Fennel

While fennel can be a finicky herb, the pay-off is its subtle licorice flavor.

VarietiEs

Herb or leaf fennel, and bulb fennel.

WHERE FENNEL THRIVES

Regional compatibility

This herb is a tender perennial, considered an annual in cold regions, so it cannot be grown year-round in all climates. Fennel will grow as a perennial when minimum temperatures range from 0 to 40 degrees.

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Optimal shade & sun

Full sunlight—fennel appreciates at least six hours per day.

RESILIENCE

ADAPTABILTY TO CLIMATE EXTREMES. Fennel does not adapt well to dramatic changes in temperature. It prefers cool weather but is quite sensitive to frost and dies out in extreme cold. In hot weather fennel is susceptible to bolting.

DROUGHT RESISTANCE. Native to the Middle East and Mediterranean, lavender is certainly drought resistant. In fact, it’s one of the plants most used in drought-tolerant landscaping. However, it does require regular watering while it is first getting established in the garden.

PREP YOUR SOIL

OPTIMAL SOIL TYPE. Fennel grows best in a well-drained, moist, and fertile soil.

PLANTING

After the final spring frost, plant fennel from seed. Push the seeds no more than a half-inch deep and 6 to 12 inches apart. You can plant fennel indoors 4-6 weeks before your last frost to get a head start on spring planting. Place 2 seeds per pot and thin to 1 seed once plants reach 2 inches tall. Avoid disturbing the roots when transplanting into the garden to prevent your fennel from bolting.

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Best time of year to plant

Fennel is sensitive to cold weather, so plant after the last spring frost.

Companion plants

Fennel is allelopathic, capable of producing chemicals that inhibit other plants from germinating. Allelopathic plants can release chemicals from their roots, leaf tissue or in the case of fennel, the seeds themselves are toxic to most annual plants. Beans, tomatoes, and eggplant are particularly sensitive to fennels allelopathic effects. Don’t let fennel’s aversion to neighbors prevent you from planting it in the garden. Fennel’s aroma and flowers are a beneficial insect magnet and great for attracting pollinators to the rest of the garden. Consider planting fennel in an isolated corner of your garden.

Growing

Fennel will be ready for harvest within about 2 months. Mature fennel can grow to 5 feet or more so it is best planted in the back of the garden where it wont shade other sun loving plants.

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WaterinG

Fennel prefers a moist environment, so water consistently if you want bitterless bulbs. If the top inch of soil is dry, give it a water. If it is the seeds you are after, reduce the amount of water by half when fennel starts to bloom as too much water will prevent seed production.

Mulching

Mulch this herb once it is established (over 5 inches tall) to promote moisture retention and weed suppression amongst your plants. Place any material from wood chip to straw on the soil surface up to 2 inches thick.

Fertilizing

Mix compost, made from yard clippings and food scapes, into the soil before planting to increase soil fertility. Once fennel begins to bulb, feed your plants once with a high in nitrogen fertilizer (21-0-0), about 3 tablespoons for every 12 feet of garden soil, to ensure robust bulb development.

Weeding

Keep your fennel clear of weeds, which will compete for and suck up nutrients and sunlight.

CHALLENGES

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PESTS. Parsleyworm eats fennel so pick it off when you see it. If you can’t catch them all, don’t worry. The lowly parsleyworm eventually turns into a black swallowtail butterfly, which pollinates gardens.

DISEASES. Leaf blight, mildew and root rot plague fennel in waterlogged soils—keep your soil well-drained amidst the moisture by adding organic matter to your soil before planting and reducing soil compaction caused by heavy foot traffic. You can also reduce the risk of mildew in humid and damp climates by spacing your fennel farther apart to increase air circulation around your plants.

OTHER CHALLENGES. Fennel is a bit touchy and has a limited temperature range, so if it gets too cold, you may need to cover it. Fennel grows best when daytime temperatures are between 60 and 70 degrees. Consider using a floating row cover to protect your plants from chilly nights that drop below freezing. Floating row covers are lightweight fabrics that you place over your plants. Depending on the thickness, row covers can increase the ambient temperature around your plants by a few degrees preventing any damage caused by frost. Row covers also have the added benefit of keeping pests off of your plants!

HARVEST

Fennel can typically be harvested 2 months after planting, and are prime for harvest just before they flower. If you are harvesting leaf fennel, clip sprigs or cut the whole stalk and enjoy. Leave a few stalks to let go to seed so you can enjoy the licorice tasting flowers and seeds! If you are harvesting bulb fennel, wait until the bulb reaches the size of a tennis bulb. Use a harvesting knife and slip it gently below the bulb and cut the tap root away from the bulb. Smaller bulbs are more tender compared to larger bulbs which quickly become tough and bitter.