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Fennel: Planting, Growing, and Harvesting Fennel Bulbs | Almanac.com

How to Grow Fennel: The Complete Guide

Fennel Bulb
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Nnattalli
Botanical Name
Foeniculum vulgare var. azoricum
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Planting, Growing, and Harvesting Fennel

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Delicious, vibrant colored, and easy to grow, fennel is a beautiful addition to your garden and kitchen. Learn how to plant, grow, and care for beautiful fennel.

About Fennel

Fennel is grown as a tasty vegetable, as an ornamental for its beautiful and delicate foliage, as a pollinator attractor, and for its pungent and flavorful seeds. Easy to grow by direct seeding in midsummer, fennel deserves a spot in your herb garden or flower bed.

Florence fennel is the common name for Foeniculum vulgare var. azoricum, the biennial bulbing fennel grown as an annual for eating. While it can grow quite tall, shorter varieties are available, perfect for smaller spaces. 

Also called finocchio, this tasty vegetable is used for eating fresh, baked, and roasted, as an ingredient in soups, and its fresh leaves are used to flavor teas. The seeds are likely familiar to you as an essential flavoring in Italian sausage, as well as pastries and candies. It’s also one of the ingredients in the famous Chinese five-spice powder.

While not a native, fennel is a lovely and functional plant for pollinators, and the plant is a host for anise swallowtail and black swallowtail caterpillars! It can spread in warmer climates but rarely does so in cold areas.

Planting

Florence fennel likes full sun and fertile, well-drained soil. Work some organic matter in, but don’t overdo it. Soil that is too rich will result in bland, flavorless bulbs and foliage. A neutral pH of 6.5-7.5 is ideal for these heavy feeders.  

Common fennel can grow as high as six feet tall. If growing as an ornamental, place it in the back of a bed where its delicate foliage can be seen but won’t block the view of other, shorter plants.

When To Plant Fennel

Fennel can be planted in spring, as soon as the frost danger has passed, but is better grown as a fall crop. It is prone to bolting if it matures during hot weather and long days. Instead, plant fennel in midsummer for a fall crop. 

Since fennel does best as a cool-weather crop, it’s perfect to plant in your garden when earlier maturing crops are finished. Time it to be ready just before your first frost, as the foliage and bulb are only lightly frost tolerant. Direct seed about 80 days before your first frost date, depending on the variety.

How To Plant Fennel

Fennel can be directly seeded or transplanted, although transplanting can be tricky due to the tap root. Soaking fennel seeds for 24 hours can aid in germination.

To start fennel indoors:

  • About 4-6 weeks before your last frost, sow 2-3 seeds per cell in standard trays or soil blocks. 
     
  • Sow seeds ¼ inch deep. 
     
  • After germination, thin to one seedling per cell by snipping, not pulling.
     
  • Harden off seedlings before transplanting into the garden.
     
  • Fennel can be transplanted outdoors as soon as frost danger has passed. Don’t start them too early–fennel forms a taproot and can suffer extreme transplant shock if the taproot is injured.

Direct seeding after the last frost in spring or in midsummer:

  • Prepare the bed with compost, working it into the soil. 
     
  • Sow seeds ¼ inch deep, about one inch apart, in rows 18 inches apart.
     
  • Gently water the seeded area. 
     
  • Once plants have a set of true leaves, thin to a spacing of 6-9 inches apart. 
Growing
  • Fennel likes fertile soil high in organic matter.
     
  • Mulch to keep soil moisture even and slightly moist. 
     
  • Fennel typically blooms in the second year but can bolt in the first year (ruining the crop) if exposed to high heat and long days. If your transition from spring to summer is early and rapid, consider a late summer into fall crop for better success.
     
  • Fennel likes an inch of water per week or more but is drought tolerant once established (thanks to that taproot). 

Tip: Water in the morning. The plants will have water available during the heat of the day when needed most, and foliage will have a chance to dry before nightfall. Constantly damp vegetation can cause fungal issues. If your mornings are busy, consider a timer to turn your irrigation on and off.  

Harvesting

Fennel is grown as an annual for foliage and as a vegetable. Its tasty bulb can be harvested early as “baby” fennel, at about 3 inches in diameter, or allowed to mature to a 4-5 inch size fully. Many people prefer to harvest their fennel when the bulb is the size of a tennis ball for the best flavor and texture. 

  • Harvest using a garden knife or pruning shears, cutting at the base of the plant above the tap root. 
     
  • Store fennel in a cold environment with high humidity. If storing, cut the stalks and vegetation off about an inch above the bulb.
     
  • Fennel seeds from second-year plants can be harvested when the flower head has turned brown. Snip off the heads and lay them on a screen or tray to dry. The heads will shatter, releasing the seeds. 
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Wit and Wisdom
  • Fennel has been enjoyed as a culinary treat and has been used for medicinal purposes since ancient Greek and Roman times. 
     
  • Fennel can cross-pollinate with dill, causing unwanted flavors in both, so plant far away from each other. 
Pests/Diseases
  • Root rot in wet soils.
About The Author

Andy Wilcox

Andy Wilcox is a flower farmer and master gardener with a passion for soil health, small producers, forestry, and horticulture. Read More from Andy Wilcox

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