants' root are ordinarily insulated by the Earth itself, both from heat and, certainly, from cold, as in your case. The only insulation your outdoor pot has would be a few inches of potting soil and a very thin container wall, whether it were pottery, plastic or stone. You are correct that your area in Duchess County is in Zone 5b, which means your average annual minimum temperature ranges from -15 to -10 deg. F. We don't have any way to rate cold resistance of plant roots, but we will bet there are not any that would go for those temperatures from such an exposed situation. The main problem with exposing plants to cold is that the water in those plants, especially that stored in the roots, would freeze, expand and rupture cell walls in the plant, resulting in death for the plant.

Please read our How-To Article on Container Gardening with Native Plants. Of course, down here in Texas we are more in fear of heat damaging container plants than cold, but the criteria for selecting pots are still valid. There are a number of trees and shrubs native to your area that would be just fine planted in the ground, but not in a pot. If you purchased a large pot, it would be a considerable expense, and the likelihood is high that you would have to replace the plant every year, also expensive.

Smaller pots that could be taken into a protected area, like a garage, seasonally could give you some outdoor color and form in warm weather, but that's about the best you could hope for. If you have a particularly attractive pot already, and it has drainage holes, you could plant blooming annuals every Spring and leave the pot empty as a decorative feature in the cold weather.