Uli, yes, you can take pieces or rather sections of the large stem of tree Dahlias and lay them horizontally or vertically in the ground and they grow, most of the time. They also produce large tubers which can be planted. The Tree Dahlias in California where I am last several years, we cut them back and give away the sections for friends to start plants. Since you want a node or two on your starting piece, these sections are usually rather large, around a foot in length. Carolyn in Los Gatos, CA