I haven’t tried any of these last methods, but I’m intrigued by the fact that they’re all listed in a publication put out by North Dakota State University and the U.S. Department of Agriculture. Imagine, the U.S. Department of Agriculture has an opinion about good ways to preserve flowers and leaves!
Check out this publication on Methods of Preserving Flowers for instructions for sand drying, drying with silica gel, and microwave drying, and recipes for homemade drying agents including salt, cornmeal, pumice, and borax.
