Farmers' markets in regions that have four seasons are, as you'd expect, different in character than those you find in tropical climates. Harvest is seasonal, so the best times to visit them is during the summer and early fall. Many Farmers' markets in North America are only open during the summer months, shuttering for the winter.
Those markets that are open all year round need to adapt to the changes in the season. Most will be in an enclosed building which can be heated when needed (and which keeps you dry and cool in the summer, too). The local produce in the winter season is much more limited and includes produce and vegetables that stores well (eg. apples, potatoes, onions) or come from local greenhouses (peppers, tomatoes, mushrooms). But even on a cold winter day people like to go to the markets for great fresh meat and sausages, cheeses, and generally a large food court. Food courts in markets, in my experience, tend to be unusually good as they are an important crowd draw.
I visited the Farmer's market near my home in Calgary a few weeks ago. It was a good time to go as fresh crops were being harvested from the prairies and lots of fresh fruit was making its way to market from nearby British Columbia (well known for its fruit and wine). I thought I'd share that experience with you in this photo essay: