How to Grow the Fennel Plant (Foeniculum vulgare)

by Emily Nickles

The Greek nicknamed this memory-enhancing, cancer-inhibiting herb maratho, or “marathon,” based on its versatile uses—specifically to support longevity and strength. Fennel is a common plant that thrives particularly well in the Mediterranean and some areas of North America, Asia and Europe. It is used as both an herb, due to its medicinal properties, and as a vegetable, which can be eaten raw, stewed, grilled, baked or boiled. All parts of the plant are edible, including the seeds, roots, shoots, leaves, and bulbs. You’ll find it used in many dishes, as well as in salads. It is also sometimes called common fennel or sweet fennel.

According to the USDA National Nutrient Database, fennel is a significant source of vitamins A and K, phosphorus, sodium, potassium, and calcium. Fennel also contains small amounts of folate, which is known to inhibit cancer growth and protect from free radical damage. A recent study, examining the many benefits of fennel, notes that it is suited for pharmacological use and successfully treats over 40 types of disorders due to its phytochemical properties. Flavonoids, phenolic compounds, fatty acids, and amino acids compose the internal structure of this herb.

Growing Conditions for Fennel

Fennel is considered either a perennial or annual herb, depending on the region where you live. It grows best in temperatures that range between 21-24 degrees Celsius or low- to mid-70 degrees Fahrenheit. Early fall or late spring, after the final frost, are ideal times of year to plant fennel.

Despite its sensitivity to temperature, fennel can tolerate a wide range of soil pH, from 4.8 to 8.2. Fennel prefers well-draining soil that is rich in nutrients. If the soil is too dry, the bulb will bolt, or split. It should be planted in an area where there is plenty of room to space out the seeds that will allow six hours of full sunlight per day.

How to Plant Fennel

Most gardeners propagate this herb from seed, though you can purchase it potted and transplant to your garden. However, the University of Illinois Extension suggests that fennel does not transplant well due to its taproot system. Plant fennel or sow seeds in full sun in well-drained soil. Fennel enjoys rich, loamy soil such as soil with added compost or other organic matter. Each plant needs a depth of at least one foot for the roots to grow if you choose to use pots or other containers, so they must be large enough.

The seeds self-sow easily, and plants often return every year on their own. Initially, seeds should be planted 12-18 inches apart in rows 24 inches apart. The plant can grow up to 6 feet tall and 2 feet wide, so it’s important that there is plenty of space for each seedling to grow.

Care of Fennel

It is imperative that the soil remain consistently moist. The best way to test the soil is by pressing your thumb or forefinger into the ground about an inch deep, and checking to see how dry it is. If the soil is too dry, the stalks will split.

To create a bushier fennel plant, trim the stalks closest to the ground. New and more numerous shoots should then grow. You might have noticed the foliage looks similar to dill. You should keep it away from dill plants, as they will cross-pollinate, which creates and undesirable flavor in the seeds if you collect seeds to replant the following year.

Garden Pests and Diseases of Fennel

Common pests that interfere with the health and growth of fennel include the following.

• Aphids
• Thrips
• Larvae of anise swallowtail butterflies and other caterpillars for which fennel is a favored host
• Slugs and snails

Common diseases that can infect fennel plants include the following.

• Cercospora leaf spot
• Powdery mildew
• Mycoplasma
• Collar rot
• Root rot

Harvesting Fennel

Fennel is ready to harvest just before its flowers bloom—typically three to four months after planting. It can need up to seven months for the base to swell enough to be ready to harvest and eat, though the foliage and stems can be harvested at any time. The stems can be eaten like celery. To preserve the fennel seeds, allow them to dry until the plant has turned a golden yellow, and then empty the pods.

Fennel Varieties to Grow in Your Garden

There are two main types of fennel varieties.

1. Foeniculum vulgare, “herb fennel”
2. Foeniculum dulce, “Florence fennel”

Both fennel breeds share the signature sweet, black-licorice scent and flavor that resembles that of the spice anise. Herb fennel is used more frequently for medicinal purposes, while Florence fennel is traditionally used for cooking such as in soups and stews. Most people prefer the white, fleshy bulb that the Florence fennel is known for, though it is harder to maintain. Bronze fennel has darker colored purple-copper colored foliage, but is just as edible as the other color you’re used to.

Want to Learn More About Growing Fennel?

Writer Emily Nickles is a freelance writer and recent honors alumna of Texas Woman’s University. She was Editor-in-Chief of the student newspaper, The Lasso, for a year and was a page editor and reporter for three. Her senior year, Emily won the Sarah McIntire Award for Outstanding Capstone for her project titled The Lasso: A brief history 1914-2017.