Hi, this is Kimberly from landscape-solutions-for-you. This is a good question that has come up before. Petunias, like other plant specimens need soil to get their roots established and stay healthy. I would recommend to use your natural ground soil, top soil, or potting soil if you are putting the Petunias in containers. You can use the mulch as a finishing touch to a ground garden or containers. Mulch doesn't have the right nutirents to allow root growth. I hope this answers your question. Please feel free to ask others questions, and thank you very much for taking the time to inquire about your Petunias.
