There are two different types of fennel. Both forms sport feathery foliage, similar to dill leaves, and have a pronounced anise or licorice flavor. The type grown as an herb—common fennel—features finely textured foliage that reaches 3 to 5 feet tall. Stems, leaves, and seeds from common fennel are harvested for use in culinary dishes. Florence fennel—the second type—is grown like a bulb-type vegetable. Shorter than common fennel, Florence fennel has dark green foliage and develops a large, flat rosette of stems at the base of the plant. This cluster of stems is often called a fennel bulb.
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Where to Plant Fennel
Fennel looks at home throughout the landscape. Add fennel to the herb garden where it contributes an airy texture. Use it in the perennial garden as a soft green backdrop. Plant it in the vegetable garden for a quick-and-easy harvest. Wherever it grows, fennel attracts a host of beneficial insects and pollinators. Plant a few extra to ensure there will be enough deliciousness for both you and them.
Fennel, like most herbs and vegetables, grows best in full sun. It produces dense, abundant foliage when it gets at least eight hours of direct sunlight a day. When grown in part sun, it gets floppy and develops a loose habit. Fennel needs loose, fertile, well-drained soil to thrive. If your soil is exceptionally sandy or poorly drained, plant fennel in a raised bed filled with quality topsoil. Florence fennel is especially sensitive to soil moisture and thrives when kept consistently moist, but not wet.
Fennel grows best from seeds planted directly in the garden. The plant forms a long taproot that makes it hard to transplant. Sow herb fennel in the garden in spring after the chance of frost has passed. Begin harvesting herb fennel as soon as leaves are several inches tall.
Plant Florence fennel in midsummer so it can mature during the cool, short days of fall. Water the seeds well and continue to water the plants regularly to maintain a moist planting bed. Spread a layer of fine mulch around seedlings to prevent moisture loss.
Florence fennel is a heavy feeder. Fertilize plants every two to three weeks with a high nitrogen fertilizer, such as fish emulsion. When bulbs (another name for the stem bases) are full and plump, cut them off at soil level. Choose bulbs that are 2 to 3 inches in diameter, because larger ones are tough and inedible. Trim the feathery leaves down to the solid base.
Neither fennel type experiences much in the way of insect or disease problems. The caterpillars of swallowtail butterflies may nibble the leaves. Poorly drained soil may lead to stem or root rot.
More Varieties of Fennel
Foeniculum vulgare 'Purpureum', or 'Bronze', is a colorful version of standard fennel. It has licoricelike flavor and bronze-color foliage, and it grows 4 to 5 feet tall and 2 feet wide. In late summer, yellow flowers develop; if left to mature, the flowers produce edible seeds. Zones 4-9