Fennel (Foeniculum vulgare) is a fragrant herb and vegetable known for its distinctive anise-like flavor. Whether it behaves as a perennial depends entirely on the specific variety grown and the local climate. Some varieties are cultivated for their feathery leaves and aromatic seeds, while others are grown for their crisp, enlarged stem base, often called a bulb. Understanding the life cycle of these two main types is necessary for successful cultivation.
Understanding Fennel’s Life Cycle
Common or Wild Fennel (Foeniculum vulgare var. vulgare) is typically a short-lived perennial or biennial in mild regions (USDA Hardiness Zones 6 through 10). A biennial plant grows foliage in the first year, then flowers, sets seed, and dies in the second year. In warmer climates where the roots do not freeze, common fennel can persist for several years, behaving as a true perennial.
Florence Fennel, also known as Finocchio or Bulb Fennel (Foeniculum vulgare var. azoricum), is botanically a biennial but is almost always cultivated as an annual vegetable. This variety is grown for its swollen, edible base, which forms from overlapping leaf sheaths. Since the goal is to harvest this “bulb” before the plant flowers, its life cycle is intentionally cut short in the first year. If left unharvested, Florence fennel may survive the winter to flower in its second year, but the quality of the edible bulb will be ruined.
Essential Growing Conditions
Successful cultivation requires full sun, meaning a minimum of six hours of direct sunlight daily. The plant thrives in well-drained, moderately rich soil with a pH range between 5.5 and 8.0. Soil that is too rich in nitrogen, however, can result in bland-tasting bulbs and foliage.
Consistent moisture is important for Florence fennel to ensure the base develops properly without splitting or bolting. Fluctuations between dry and wet conditions stress the plant, causing it to prematurely send up a flower stalk that ruins the edible bulb. Common fennel is more tolerant of drought once established due to its deep taproot.
Fennel should be direct-sown into the garden bed after the last spring frost, or in mid-summer for a fall crop. The plant dislikes transplanting due to its sensitive taproot. Florence fennel bulbs are ready to harvest 80 to 100 days after planting.
Controlling Self-Seeding and Spread
The common variety of fennel tends to self-seed aggressively and can become invasive. This spread is compounded by its allelopathic properties, where the plant releases chemicals that inhibit the germination and growth of other plants. This chemical interference necessitates planting fennel away from sensitive garden vegetables, such as tomatoes, beans, and cilantro.
To manage the plant’s spread, the most effective strategy is deadheading, which involves removing the flat, yellow flower umbels before they set seed. Without this intervention, the plant will drop numerous seeds, leading to a much larger population the following season.
Removing established perennial fennel is challenging due to its deep taproot. Unwanted plants must be dug out completely, ensuring the entire taproot is removed to prevent resprouting. The allelopathic chemicals are short-lived, so the ground is typically safe to replant with other species the next growing season.