How to Grow Fennel

fennel growing in a container

The Spruce / Michelle Becker

Fennel (Foeniculum vulgare) can be classified as both an herb or a vegetable, and it can be used in many ways in the kitchen. It's also a popular plant among herbalists and has been used for thousands of years as a natural remedy, most commonly for digestive problems. It has a wonderful anise flavor that works well in both savory and sweet recipes. The bulbs are commonly roasted or grilled or added, raw, to salads, and the feathery fronds can be added to salads and soups to impart a more delicate flavor.

There are two types of fennel that you may want to grow in your garden, depending on how you plan to use it. "Florence Fennel" (Foeniculum vulgare var. azoricum) is used more like a vegetable and is grown for its bulbous stem. "Herb fennel" doesn't produce much of a bulb, and it is typically grown for its foliage and used as an herb.

Fennel is sometimes grown as an informal ornamental plant, such as in border plantings in meadows or cottage gardens, where the feathery, yellow-green foliage and tall stature are attractive. It is also a good choice for butterfly gardens, as swallowtail caterpillars use it as a food source and pupal site.

Fennel is typically planted in the spring either from seeds or nursery starts. Bulbous types will produce edible bulbs about 80 days after planting the seeds. In warmer climates, gardeners may be able to grow two crops yearly, one planted in the spring for midsummer, then another for late fall harvest. The plant is often perennial in warmer climates, but northern gardeners must grow it as annual.

Botanical Name Foeniculum vulgare
Common Name Fennel, common fennel, sweet fennel
Plant Type Perennial herb, usually grown as annual
Size 4–6 feet tall; 18-36 inches wide
Sun Exposure Full sun
Soil Type Rich, moist, well-drained soil
Soil pH 5.5–6.8 (acidic)
Hardiness Zones 4–9 (USDA)
Native Area Mediterranean
fennel

The Spruce / Michelle Becker

closeup of fennel

The Spruce / Michelle Becker

fennel ready for harvest

The Spruce / Michelle Becker

harvested fennel

The Spruce / Michelle Becker

How to Plant Fennel

Though it is a perennial plant, fennel must be grown as an annual if winter temperatures in your area regularly fall below 15 degrees Fahrenheit. Even in warmer climates, gardeners often prefer to grow it as an annual. Easy-to-grow, fennel should be planted in full sun, in fertile, well-drained soil.

Plant after all danger of frost has passed, with plants set 6 to 12 inches apart. Fennel should not be planted in the same area as dill or coriander because the plants may cross-pollinate easily—seed production will be reduced. Fennel self-sows easily, so it's likely that if you plant it once, you'll see fennel popping up in your garden each spring thereafter.

Fennel can grow up to 5 feet tall, depending on which variety you're growing. Be sure to take its eventual size into account at planting time so it doesn't shade the rest of your vegetables. Also, it can inhibit the growth of tomatoes and beans, so avoid planting them near either of those crops.

Fennel Care

Light

This plant prefers full sunlight. Shady conditions will make it leggy and floppy. A minimum of six hours of sun is needed.

Soil

Plant fennel in moist, fertile, well-drained soil. It prefers acidic soil (pH 5.5 to 6.8). Amending the soil with plenty of aged compost is standard practice.

Water

Water deeply and regularly, but don't overwater or the plants will rot. A routine of providing 1 inch of water per week, combined rainfall and irrigation, is ideal.

Temperature and Humidity

Fennel does well in all climate conditions over its hardiness range, zones 4 to 9 and is perennial in zone 6 and south. It can be sensitive to cold and will need to grown as an annual in zones with frigid winters.

Fertilizer

Fennel does not demand feeding during the growing season, but the plants appreciate a layer of compost around the base every few months.

Fennel Varietes

Florence fennel (Foeniculum vulgare var. azoricum) is the type to grow if you want to harvest the bulbous stems to use as a vegetable. The leaves and seeds of this variety are also edible, so you get three uses in one plant. There are several cultivars of this variety:

  • 'Solaris' produces large semi-flat bulbs that are resistant to bolting.
  • 'Zefa fino' is ready for harvest in 80 days, bolt resistant, and very large.
  • 'Orion' is ready to harvest in 80 days and has large, thick, rounded bulbs with a crisp texture.

Herb fennel (Foeniculum vulgare) is the type to plant if you will use the plant strictly as an herb. There are two common varieties:

  • Green (Foeniculum vulgare 'Dulce')
  • Red (Foeniculum vulgare 'Rubrum')

Harvesting Fennel

You can harvest fennel leaves as needed for fresh use, and frequent harvesting will keep the plant producing. The seeds can be harvested when ripe, in late summer or early fall. The easiest way to harvest fennel seeds is to shake the seed heads over a sheet or tarp to collect the seeds. Let the seeds dry well before storing them in a cool, dark place.

Bulb-type (Florence) fennel can be harvested as soon as the base of the stem becomes swollen. Pull plants up as needed, and harvest any that are left in the ground at the end of the season before the first fall frost.

How to Grow Fennel From Seed

You can direct sow fennel seeds in your garden near your last spring frost date. Seeds should be planted 6 to 12 inches apart and 1/4 to 1/2 inch deep, and will germinate in 8 to 12 days. You can also sow the seeds indoors, under lights, about four weeks before your last frost date, then harden them off and transplant them into your garden.

How to Grow Fennel in Pots

You can easily grow fennel in containers, and this can be a good idea since the plant has a way of self-seeding and naturalizing somewhat too readily. Just be sure to plant in containers that are at least 10 inches deep.

Propagating Fennel

Fennel has a long taproot and thus doesn't divide very easily. The better method is to propagate by seeds. Seed heads can be collected, dried, and planted in the garden the following spring.

Common Pests and Diseases

Fennel rarely suffers from any serious problems, though caterpillars may eat at the tops of the plants. These are best handled simply by picking them off by hand. Most often, it is parsley worm caterpillars that are found, and these evolve into black swallowtail butterflies, known as good pollinators. You may, therefore, choose to ignore these green caterpillars with black and yellow bands. Aphids can sometimes be an issue, which can be treated by spraying with water to dislodge them. Avoid using any kind of pesticides or oils on edible herbs.