I love to use natural materials with the gelatin printmaking process.
The 2 prints on the right were made with real grasses and ferns. I love how the gelatin plate allows the printmaker to capture the delicate details of the natural material, and with mere hand pressure.
You can even use ferns and natural materials when printing on fabric with ink and the gelatin plate.
All grasses, leaves and ferns are not the same. You want to choose very flat materials with interesting shapes and textures.