How to grow fennel at home – best way for early harvest

Fennel can be started from seed indoors in pots or planted directly outdoors when there is no longer any risk of frost. Fennel prefers a slightly acidic (pH 5,5-6,5), fertile, and well-draining soil. 

You will find that fennel is easier to start from seed. To propagate from root cuttings or plant division is more difficult as the fennel plant, like dill and cilantro (coriander), develops a long and delicate taproot that does not respond well to handling.

We grow fennel at home, and it is one of our favorites. As an aromatic herb, fennel offers an easy-to-recognize anise-like flavor and scent. And much like, for example, horseradish and cilantro (coriander), its robust flavor profile ensure that a little goes a long way.

For us, fennel is both a garden vegetable and an aromatic herb. We use the fine leaves and root bulb as a vegetable while the dried seeds are a loved herb to be used in both cooking, teas and baking.

Quick Facts:

Name: Fennel (Foeniculum Vulgare)
Height: 1,5-2,1 meters (4-7 feet)
Soil: Prefers well-draining, fertile, and slightly acidic soil 
Description: Hardy to a half-hardy perennial aromatic herb that is often grown as an annual. Easily confused with dill. The fennel plant is bright green with feathery leaves and clusters of tiny flowers. 
Use: Harvest and use leaves, bulbs as well as seeds for cooking, baking, and spice mixes.

The bright green and delicate fennel leaves are great in salads and cold sauces
Fennel plant with the characteristic feathery leaves

How to start fennel from seed – a proven method

Our proven method for growing fennel starts indoors about 4-6 weeks before the last expected frost.

Young fennel seedlings and plants do not tolerate frost and freezing temperatures. Starting indoors ensures an early start, protects from surprise weather, and gives us an earlier harvest.

1. Choose your starter pot

Use a seed starter tray with a covering plastic dome or regular starter pots that you cover with plastic. 

And as always, all pots need drainage holes.

2. Use a slightly acidic soil

Fennel prefers a slightly acidic potting soil mix. It is essential to choose a potting soil mix that drains well. 

3. Start seeds in groups of 3 – 5 seeds per pot

Plant your seeds in groups of 3-5 and approximately 1 cm (½ inch) deep. Take care to place the seeds close to each other, not on each other.

I usually sprinkle the fennel seeds across the top and then cover them with soil. Later I will snip or cut unwanted seedlings keeping only the two strongest in every pot.

You can plant 1 seed per pot if you know your seeds have a 100% germination rate. But from experience, I know that a 70% germination rate is reasonable to normal why I always plant fennel seeds in groups. 

Starting several fennel seeds per starter pot (17 May)
I usually start 5 or more fennel seeds per pot.

Also, there is no guarantee that all germinating seeds will produce vigorous seedlings. So, play it safe and plant a few more seeds than the number of plants you plan to grow.

Keep the growing environment moist to help your seeds germinate by covering them with plastic. We use seed starter trays with plastic domes. But you can use a starter pot and cover it with plastic film.

You can also pre germinate your fennel seeds using the paper towel method. This way you make sure you are only using strong and viable seeds. 

4. Remove cover as seeds sprout first leaves

Expect the first leaves or cotyledons to sprout in about 7-10 days.

Remove the dome or covering plastic film as the seeds germinate and sprout first leaves. Place the seedlings in a location with good light for at least 6 hours per day. 

Fennel seeds sprouting first leaves or cotyledons after about 1 week (23 May)
First leaves sprout after 1 week. Place in a location with good light and remove the cover.

The seedlings need good light to avoid growing leggy. Still, you do not want to place the seedlings in a location that gets too hot. Think light, bright, and room temperature. 

5. Select the most robust seedlings

When starting 3-5 seeds per pot or cell, you are bound to have more than 1 seedling per space. At least in some pots or cells.

As the fennel seedling develops a delicate taproot, we do not try to prick out (video tutorial) or divide the seedlings (video tutorial). Instead, snip or cut the weaker seedlings (video tutorial), leaving only the two most vigorous and dominant seedlings.

Do not try to remove the weaker seedlings by the root as you risk disturbing the root system of your chosen dominant seedling. Cutting the weaker seedlings will ensure that they wither down and die. Read more about How to thin seedlings without killing them.

6. Transplanting fennel seedlings outdoors

Transplant your two dominant seedlings when they are large enough to handle, and there is no longer any risk of frost.

Do not attempt to separate the two seedlings growing in the pot. Treat them as one seedling and transplant the whole pot.

You can of course snip all but one seedling and only keep the most dominant. But since I harvest my fennel bulbs early I have found it ideal to grow fennel in pairs. I find larger fennel bulbs less tasty and prefer to grow more smaller bubs. 

Whereas fennel does not mind cool weather, young plants will not tolerate frost. This is also the reason we start fennel in pots indoors. We like to get a head start but do not want to risk being caught by a late onset of frost or snow. 

Plant seedlings 30 cm / 12 inches apart and allow 40 cm / 16 inches between rows. 

7. Mulch, “earth up” the bulbs, and water a lot

Mulch your garden bed with straw to help with soil moisture while protecting against soil-borne diseases and pathogens.

Feed your garden bed with compost or other organic matter to keep the soil productive. Fennel prefers fertile soil that drains well, and you should be prepared to water daily.

As the fennel bulb grows, add more soil around the bulb to help it grow larger and more robust. But do not get dirt between the forming leaves when you “earth up” your fennel bulbs.

How to harvest fennel

Fennel plants let you harvest fresh fennel greens, bulbs, and seeds.

You can pick fresh fennel greens continuously as the plant grows and develops. To help the plant grow back, do not harvest more than ⅓ of the fennel greens at any time. 

Fennel bulbs take anything from 14-18 weeks to grow and develop. Harvest the bulbs when they measure approximately 7 cm / 3 inches across. If you let the bulbs get too big, they get fibrous and very chewy. 

Harvest fennel seeds from the clusters of tiny flowers that are dried. Cut the stems and hang them upside down inside a brown paper bag. As the flowers dry, shake the branches highly, and the seeds will fall off.

How to store your fennel harvest

Fennel seeds are best stored or preserved dried. Keep them in airtight containers in a dark, warm, but not hot place. 

Fennel greens can be dried or stored in the freezer in airtight bags. 

You can store fennel bulbs in portion-sized pieces in the freezer. Cut or cube the bulb and blanch for 30 seconds in salted water. Next, place in ice-cold water until cool. Drain and dry the fennel pieces before freezing in containers or freezer bags. 

How to propagate fennel

Fennel is best propagated from seeds. As the fennel plant develops a central tap root, it is challenging to propagate fennel by root cuttings or plant division.

Companion plants for fennel

I am yet to read about a good companion plant for fennel. Still, from my experience, fennel is excellent at attracting pollinators, and I have not found it to hurt my other plants.

It is, however, commonly accepted that aromatic herbs can help keep harmful pests and even deer away. [1]

So, I will continue to grow aromatic herbs like fennel, basil, rosemary, sage, lavender, and peppermints in my garden. And so far, it works well.

I do not grow dill next to fennel as they are closely related and a trusted gardener told me they will cross-pollinate. 

Known pests and diseases

Most of the herbs and vegetables I grow have been attacked by aphids, snails, or fungus gnats at some point. I use Neem oil to keep these and many other pests and diseases at bay.

But fennel is also susceptible to fungal diseases like leaf blight, Downy mildew, and Powdery mildew. Aside from aphids, pests such as armyworms, cutworms, and root-knot nematodes can also attack fennel plants. [2]

How to use fennel

Fennel is a versatile aromatic herb with a pleasant anise-like flavor and scent. And it is an exciting plant where the fruit and the seed are the same. 

Fennel seeds are great for dry rubs, spice mixes, veal, pork, and fatty fish like mackerel, salmon, and tuna. 

Use the delicate leaves for fresh and flavorful salad greens or to flavor dips and dressings. 

Another favorite is to use the fennel bulb and thicker stems. Choose to cut into pieces and roast or barbecue for a real treat. Or slice thinly and serve in a salad or place on top of, for example, fish in a tin foil bag placed on the barbecue. 

Helpful resources:

[1] https://extension.oregonstate.edu/news/herbs-rescue-fend-deer-aromatic-plants

[2] https://plantvillage.psu.edu/topics/fennel/infos

Meet the author: Mattias is an experienced gardener spending most of his free time on his knees among herbs, plants, and garden vegetables. For the past two years, he has been sharing gardening projects and how-to tutorials on the NordicLavender website and YouTube channel.