Hyssop is a low growing evergreen, bushy herb growing 1 to 2 feet high, cultivated for its flower-tops, from which the fragrance is extracted. The herb grows in arid climates out of rocky soil and out of cracks in ancient walls such as in the old Temple area of Jerusalem. Hyssop was once called a "Holy Herb" because it was used for sprinkling in the ritual practices of the Hebrews. Ex 12:22 reads “And ye shall take a bunch of hyssop, and dip it in the blood that is in the basin, and strike the lintel and the two side posts..” Because of the reference found in Num. 19:6 (“And the priest shall take cedar wood, and hyssop, and scarlet, and cast it into the midst of the burning of the heifer”), we have called this fragrance “HOLY FIRE”. Hyssop, a very "clean, fresh" scent, speaks of spiritual cleansing by the refining fire of the Holy Spirit.
Ps 51:7 “Purge me with hyssop, and I shall be clean: wash me, and I shall be whiter than snow.”