Growing fennel is easy and it attracts pollinators to your greenhouse.
- Family: Apiaceae
- Botanical Name: Foeniculum vulgare
- Common Name: Fennel
- Type: Herb, Vegetable
- Light: Sun, Part Sun
- Zone: 4-9 (USDA)
- Soil pH: Neutral (6.5-7.5 pH)Size: 1’-6’ tall, 1’-2’ wide (up to 8’ tall in the wild)
Growing Fennel
Growing fennel is easy to do and it is a wonderful attractant for pollinators. Opinions vary on whether or not it is a good companion plant. Our recommendation is to avoid planting fennel near plants in the nightshade family.
Best Location in a Dome Greenhouse for Growing Fennel
Fennel is another plant that likes full sun. It can grow up to 6’ tall so choose a location where it will not block the sun from smaller plants.
Growing Fennel: Planting Seeds, Seedlings or Plants
Quarantine seedlings and plants before planting them in your greenhouse. This helps to avoid introducing pests.
Plant from seeds or transplant fennel seedlings. Large plants do not transplant well as the tap root is large.
Fennel Care
Fennel needs 6-8 hours of sun per day and will not do well if planted in the shade. Their preferred temperature is between 60-70ºF or 15-21ºC. It is best to grow fennel in zones 6-10. Fennel can overwinter, but will not survive prolonged freezing temperatures. That means you can grow fennel in your dome greenhouse!
Water your fennel plants on a regular schedule and do not let the soil dry out. Established fennel plants need an inch of water per week which will help the tap root to grow. Fennel is drought tolerant once established. However, soil that is too dry can cause your fennel to wilt and produce flowers.
The best way to water your fennel is to wet the soil rather than the leaves as wet leaves can burn. This can help prevent powdery mildew also.
Fennel Companion Plants
Companion plants are one of the tools we often suggest. They bring beauty to your garden, attract beneficial insects and can deter pests.
Fennel is an allelopathic plant and may not have many friends in the garden. Allelopathic plants secrete allelochemicals through their roots, leaves and seeds. With plants that are negative allelopathic the chemicals may suppress the growth of neighbors, especially plants in the nightshade family.
So how can you get around that? Plant fennel 4-5’ away from sensitive plants (beans, brassicas and tomatoes) and still have harmony in your garden. Or you can experiment and see what happens. Note: Many invasive plants are negative allelopathic plants.
Fennel and dill may cross-pollinate so we recommend planting them away from each other.
Growing Fennel: Managing Pests and Diseases
Fennel’s most common pests are snails, slugs and dreaded aphids. Snails and slugs can be pretty obvious as they can devour the whole plant and leave their glistening trail as a hint. (Sigh) Look for snails and slugs in your beds and around damp wood as they like to hide there during the day. You can put out beer traps for them to party in at night and remove them in the morning. (Snails can’t hold their liquor…) Other options are oatmeal traps or slug and snail pellets.
Note: Ants are attracted to the honeydew that aphids leave behind. Ant activity can be an indication that you have aphid colonies.
Powdery mildew may be an issue with fennel. Some helpful tips to prevent powdery mildew are: good sunlight, adequate spacing between plants, proper ventilation, careful watering practices and soil health. If you see powdery mildew starting in your dome greenhouse, remove affected leaves or plants immediately to prevent spreading the disease.
Growing Fennel: Harvest Time
Harvest established fennel fronds salads, pestos, sauces and more.
Some gardeners harvest fennel bulb as a “baby” or at about 3” in diameter. Fully grown fennel bulbs are typically 4-5” in diameter or about the size of a tennis ball. If you have a dog, maybe you can borrow his tennis ball for reference! If you enjoy pickling, try this recipe!
To harvest your fennel bulb, cut it at the base of the plant right above the tap root. To store fennel, cut the stalks and leaves an inch above the bulb. Harvest fennel seeds after the second year. Trim the flowering heads off and lay them out to dry. Once dry the heads will shatter and release the seeds. We recommend doing this inside your home or a controlled environment rather than your dome so you don’t end up with fennel sprouting everywhere in your greenhouse!
The History of Growing Fennel
The history of fennel includes culinary and medicinal uses along with the cultural uses. Fennel is native to southern Europe, especially along the Mediterranean Sea. The Romans have been eating fennel for more than 2000 years!
In Egypt fennel was both a food and medicine. Greeks and Romans used fennel as an insect repellant. In Europe there are three herbs used to make absinthe and sweet fennel is one of them. By the late 19th century it was a popular alcoholic drink in France and other European countries. Santé!
In Scandanavia fennel is one of the ingredients in brännvin, a distilled spirit. Fennel is rather spirited, don’t you think?
The first writing about fennel appears in Historia Plantarum (Inquiry into Plants) by Theophrastus (4th/3rd century BC). Fennel also appears in the writings of Hippocrates in the 5th/4th century BCE.
If you’re a fan of Greek mythology, there’s a story that Prometheus used a giant stalk of fennel to carry fire from Mount Olympus to Earth. Remember that wild fennel can grow to 8’ tall and sometimes has a 3” wide stalk!
Did you know the Greek name for fennel is marathon or marathos? That’s right, fennel is connected to the marathon! The Athenian Pheidippides carried a fennel stalk while running 150 miles to Sparta to gather soldiers for the battle of Marathon in 490 B.C. in a field of fennel. After the battle an Athenian messenger was sent from Marathon to Athens, which was about 25 miles, to announce the amazing defeat of the Persians.
Fennel Trivia
- Fennel means flattery in the language of flowers.
- Medicinally fennel has also been used to calm infants and relieve muscle spasms.
- Wild fennel can grow to 8 feet tall!
- Fennel seeds are an ingredient in bread, the flowers are edible and can be a garnish and the leaves can be added to salads or used as a garnish. The stems and bulbs are also edible. Some people grill the stems or you can add them to your salad for a bit of crunch.
- Fennel flowers are popular with butterflies, but if it’s an invasive plant where you live it’s best not to let it flower.
- Thomas Jefferson said this about fennel: “The fennel is beyond every other vegetable, delicious. It greatly resembles in appearance the largest size celery, perfectly white, and there is no vegetable equals it is flavour. It is eaten at dessert, crude, and with, or without dry salt, indeed I preferred it to every other vegetable, or to any fruit.”
Health Benefits of Fennel
Fennel has some wonderful health benefits and all parts of fennel are edible. The bulb is a wonderful source of vitamin C and both the bulb and seeds contain the mineral manganese. According to Healthline manganese is vital in enzyme activation, metabolism, bone development, wound healing and more.
Fennel seeds help curb the appetite and are used to aid in digestion. Another amazing benefit of fennel is that it has been shown to help relieve the pain of period cramps. Studies have shown that fennel reduces the production of oxytocin and prostaglandin, the hormones that make periods so painful for women. Now that makes it worth planting!
Happy gardening!
