I keep this plant in my small sunroom late Fall until May. Zone 5. Flowering this year for the first time! When I bring it in for the winter, I would like to prune it to a more manageable size. Would this decrease flowering next year? Also, not sure when it may need a larger pot? Thank you!
Generally, once the flowers drop it will be time to prune it. You can prune to your desired height. As far as when it needs a larger pot- You will know when roots start coming out of the bottom holes, and circling inside of the pot.
Here are some articles that will help:
https://www.gardeningknowhow.com/ornamental/flowers/iochroma/iochroma-plant-care.htm
https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm