The area where the containers will be gets some morning sun & is mostly in the shade in the afternoon. Will we have to mulch the containers over the winter?
These should grow beautifully in your area. They do need lots of moisture, so be sure they're watered at least a couple times a week, especially if they're containerized. Yes, you'll want to add compost or other mulch over the winter. This is a great article that will tell you all about how to care for them: https://www.gardeningknowhow.com/ornamental/flowers/cardinal-flower/growing-cardinal-flowers.htm