How large is the plastic grower's pot? When I do this, I just invert another plastic grower's/nursery pot inside the decorative container and rest the planted pot on top. I try to scale the size of the growing pot to fit pretty closely to the decorative pot diameter, so it looks like it is actually planted in the decorative one. But for long term plantings I tend to plant directly into the larger glazed pot - most of my trees are planted like this and they do get moved around......a lot :-)) It's a bit of an effort but very doable and I am getting to be a old thing!!

In my climate there is little concern about heat or cold damage to anything grown in a container with a few minor exceptions. A lot depends on what you are growing but a zone 7 shouldn't pose many concerns. And a pot-in-pot planting will afford a greater degree of insulation than just direct container planting.