
Certified GKH Gardening Expert
Over a few months they can break down, but they will not be an immediate fertilizer.
Once composted, they will be prepared for use. It will not harm your roses, but it will be a slow way to release potassium, calcium, and other nutrients to your flowers.
Here are some articles that will help:
https://www.gardeningknowhow.com/composting/ingredients/banana-peels-compost.htm
https://www.gardeningknowhow.com/special/organic/the-importance-of-soil-for-an-organic-garden.htm
https://www.gardeningknowhow.com/ornamental/flowers/roses/rose-fertilizer.htm