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How To Grow Fennel

Foeniculum vulgare

Fennel | Foeniculum vulgare

A hardy, perennial European herb (Foeniculum vulgare) grown as an annual for its aromatic seeds and fragrant young leaves, both of which are used for flavoring.

In Florence or Sweet Fennel (var. dulce) the greatly enlarged leaf bases form a bulb-like structure 3 to 4 inches in diameter which is called the "apple". When blanched by earthing up it is cooked as a vegetable, but the stalks, resembling anise-flavored celery, can also be eaten raw.

Growing the Herb Fennel

As the seed is slow to sprout, sow it early in spring. The plants require full sunlight but only the simplest culture in any good garden soil.

As the plants grow rapidly, make successional sowings two weeks apart.

Fennel propagates well by seed, but can also be propagated by root and crown division. The seed can also be planted late in fall. When well established, thin plants to stand 8 to 12 inches apart in the row. Plants can also be started indoors and transplanted to the field when 3 or 4 inches tall.

Growing Cultures

Outdoors, in containers (sow directly in growing pots, do not transplant), and hydroponic cultures.

Plant Height

Fennel usually grows to a height of 18 to 24 inches (45 - 60cm).

Plant Spacing

Fennel plants should be spaced between 9 and 12 inches (22-30 cm) apart.

Preferred pH Range

Fennel will grow in a relatively wide pH range between 6.1 (mildly acidic) and 8.0 (mildly alkaline) with a preferred range between 7.0 and 8.0.


From seed. Direct sow outdoors in fall or in spring after last frost, Fennel does not transplant well.

Seed Germination Period

Fennel seeds will germinate in approximately 8 to 12 days.

Number of Seeds per Gram

There are between approximately 200 and 300 fennel seeds per gram, depending on variety.

Soil Requirements

Fennel will grow well in well-drained, deep and moderately fertile soils.

Alternative Growing Media

Soilless potting mixes (Pro-Mix, Sunshine Mix, etc.), perlite, vermiculite, coco peat.

Time From Seed to Saleable Plant

Seed to saleable plant in ten weeks.

Sun & Lighting Requirements

Fennel grown outdoors prefers full sun.

Fennel will grow indoors satisfactorily under high output T5 fluorescent plant lights or high intensity discharge (metal halide or high pressure sodium) plant growing lights. Keep high output fluorescents approximately one foot above the plants, and HID lights between 2 and 4 feet above the plants, depending on wattage. Have an oscillating fan gently stir seedlings for at least 2 hours per day to stimulate a shorter, sturdier, and more natural plant habit.

USDA Hardiness

8a to 10b. Fennel florance grown as annual.

Water Requirements

Water regularly, being careful not to overwater. Allow soil to go almost dry between watering, then soak thoroughly.

Potential Plant Pests and Diseases

Fennel can be susceptible to aphids and damping off.

Companion Planting

Fennel is only beneficial to dill, and in fact is detrimental to almost every other plant species. Dill is one of a very few known plants that will successfully grow near fennel. Fennel attracts ladybugs, syrphid fly, and tachinid fly and repels aphids.

Special Notes

Fennel is known to attract bees, butterflies and birds. Suitable for containers. Fennel should not be planted near almost all plants, as it can inhibit growth, cause bolting, or actually kill other plants.

Buy Fennel Seeds by Botanical Interests

Heirloom Fennel Florence Finocchio Seeds
Sweet licorice flavored "bulbs" (90 days), and delicately flavored, feathery foliage.

Organic Fennel Florence Perfection Seeds
Larger, more uniform "bulbs" & delicately flavored foliage. Developed for cool, northern climates.