Although fennel (Foeniculum vulgare) is a hardy perennial it is usually grown as an annual. Fennel can grow up to 4 feet tall, producing feathery leaves with tiny yellow flowers in late summer or autumn. Fennel is grown for its seeds, stems, roots, and leaves, all of which are used in a variety of cuisines. Fennel enjoys cooler temperatures and lots of sunlight.
Plant the fennel seeds into peat pots about four to six weeks before the last expected hard frost in late winter or early spring. Sow the fennel seeds about ¼-inch deep in the peat pots.
Place the fennel-sown peat pots in a dark place while they germinate, which usually takes about 10 to 14 days. Maintain air and soil temperatures of about 65 degrees F for the fennel seeds.
Sprinkle the peat pots lightly with water once every two to three days while the seeds are germinating to keep them moist. After the fennel seeds begin to sprout, move the peat pots to a bright, sunny window.
Continue to water the fennel seedlings to keep the peat pots evenly moistened. Transplant the fennel seedlings outdoors in early spring while the soil is still cool but after the last hard frost, and when the seedlings are about 3 to 4 inches tall.
Plant the fennel seedlings in their peat pots directly into the soil, spacing the plants about 10 to 12 inches apart in rows that are about 36 inches apart. Choose a planting location that's in full sunlight and has some protection from high winds.
Water your fennel herbs to evenly moisten at least the top 6 inches of soil two or three times per week to supplement rainfall, allowing the soil to dry out slightly before watering. Pinch off the flower heads after they're finished blooming to encourage more leaf growth on the fennel plants.
Harvest your fennel in autumn by cutting the entire plants, snipping the stems back to the ground. Place the fennel herbs upside-down in paper bags and allow the seeds to dry.