How to make a homemade reed diffuser

I have purchased Reed Diffusers in the past and love the aroma from them. but they seem to evaporate so fast. Is it possible to make my own aromas? I checked bottles of  Lavender, Spearmint, etc at a health food store, but they didn’t seem to know of a recipe to use it.  Do you?  Also where is the best place to purchase them.? I thought the price was a bit expensive at the health food store.