A plant growth regulator (auxin or synthetic analogs) applied to cuttings to stimulate root initiation and improve propagation success rates.
Rooting hormone (usually a powder you dip cuttings into) contains plant hormones that trigger root development in cuttings. It speeds rooting and increases success rates. It's optional but helpful, especially for difficult-to-root plants. Hormone concentrations vary; follow label rates.
Rooting hormone improves propagation success, especially for woody plants and difficult-to-root species. It makes propagation easier and faster.