Fennel, Foeniculum vulgare, is a short-lived perennial native to the Mediterranean area which has naturalized around the world. Because it freely reseeds itself, it is considered an invasive weed in the US and Australia. Fennel has been used for food and medicine since ancient times. It was used by both the Greeks and the Romans. It spread to Asia where it is an important ingredient in East Asian cuisines as well as an ingredient in the Chinese Five Spice Powder. It is one of the three herbs used in absinthe, originally a medicinal preparation which then became a popular alcoholic drink in the 19th century.
Fennel is often planted in butterfly gardens because it is the nectar plant of the swallowtail butterfly. This means that butterflies lay their eggs on the plants which then hatch into caterpillars which eat the plants. If you see damage on your plants, look for the green and black striped caterpillars which will morph into butterflies. I like to plant bronze fennel in my butterfly garden because of its wonderful bronze foliage.
There are three main types of fennel: sweet fennel, Foeniculum vulgare, bronze fennel, Foeniculum vulgare ‘Purpureum’, an ornamental fennel with bronze foliage and Florence fennel, Foeniculum vulgare Azoricum, which forms a bulb at the base of the stem that is eaten as a vegetable. In Italian it is called finocchio.
All three types of fennel taste similar to anise (Pimpinella anisum) although they are actually related to caraway (Carum carvi). Fennel, dill, caraway and anise are all members of the carrot family. Fennel has the characteristic umbel flowers of the carrot family. It looks like dill but with finer foliage. It will cross-pollinate with dill if planted too closely. The resulting plants will not taste like either parent.
Fennel needs full sun and well-drained soil. It has a long tap root making it a drought tolerant plant although in the wild it grows along riverbanks and near sea shores, as well as fields and other open areas. It is hardy in zones 4 through 9. Plants can grow to a height of 6 feet. They should be staked if grown in a windy location. Florence fennel is slightly shorter, growing to 4 feet.
Fennel is easily grown from seed. The seed should be direct sown in your garden rather than started indoors because it doesn’t transplant well due to its long tap root. Sweet fennel or bronze fennel seeds should be sown after all danger of frost has passed. Florence fennel seed should be sown mid-June to July depending on your growing zone to take advantage of the shorter days and cooler temperatures of late summer into fall. If sown earlier and grown during the hot days of summer, it will “bolt” or flower earlier which will have a negative effect on the flavor of the bulb. Germination for both types of seed is 12 to 18 days.
Sweet fennel should not be grown in rich soil or heavily fertilized. It should be grown in poor, well-drained soil for maximum taste. Florence fennel, which is grown for its bulb, should be planted in rich soil, well-fertilized and well watered. When the bulbs reach the size of an egg, you should begin to hill them up like you would leeks. This will give you whiter, more tender bulbs. The bulbs can be harvested when they reach the size of a tennis ball. Just dig them up, cut off the roots and stems and store in a cool place for up to three weeks.
Sweet fennel is grown for its foliage and seeds. The foliage can be harvested any time and used fresh or dried. To harvest seeds, allow the plants to flower and set seed. When the seed has turned brown, it is time to harvest it. I usually place a paper bag over the umbels, cut the stalks and allow the seeds to finish drying in the same paper bag. You can also wrap the umbels with cheesecloth, cut the stems and then place them in a paper bag to finish drying. The dried seeds should be stored in an airtight container, preferably glass. The container should be stored in a cool, dry, dark place.