Welcome to the Bunnings Workshop community @Dan79. Many thanks for your question, I'd be happy to answer it.
It's great to have you join us and fantastic to hear about your renovating project. As mentioned in the video by MaxPro that I've embedded below, the pebble resurfacer is suitable to be laid directly over soil substrates.
We look forward to hearing more about your outdoor garden renovation project and would encourage you to share any progress with the community as I trust many would like to follow along.
Please let me know if you need further assistance or have any other questions.