In winter perennials are dormant which means that most plants will have no or very few leaves although if they are described as ‘evergreen’ they will have some leaves. Don’t worry perennials with no leaves during the winter will have plenty of roots to sustain them during this cold period.
What should the roots look like?
This depends on when the plant is potted. Most perennials are potted into 9cm pots before the end of July so that the roots will established in time for the cold winter months. The roots of different perennials grow at different rates. This depends on the variety; some establish quicker than others and therefore will produce abundant roots (for instance many hardy geraniums) while others are slower and the roots may appear sparse (for instance astrantia).
One point to remember, roots poking out of the bottom of the pot are not always an indication of a plant being pot bound. Some perennials go so quickly the roots can fill a pot within a few weeks.