Dogfennel is a perennial weed with finely-dissected leaves.  Leaves are very aromatic when crushed.  Stems are erect, reaching 6 feet in height with a woody base. Flowers are small, greenish-white and borne in large flower heads at the tops of the stems.  Seed spread by wind so it is important to prevent plants from flowering in and around the nursery.  Seedlings emerge from spring through early autumn.  Plants are difficult to remove from containers.  If not removed completely with hand weeding, plants will re-sprout from broken stems.   Dogfennel is controlled from seed by many broad-spectrum preemergence herbicides.