Experts and BHG readers answer.
PERENNIAL CONTAINER GARDENS
Thanks for writing. You may be able to overwinter a perennial container garden in your porch for the winter; it depends on how hardy the perennials are, what size the planter is, and how much protection your porch offers.
As a general rule, you'll want a container at least 36-48 inches in diameter and select perennials that are at least one Zone hardier than the Zone you garden in if you wish to keep perennials outdoors all winter in a pot.
Otherwise, you can dig a hole and "plant" the pot for the winter --- then in spring, just pull the pot out of the ground, wash it off, and your perennials should be fine.
---Justin, Senior Garden Editor, BHG.com