For this recipe you can use either a single herb or a mix of them. A sachet of rue is reputed to keep fleas out of a dog’s bed. Dry plants for sachets in the same way as flowers for dry potpourri.
Six ounces dried insect-repelling herbs (lavender, tansy, rue, lavender cotton, rosemary, most mints) half ounce ground orrisroot, half ounce ground spice: cloves, cinnamon,coriander.
Grind the dried herbs almost to a powder in a blender or food processor or with a mortar and pestle. Then mix in the orrisroot and spice. Before putting the mixture into bags, store it in a sealed jar for a day or two, to let any liquid be reabsorbed and to let the scents blend.
Flowers for dry potpourri: Pick flowers in the morning after the dew has dried. Pick fresh flowers. Petals for a dry potpourri or for sachets should be dried until they are crisp. Select a warm, dry spot, out of sunlight. Spread the petals in a single layer on newspapers. Shift the petals every couple of days to hasten drying. It may take two weeks for them to dry completely. Store them in a tightly sealed jar until you have enough to make the potpourri or sachet.
from: Magic and Medicine of Plants: Reader’s Digest.