Bulb Fennel: Learn About When And How To Harvest Fennel Bulbs

How and when do I harvest my bulb fennel? These are common questions and learning how to harvest fennel bulbs isn’t difficult at all. When to harvest fennel bulbs involves a little more, but before we talk about the how and the when, let’s make sure we’re talking about the right fennel.

Fennel is an herb that grows freely in gardens throughout the USDA hardiness zones 5-10. The seeds and leaves can be used in a variety of recipes, including flavoring for Italian sausage, and the leaf stalks make a different and wonderful vegetable dish.

There are several species available for this use, including Foeniculum vulgare (common fennel), the wild fennel that grows along the roadsides in many parts of the United States. However, if you want to talk about harvesting fennel bulbs for your table, you must plant Florence fennel, a variety of Foeniculum vulgare called Azoricum. In Italy, where this variety has been cultivated for centuries, it is called finocchio. This is the only variety to plant if your goal is harvesting fennel bulbs.

When to Harvest Fennel Bulbs

When do I harvest my bulb fennel? Fennel bulbs take about 12 to 14 weeks from seed to harvest and depend on cool weather for bulb development. If the weather becomes unseasonably warm, all fennel, including finocchio, will bolt, which means it will produce flowers too soon and the bulb won’t form. When conditions are right, when to harvest fennel bulbs depends solely on their size.

As the bulb grows, measure it with a ruler. The bulb should measure at least 5 cm (2 in.) in length but no more than 7 cm (3 inches), about the size of a tennis ball. Harvesting fennel bulbs larger than this will be disappointing as the bulbs tend to get stringy and tough with age.

Now that you know when to harvest fennel, let’s talk about how to harvest fennel bulbs.

How to Harvest Fennel Bulbs

Use a pair of garden shears or a sharp knife to cut off the plant’s stalks and leaves, leaving an inch or two at the top of the bulb. Don’t discard the greenery! Use it for another dinner as a salad addition or side dish.

Carefully clear the soil away from the base of the bulb. If your soil is loose, you can use your hands. If not, use a small garden trowel but try not to nick the bulb. Now, hold the bulb and use a sharp knife to slice the bulb away from the roots. Ta-da! You’ve just learned how to harvest fennel bulbs!

Clean your fennel bulbs with water, and if possible, use them right away while the flavor is most potent. If you can’t use the bulbs immediately, store them in an airtight plastic bag in the refrigerator for up to a week. Remember, your bulb will begin to lose flavor as soon as it is cut so use it as quickly as possible.

So, when do I harvest my bulb fennel? Right when I need it! I plant my seeds a few at a time so bulbs don’t all form at once. I slice them in salads and stir-fry, roast or braise them and enhance their flavor with mild Italian cheese. They’re a different and enjoyable dinnertime treat that can only be experienced during a limited time of year, and that makes them something special.

Harvesting fennel bulbs straight from your garden can be a treat for you, too.

Fennel, from seed to harvest

Fennel is a plant for which the roots are the part we eat and its nutritious and culinary value is exceptional. It is a very good summer vegetable.

Foremost fennel facts

NameFoeniculum dulce
FamilyApiaceae (parsley family)
Type – biennial

Height – 16 to 24 inches (40 to 60 cm)
Exposure – full sun
Soil – ordinary to rich

Harvest – July to December, 3 months after sowing

Types of Fennel

The kitchen gardener can choose from sweet fennel, Florence fennel and bronze fennel (Foeniculum vulgare ’Purpureum’, hardy in USDA zones 4 through 9), among other varieties, to grow in the veggie patch or herb garden. Sweet fennel is also called common fennel, and bronze fennel is sometimes referred to as copper fennel. After just one taste of a fennel seed or leaf or a slice of a Florence fennel bulb, you can easily tell these plants are closely related. The characteristic anise flavor is common to all three plants.

Sweet, bronze and Florence fennel look similar, too. They produce flat heads with many tiny yellow flowers in mid- to late-summer, and their leaves are finely dissected, giving them a decorative, feathery appearance. Sweet and Florence fennel leaves are yellow-green, and bronze fennel’s leaves are purple-bronze. Fennel flowers are attractive to butterflies, and fennel is a host plant for the caterpillars of black swallowtail and anise swallowtail butterflies.

Sweet fennel is a tall plant, and it doesn’t form Florence fennel’s characteristic bulblike structure at the base of it stems. Sweet fennel grows to 4 to 6 feet tall and 1 1/2 to 3 feet wide, whereas, Florence fennel grows to 2 to 3 feet tall and 2 to 3 feet wide. Bronze fennel sits in between, growing 3 to 5 feet tall and 2 to 3 feet wide, and it also doesn’t form Florence fennel’s bulb.

Top Fennel Varieties

The biggest choice you have is deciding whether you want to grow herb fennel or Florence fennel. After you’ve decided that, there are some good varieties to choose from in either category.

Herb Fennel Cultivars:

  • ‘Grosfruchtiger’– Probably the best and most frequently grown green fennel variety. Plants are very vigorous, and the leaves have great flavor.
  • ‘Dulce’– Another green-leaved cultivar grown for the foliage and seeds.
  • ‘Rubrum’– A popular variety of bronze fennel. Leaves and seeds of this cultivar are edible, but it can also be grown for ornamental value.
  • ‘Purpureum’– Another ornamental or herb garden cultivar with bronze-purple leaves.

Florence Fennel Cultivars:

  • ‘Fino’– This variety is slow to bolt, reliable, and has a strong anise flavor. Bulbs are a good size and best planted late summer for a fall harvest.
  • ‘Orazio’– This cultivar develops very large and thick round bulbs. Higher yield than other varieties.

Different varieties of fennel will have either rounded or flat-ish bulbs. They typically take 70-80 days to mature, making them a better crop to grow in the fall than in the spring.

  • ‘Orion’– This variety has compact plants that still produce good size bulbs. Good for spring or fall harvest.
  • ‘Solaris’– Fast-growing and matures before many other varieties. Bulbs are large but semi-flat instead of round.
  • ‘Mantovano’– A great-tasting variety that matures quickly and can be harvested as either baby or full-size bulbs.

How to Grow Fennel

This article was co-authored by Andrew Carberry, MPH. Andrew Carberry has been working in food systems since 2008. He has a Masters in Public Health Nutrition and Public Health Planning and Administration from the University of Tennessee-Knoxville.

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Growing fennel is a wonderful way to add spice to recipes using home grown ingredients. The pungent aroma is considered inviting, while the rich, earthy flavor is known to significantly contribute to the taste of many dishes. Fennel is high in vitamin C and has been used as an herbal remedy for digestive issues for many thousands of years. In addition, its delicate, green fronds are aesthetically pleasing, making fennel an excellent addition to any garden. Start with Step 1 below to learn how to grow fennel.

Fennel Care

The fronds, bulbs, and seeds of fennel are all edible. Source: willsong

The key to growing bulb fennel is sowing seeds at the right time and avoiding heat waves! Follow the care tips below on how to grow fennel in your own garden.

Sun and Temperature

Both types of fennel require a minimum of 6-8 hrs of direct sunlight per day. They will not tolerate shade so be careful not to overshadow with another crop in your garden. They grow best in USDA zones 6-10 with ideal temperatures ranging from 60-70ºF (15-21ºC). As a perennial, common fennel will overwinter outside, but may not survive prolonged freezing temperatures. Summer sown bulb fennel can be harvested right up until the first frosts. In milder climates, it can be overwintered and treated as a biennial for seed production. Plants benefit from mulches to retain moisture in summer and heat in winter.

Water and Humidity

Fennel requires consistent and regular watering throughout the growing season. Dry soils will cause common fennel to wilt and reduce seed production. It will also trigger bulb fennel to flower. Timed soaker hoses early in the morning or drip systems are perfect for providing consistent irrigation. Avoid wetting the foliage during high summer to prevent sun scorch. Overwintered common fennel does not require regular watering, but do not let the soil dry out.

Grow fennel in fertile, well-drained, moisture-retentive sandy loam soils, improved with lots of well-rotted organic matter. Do not allow the soil to dry out. Suitable to grow in pH 6–8.


Apply lots of well-rotted organic matter such as farm-yard manure or compost to the planting site at least six weeks before planting. A balanced slow-release fertilizer can be added to the seedbed prior to planting as an extra boost. When bulbs begin to swell apply a nitrogen-rich liquid fertilizer once every two weeks until harvest. Mulch herb fennel in springtime for added nutrition.


Stems of common fennel can be pruned back to ground level after seeds are harvested. Fennel plants that are grown for ornamental use often retain the dried seed heads to provide winter structure in the garden. This can result in self-seeded plants popping up around the garden in spring, but these are easily weeded out. Prune any developing bulb fennel flower spikes to stop them from bolting.


Common fennel: For best results, common fennel seeds should be sown directly into pre-watered drills ½inch (1½cm) deep and rows 12 inches apart (30cm) after the last frost date and when soil temperatures are a minimum of 50ºF (10ºC). When seedlings are 2-3inches (5-8cm) high, thin to 18inches (45cm) between plants.

Mature common fennel plants may be propagated by division with varied success due to problems with disturbing its taproot. Plants may be dug up in spring when shoots begin to appear. When removing the plant ensure the entire root system remains intact. Viable side shoots can be removed from the main crown and potted into a sandy compost mix and grown in pots until new roots have established. Once roots have filled the pot, plant into a new growing position.

Bulb fennel: Start sowing seeds indoors from mid-spring. Sow into small pots or module trays filled with compost, ½inch (1½cm) deep. Germination usually takes 1-2 weeks. Sow two seeds per pot/module cell and nip out the weaker seedling when they are around 2-3 inches high (5-8cms) and ready to plant out. Acclimatize young plants to outside conditions for about a week before planting into final growing positions. Space plants as above for common fennel. Florence fennel seeds may be sown directly in the same way as common fennel.

How To Use Fennel

Thomas Jefferson was positively crazy about this vegetable, declaring “it is beyond every other vegetable, delicious … indeed, I preferred it to every other vegetable, or to any fruit.” Somehow, his fervor never spread, resulting in fennel’s continuing, relative obscurity in the New World. Don’t let unfamiliarity discourage you, however. If you have the space for the fronds of friendless fennel, you may find that it is both fun to eat and experiment within recipes.

The flavor profile is intensely aromatic and reminiscent of licorice and anise, but with a sweetness. To me it is a distinctly Italian experience, pairing well with citrus, fish, or spiced meat like sausage, but if you didn’t grow up with it, the flavor may have a bit of a learning curve. It is most strongly flavored when raw, so if you find it too much, just cook it to mellow.

As the plant begins its feathery spread, you can pluck the dill-like branches and either chew them raw for instant fresh breath or steep them in a comforting tea that is excellent both hot and cold. One of my favorite summertime brews is sun tea with a handful of fennel leaves, lemon balm, and mint — naturally sweet, and so refreshing!

Get ready for a generous load of flowers! Wren Everett / Insteading

When you harvest the tasty bulb of Florence fennel, cut it so a bit of the base and the roots are left in the ground. The second flush of stems and leaves will extend the flavorful harvest. Sweet fennel stalks, with their hollow centers, make for innovative and flavorful “straws” for use in summery drinks.

The bulb is delicious raw in salads or caramelized in the oven. The celery-like stalks can be candied while tender before the plant bolts in summer’s heat. Even if you find the stalks too tough later in the season, they can still be simmered in a flavorful stock with other vegetables, or cooked alongside fish.

When the dill-like flowers emerge, enjoy the visiting butterflies, and collect fennel pollen if you so desire. A sprinkle of this currently trendy ingredient on a finished dish may make your kitchen feel like it deserves a Michelin star, but no one will have to pay the associated price tag.

When the seeds form at the end of the umbel, collect some for next year’s planting and then use the rest as sausage spice, a warming ingredient to masala chai, a stand-alone tea to soothe an over-indulged stomach, or chewed straight for a naturally fresh mouth. The fennel plant will readily self-sow (some say TOO readily) so be proactive in catching those seed heads if you don’t want a permanent fennel patch.

Do any of you grow your own fennel plant and share Thomas Jefferson’s love of it? What’s your favorite way to use it? Let me know in the comments below!

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