I dry yarrow flowers . . . dry plantain . . . dry jewelweed. on an old screen in my greenhouse. . . all picked fresh and dried right away. . . . then I stuff a canning jar with 1/3 of each (guessed) leave a few empty inches at the top and fill the jar with olive oil. Then I set it aside for at least six weeks. I then strain the liquid and add warmed beeswax to my desired solidity. then I pour the finished product into small tins and store them in a cool dry root cellar. I use jewelweed because it has a reputation for healing poison ivy around here.
My weeds, plants, and mushrooms are all wild grown . . . I 'think' that makes a great difference in their strength. I'll be making a batch of dandelion flower salve in a couple of days.