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Bulb fennel is a delicious vegetable with crisp licorice-flavored bulbs and leaves. Considering its many uses in the kitchen alone, growing bulb fennel from seeds or transplants is well worth the effort. Nearly every inch of this nutritious and versatile vegetable is edible, from its bulb and leaves to its pollen and seeds. Plus, it’s not difficult to grow and thrives in garden beds as well as containers. If you’re interested in planting bulb fennel, this article will help you grow large and flavorful fennel bulbs with ease.
What is bulb fennel?
Also known as Florence fennel (Foeniculum vulgare var Azoricum), bulb fennel is a versatile, cool-weather vegetable that produces large, celery-like stalks and fleshy bulbs which make delicious additions to salads, stir fries, soups, stew, and more. Florence fennel leaves, seeds, and even Florence fennel pollen are also edible and very nutritious. While bulb fennel is a good source of fiber, potassium, and vitamin C, Florence fennel seed is calcium- and magnesium-rich.
Grown as annuals, fennel bulbs aren’t the same as herb fennel, which is grown as a perennial. (See the next section for details on herb fennel.) Bulb fennel plants thrive when grown in their own designated plot or even in containers. As long as you have a well-draining, sunny location, you should be able to succeed with homegrown bulb fennel. What’s more, you can also use the fragrant greenery of bulb fennel to add texture to cut-flower bouquets.
Bulb fennel vs leaf fennel
Both bulb fennel and leaf or common fennel (Foeniculum vulgare) hail from the Mediterranean and taste and smell a bit like anise. However, bulb fennel plants are shorter in stature than their common fennel relatives which can grow up to five or six feet high. Bulb fennel is also shorter lived. Common or “sweet fennel,” by contrast, is a perennial herb, meaning its delicate, feathery foliage will spring back up year after year.
Like bulb fennel, leaf fennel has plenty of use in the kitchen. Its edible stems, leaves, and seeds have a strong anise-like flavor, and fennel herbs and seeds have long been used to flavor classic Italian sausage. Just keep in mind that, although it may be tempting to use the terms “fennel seed” and “aniseed” interchangeably, they aren’t actually the same. Aniseed comes from yet another herb—anise (Pimpinella anisum.)
Many gardeners also use leaf fennel to attract and support various beneficial insects. Bronze fennel, in particular, is an important larval host plant for multiple types of swallowtail butterflies.
The best site for growing bulb fennel
The most suitable sites for growing bulb fennel are those which afford full sun and well-drained soil. The soil itself should be rich in organic matter. If yours needs a boost, amend with compost or worm castings ahead of planting.
Pro tip: Fennel naturally releases allelopathic chemicals which can affect the growth of neighboring plants. As a result, give potentially sensitive crops like tomatoes, potatoes, beans, and eggplants plenty of distance from your fennel. (If need be, you can grow fennel in a large container or in a few separate pots.)
When to plant bulb fennel
Ideally, you should plant bulb fennel when the soil temperatures in your area are consistently between 50 and 75 degrees F (10 to 24 degrees C.) That means, if you want to direct sow seeds or transplant seedlings, you should do so as soon as the last frost danger has past. I also like to grow bulb fennel for autumn harvesting with the plants doing very well in the cooler shorter days of early autumn.
Growing bulb fennel from seed
If you’ll be growing bulb fennel indoors for later transplanting, you’ll need to start your seeds 4 to 6 weeks before your average last frost date. (For best results, plant in sterile potting mix and use a seedling heat mat.) Expect germination to take about a week.
Now, when growing bulb fennel, it’s important to choose the best type of fennel seed for your climate and the length of your growing season. That’s because high temperatures can cause bolting in your plants. In other words? When things really heat up, your bulb fennel plants will redirect their energy away from developing bulbs and instead put it toward setting blooms and going to seed. Fortunately, Florence fennel varieties like Orion hybrid, Cantino, and Zefa Fino are relatively bolt resistant. Maturing in just 75 days, Dragon fennel is another bolt-resistant variety to consider. (By comparison, the commonly planted Trieste bulb fennel can take up to 90 days to mature.)
When to transplant
Once you have adequately hardened them off, transplant bulb fennel seedlings after the last average frost date for your area. As you plant, try to keep any root disturbance to a minimum, since this can set back their progress. Space your seedlings at least eight inches apart.
How to encourage large bulbs
For large bulbs, consistent watering is key. Check your Florence fennel plants daily to make sure their planting bed hasn’t dried out. The soil should remain moist but not drenched. A good general rule? Provide one to two inches of water each week as needed. I also mulch around the plants with straw or shredded leaves to hold soil moisture and reduce the need to water.
Ensuring that your plants get an adequate amount of nitrogen can also influence bulb size. To give them a lift, you can apply and water in some blood meal or a similarly nitrogen-rich, organic fertilizer.
Growing bulb fennel through the summer
Growing bulb fennel—especially during summer’s high temps and high humidity—can take a little extra diligence and attention to detail. Remember to choose a bulb fennel variety with a maturity window that’s most compatible with the length of your local growing season and water consistently and regularly. Mulching around plants with clean straw or leaf litter will also help to keep the soil cooler and weed growth to a minimum.
How to harvest bulb fennel
Growing bulb fennel is, of course, only half of the equation. How exactly do you harvest the stuff? And when is the very best time to do so?
- Bulbs—Fennel bulbs that look and feel firm and are roughly the size of a large softball (about four inches across) are ready to harvest. Grab the bulb with both hands, gently twist, and pull up to loosen and remove the entire plant from the ground.
- Leaves—You can snip fennel stems and leaves anytime you like. (Just don’t take too many from any one plant as they help to direct energy into your growing bulbs.)
- Pollen and seeds—Place a plastic bag around floral umbels and gently shake their pollen grains into the bag. For green and dried seeds, snip and remove the immature (green) or mature (brown) seed heads, respectively. Make sure dried seeds have completely dried before storing these in an airtight container.
More tips for success
While growing bulb fennel naturally repels slugs and snails, other common garden pests like aphids and cabbage worms are still drawn to it. Regularly check for infestations and hand pick to control small outbreaks. Also, just as common fennel attracts egg-laying swallowtail butterflies, they may find their way to your bulb fennel as well. You can further protect your plants with floating row cover.
The fennel frontier
From sowing fennel seed and encouraging robust plants to harvesting pollen, seeds, and mature bulbs, now you know just what growing bulb fennel takes. Not to be confused with the perennial herb leaf fennel, bulb fennel is typically grown as an annual vegetable and does best in full sun and well-draining soil.
With anywhere from 75 to 90 days to maturity, there are many varieties of bulb (or Florence) fennel available. Again, it’s best to choose bolt-resistant types if you live in a warm climate or are growing into summer. Finally, to help see this cool-weather crop through, water regularly, add a little extra nitrogen during bulb formation, and mulch for root insulation and weed control.
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