I grow a lot of perennials (as well as shrubs, vines, grasses and small trees) in containers on a pretty much permanent basis. Because growing anything in a container limits root run, I do think it prudent to at least root prune if not divide the perennials on a routine basis. Root disturbance with containerized perennials, if done carefully, is a good thing! And some simply do not thrive for more than a season or two in containers and these get transferred into the garden. Or tossed :-)

While I often refresh various containers each season - change out some plants or redo entirely - this activity can take place pretty much anytime. The majority are attended to in late winter or early spring as I am doing other perennial chores like dividing, transplanting or cutting back for the season. And I always refresh or replace the container soil at that time.

btw, if you select your container perennials with an eye primarily to foliage effect or a focus on being evergreen and combine them with small shrubs or trees, your containers can look as good throughout winter as they do in the growing season. This may not work well in every location, but should certainly be appropriate in a zone 7 situation :-) Look for plants like bergenia, heucheras, euphorbias, ferns and grasses. Also many groundcovers, wintergreen and hellebores make great year round additions for perennial containers with specific winter interest.

I'm a zone 5 rural gardener with mass flower and bulb beds, but I also plant many containers each season to decorate the place. I use a combination of annuals and perennials, and also keep a few trees in pots year round.

My personal preference is to wait until spring to do any major re-potting or root trimming. I wait until the possibility of frost is past. At that time, I refresh the medium in my patio pots, and plant them with the combinations that will decorate the yard and gardens for the season. I also bump any plants that need it to the next size pot, or trim the roots and refresh the soil.

Summer is simple maintenance... watering, feeding, trimming, etc...

When late summer/early fall arrives, I begin to break down the pots of annuals and perennials, and plant the perennials in the garden beds. Tender tropical plants get hauled to the basement or brought in, pot and all... shrubs and trees get moved to the garage, along with any perennials that will remain in the pots over winter. Annuals are pulled and composted, and any indoor plants that summered outdoors are brought back in.

I spend winter caring for my indoor plant collection, and dreaming up new combinations for the patio pots I'll plant the following spring. Spring is when I do the majority of my container gardening.

Thanks for the advice. Based on what people have said, and given my very limited space in the ground, I may try "rotating" my perennials. After dividing, I will put some that were in the ground into containers, and some that were in containers into the ground. Reading more on the forum, I am seeing the necessity to amend the soil each spring anyway so I will use that as my time to make the switch.
How does that sound?