How to Grow Fennel

Days to germination: 7 to 14 days
Days to harvest: 80 to 90 days
Light requirements: Full sun
Water requirements: Regular watering
Soil: Loose and well-drained soil
Container: Not ideal for container gardening, but possible

Introduction

Fennel is a multi-purpose plant for your garden that will provide you with aromatic seeds for seasoning as well as a thick bulb for a vegetable. You can even eat the thicker stalks, like celery. The fine leaves can be snipped off and also used as an herb. The seeds have a licorice-like flavor very similar to anise, as do the other parts of the plant (those not as strongly as the seeds).

Fennel bulb is a popular ingredient in Mediterranean cuisine, and it can be eaten raw, grilled, or baked.

Though the plant can produce seeds as well as vegetable, you can’t get both from each individual plant. You have to harvest the bulb before the plant goes to seed. So if you want to use your fennel for all its uses, you’ll need to grow a few plants to take advantage of its versatility.

The plant is a perennial that can survive winters between growing zones 5 and 10. Some varieties of common fennel will not produce the fat bulb, so if you intend to harvest that as well you should plant Florence fennel.

The fennel bulb is high in vitamin C, and is also a good source of calcium, fiber and potassium.

Starting from Seed

Fennel doesn’t transplant well, so you can just sow your seeds straight out into the garden in the late spring after the frost threat has passed. Since your plants will come back each year, plan for a somewhat permanent location for your fennel.

Before you plant, dig the soil to loosen it up and add some compost for extra nutrients. For heavy or clay soils, add in some sand for extra drainage.

Seeds only need to be lightly covered by soil (perhaps and 1/8 of an inch), and should be kept frequently watered until they sprout their first few leaves. Space your seeds out around 10 inches apart. You might want to plant a few more than you need, and thin them down after they have sprouted.

If you are also growing dill in your garden, you must keep it as far from your fennel as possible if you plan on harvesting the fennel seeds. Fennel and dill will cross-pollinate and you will end up with very bland and odd-tasting seeds. Same applies for any coriander plants.

Growing Instructions

The bulb of the fennel plant grows at the base of the stalks, but not underground. Once the plant starts to develop the bulb, hill up the soil around it so that the sun doesn’t turn it green. This is called “blanching” and similar to the techniques used for growing celery. It keeps the bulb white and sweeter-tasting.

Once the bulbs are growing, water your fennel frequently so they don’t dry out. That’s if your intention is to harvest the bulb. If you are just after the seeds, then it is less important. Dry weather will encourage the plant to go to seed. This will ruin the bulb but is necessary for a seed harvest.

Give your fennel patch a fertilizer feeding each year in the spring with a standard fertilizer formula, or an addition of fresh compost.

Containers

As a perennial, fennel will become a fairly large plant with a very deep root system and is not ideal for containers. But with a large pot, you can keep potted fennel successfully. It should have a depth of at least 12 inches, but a 5 gallon pot would be a better option.

If you plant more than one plant in a pot that size, they will still grow and produce seeds but they will be too crowded to develop the vegetable bulb. This may work fine if you are only interested in the seeds anyway.

Fill it with light soil, with an extra layer of stone or gravel for added drainage. Fennel likes water, but not soggy roots.

Pests and Diseases

Fennel is not particularly at risk from many insect pests or diseases. You might sometimes find aphids or small whiteflies on the leaves, but they are seldom a serious problem. A spray or two of pyrethrin-based insecticidal soap will usually keep them under control.

The worst problem with fennel is root rot, which will damage your plants if you let them sit with wet roots for too long. Their soil should be light and well-drained, and you shouldn’t over-water the plants.

Harvest and Storage

You can start to harvest the leaves once your plants have become established and are growing well. Only take a few each time so you don’t harm the plant.

The bulb is harvested once it gets to the size of a small tennis ball. If you leave it to grow larger, the plant will likely bolt to seed and the taste of the bulb will almost immediately become bitter. Slice the plant off at the base of the bulb, right at the soil line. The bulb can survive a frost or two, so there needn’t be any rush to harvest your fennel when the cold weather arrives.

Harvesting fennel seeds is done in the fall when the flowers have turned brown, and they should be left to dry on the plant. Be careful when you go to collect the seeds as they come loose very easily. A bag or bowl under each flower is a good idea so none are lost.

Because fennels seeds very easily and the seeds will spread, you should try to collect all the seeds even if you don’t actually need them all. Otherwise, you will have fennel growing all over your yard come next spring.

Fennel bulbs should be stored in the fridge and used within a few days for the best flavor and texture. You can freeze it for longer storage, though it will lose a lot of taste when thawed out. Seeds can be kept in an air-tight container for 6 months or more as long as they are well dried.

25 Responses to “How to Grow Fennel”

sandy Says:
April 9th, 2011 at 7:15 am
If I plant a fennel “bulb” will it grow the small leaves?
fran Says:
January 2nd, 2012 at 1:04 pm
someone gave my bunnies a big bulb with stems and leaves, it sat out on our lanai for a couple weeks, one day it rained outside and the dead thing produced a volunteer that stood up and decided to live, then other little leaves followed..the lady who gave it to me, who is a gardener gave an audible gasp when I showed her, of course I protected it like a baby and a week or so later, planted my new friend and it looks pleased.
p-- Says:
April 20th, 2012 at 8:19 pm
half a fennel bulb in my fridge sprouted. i have put it in soil, but will it grow well that way?
Gina Says:
June 8th, 2012 at 7:11 am
How do I space the plants. They are bunched together now and I do not know how many inches or feet should be between each plant.

Thank you
Gina
johanna marquis Says:
August 5th, 2012 at 9:00 pm
question…. I have been unable to get my fennel to bulb despite planting the florence fennel. They form a tap root. Do female or male plants produce bulbs?
How does one tell the difference when thinning?
I plant seed in the spring, thin and to no avail but with the results of fine fennel leaves and a tall thin root. What’s the deal?
thanks.
this is my 3rd year of attempt and at a loss.
manny Says:
August 9th, 2012 at 7:52 am
Looking for the seeds only, how long does it take to harvest the seeds? And how many seeds can I expect from one plant?
Jay Says:
September 26th, 2012 at 8:24 am
This is the first time that I have grown fennel. I was pleased with the results, the plants did well and taste fine. I live in zone 4, can I keep the roots alive for next year by covering them with mulch and how thick a covering do they need?
Thanks,
Jay
LBW Says:
October 7th, 2012 at 1:29 pm
I have the same problem as Johanna Marquis. Lots of stock, long gangly roots and seeds, what is the problem
Rebecca Says:
November 12th, 2012 at 12:15 am
Adding sand to clay makes it even more like cement. Try digging in lots of compost and maybe some vermiculite to improve drainage. To get Florence fennel to form bulb try digging in bone meal (phosphorus = P in NPK). Your soil may be depleted. Don’t just add P as top dressing as it does not move well through soil. Get it down to the root area for best results.
Dean Says:
November 13th, 2012 at 8:50 pm
I planted Florence Fennel in my garden this year, but non of it formed bulbs. How do I make it form bulbs?
Karl Says:
March 16th, 2013 at 5:17 pm
Thank you for the information: should be quite helpful.
mary kay Says:
June 14th, 2013 at 2:26 pm
I planted a baby fennel plant in my garden in late April and it is now pretty big and has a heavy white root. I do not know when to pick the fennel to enjoy it’s licorice flavor. Last year the white root got so hard and had no taste. How do I know when this plant is ready to eat?
Christine Says:
July 15th, 2013 at 9:00 am
This is my first year of growing fennel – I bought the plant from a nursery and now its about 5ft tall flowers are starting to come and it looks at if there is just really good roots coming from the base but nothing else. What shall I do next? thank you
Kate Says:
September 4th, 2013 at 8:40 am
You stated that “Fennel is not particularly at risk from many insect pests or diseases. You might sometimes find aphids or small whiteflies on the leaves..”

What about Swallowtail caterpillars?! Fennel is one of the host plants for this beautiful butterfly’s larvae. The Black Swallowtail and the Anise Swallowtail use fennel as host plants, along with parsley, dill, rue, queen anne’s lace, and carrot. I grow fennel, rue, and parsley just so I can raise the butterflies 🙂 I hunt for their eggs and bring them in, still attached to the plant, into the house to raise.

If you’re growing Fennel to eat, then the larvae would definitely be a pest…they can strip a plant quickly! But try raising them…it’s a beautiful and astonishing process to witness.
INGE Says:
September 23rd, 2013 at 6:39 am
I planted Florence Fennel in my garden this year, but non of it formed bulbs. How do I make it form bulbs?
Emma Astill Says:
October 6th, 2013 at 11:46 pm
If I cut off a few stalks and leaves will the bulb fill out more? Some of my bulbs have plenty of stalks but a small bulb and woundered if this would help.
Mary Says:
October 29th, 2013 at 12:33 pm
My fennel is with lots of flowers,and if I leave it in the garden for winter will it survive.
anita Says:
December 19th, 2013 at 3:06 pm
can I grow fennel by planting the bulb?
David Moffitt Says:
January 19th, 2014 at 5:36 am
I’ve noticed that many people are asking the same questions over and over, so I decided I should address a few of them to help fellow gardeners. First, plants should be spaced 10 – 12 inches apart to allow for optimum bulb growth. As stated above: To get Florence fennel to form bulb try digging in bone meal (phosphorus = P in NPK). Your soil may be depleted. Don’t just add P as top dressing as it does not move well through soil. Get it down to the root area for best results.

Fennel is a perennial, so the roots should not be harvested. It is mainly grown for the bulb, and stalks for use in stews, etc. The seeds are great to add to baked goods and sauces to give them a slight licorice flavor. Leaving the seeds on the plant too long will over populate the area, so they should be removed once dry, but before they start falling off the plant. I personally place a baggie over the seed head, then snip it off of the plant, so the seeds stay contained in the bag.

Fennel also needs to not be planted near plants of the same types, eg: Dill and Coriander/Cilantro. They will cross pollinate, and ruin the flavors of each other.
Allexis Says:
May 20th, 2014 at 7:43 pm
I like that it says how you can grow it!!
Neil Says:
July 1st, 2014 at 4:50 am
We have just bought a house and the front garden is littered with fennel! I presume the whole root system needs to be completely removed?
eve Says:
June 26th, 2015 at 6:32 am
why are the bottom leaves of my fennel plants going yellow?
lyn bolton Says:
October 12th, 2015 at 3:52 pm
i have the same problem as a few others ,i have had fennel in for 4 yrs and never got a bulb otherwise plants thrive was told from nursery it was the bulb type .other viewers have commented that they have same with their florence fennel,please help me i love fennel
DMS Says:
October 19th, 2015 at 4:53 am
I planted fennel (as a starter plant) for the first time – intending to use for the bulbs. But I allowed the plant to seed. Do I need to remove and dispose of the bulb, leaving only the roots, to harvest bulbs next year?
JOSEPH FUSCALDO Says:
May 6th, 2016 at 6:41 pm
I ‘VE BEEN GROWING FENNEL FOR YEAR, LOVE IT, HOWEVER THE BUIBS OF MY PLANTS ARE QVAL SHAPED NOT ROUND, WHY?