All About Growing Fennel

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Illustration by Keith Ward
Versatile fennel can make a soothing tea, an interesting licorice-flavored herb, or a crunchy, celery-like addition to main dishes.

(For details on growing many other vegetables and fruits, visit our Crop at a Glancecollection page.)

Fennel leads a triple-life as a vegetable, kitchen herb and medicinal herb. Varieties developed to produce crisp bulbs are easy to grow as cool-season vegetables. Young, garden-grown plants also provide tender fennel fronds and celery-like stems to chop into salads, grain dishes or fish dishes.

Fast to flower, all types of fennel produce hard, plump seeds that can be used as a spice, or brewed into a stomach-soothing tea often recommended for colicky babies. In addition, a half teaspoon of crushed fennel seeds included in the cooking water will reduce the gas-provoking compounds in cabbage, broccoli and onions.

Types of Fennel

Annual bulb fennel (Foeniculum vulgare var. azoricum), also calledfinocchio, is the crisp bulb vegetable with nutty anise flavor, hence the common name of anise fennel. In most climates, bulb fennel or finocchio can be grown twice a year, in spring and fall, on a growing and planting schedule similar to that of broccoli. Bulbs form about 80 days after seedlings are set out in the garden.

Perennial herb fennel (Foeniculum vulgare)is hardy toZone 4, and includes varieties blushed with bronze or purple, often called bronze fennel. Perennial fennel varieties with green foliage, such as ‘Grosfruchtiger,’ are used to produce fennel seeds grown for spice and medicine. A very successful self-seeder, herb fennel will become weedy if plants are allowed to shed seeds in the garden. 

How to Plant Fennel

Start bulb fennel seeds indoors in early spring, about 8 weeks before your last frost, and set them out under cloches when they have one true leaf. When growing fennel, prepare a fertile, well-drained bed in a spot that is convenient to water, because bulb fennel must have moist soil. Mix a standard application of a balanced organic fertilizer into the soil before setting out plants.

Fennel seeds also may be sown directly where they are to grow about three weeks before your last spring frost date. Space plants at least 12 inches apart. Start seeds for a fall planting of bulb fennel in midsummer, and set them out about 8 weeks before your first fall frost date. When growing fennel in fall, harvest bulbs before they are damaged by hard freezes.

Herb fennel is grown just like bulb fennel, but only one or two plants are needed by most households. Perennial fennel plants that are grown to produce fennel fronds and fennel seeds grow quite tall, to 5 feet, so they often are best located near the rear of the garden.

For recommended planting dates for your local climate — and to design your garden beds — try our Vegetable Garden Planner.

Growing Fennel

Keep bulb fennel seedlings carefully weeded, and drench plants with a liquid organic fertilizer when they are 12 inches tall. In early summer, mulch bulb fennel with grass clippings or another organic mulch to retain soil moisture, an essential factor in growing big, crisp bulbs. However, mulching too early can delay soil warming and invite problems with slugs. When growing fennel, do not allow the plants to run dry once bulb formation has begun.

Harvesting and Storage

Begin harvesting fennel bulbs as you can use them in the kitchen after the bulbs are more than 2 inches across. Bulb fennel plants grown in spring do not get extremely large, and should be harvested before the weather turns hot. If you cut the bulb high, so that the root and the base of the bulb remain in the soil, the stub will regrow a couple of small crowns with miniature fennel fronds — nice little tidbits to include in packets of frozen garden veggie mixtures.

With half of their tops trimmed off, fennel bulbs will keep in plastic bags in the refrigerator for a couple of weeks. Excess bulb fennel can be blanched and frozen. 

Propagating Fennel

All type of fennel produce yellow flowers followed by seeds in mid- to late-summer. To save seed from an open-pollinated finocchio variety such as ‘Perfection,’ allow two adjoining plants to flower and set seeds. When the flower heads dry to brown and seeds begin to fall, gather the seed heads in a paper bag, and allow them to dry indoors for a week. When thoroughly dry, shatter the seed heads and collect the largest seeds for replanting, and for use in the kitchen. Under good conditions, fennel seeds will store up to five years.

For growing advice for many more garden crops, check out our complete Crops at a Glance Guide.

Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on .