Two forms of this Mediterranean native are commonly grown. One is a perennial, popular for its licorice-flavored seeds and young leaves; the other is grown as an annual for its edible leaf bases.
The plain species is a perennial (Zones US, MS, LS, CS; USDA 6-9) reaching 35 ft. tall, about 112 ft. wide, with finely cut yellow-green leaves and flat clusters of yellow flowers. Looks much like dill (Anethum graveolens) but is coarser in texture. Sow in light, well-drained soil; thin seedlings to 1 ft. apart. Use seeds of either type to flavor baked goods; use leaves as a garnish for salads, fish. New stems grow in spring from the perennial root. Bronze fennel ('Purpurascens', 'Smokey') grows to 6 ft. tall and has bronzy purple foliage; it is handsome enough to be grown as an ornamental. Fennel self-sows abundantly, unless you remove the flower heads.
F. v. azoricum, called Florence fennel or finocchio, is grown as a summer annual in Zones US, MS, LS, CS, TS; USDA 6-11. Lower growing than the species (to 2 ft.), with larger, thicker leafstalk bases that are used as a vegetable to be eaten cooked or raw. Remove flower buds before they open to encourage larger bulbs. 'Orion' forms especially thick, flavorful bulbs.
Don't reach for the bug killer if you see large, black-and-green caterpillars munching on your fennel plants. These are the larvae of beautiful swallowtail butterfliesso let them have a plant or two. Fennel blossoms' pollen and nectar also feed many beneficial insects, such as lacewings, ladybugs, hover flies, and soldier beetles.