Selecting a Planting Site
A sunny planting site with good soil drainage is key. Besides planting in the garden, raised beds and containers also are options. Fennel should not be planted in the same area as dill or coriander, as cross-pollination can occur and affect the flavor of the seeds. In addition, be sure to take the fennel variety’s mature size into account at planting time, so it doesn’t shade nearby plants. Also, it can inhibit the growth of tomatoes and beans, so avoid planting near either of those crops.
Spacing, Depth, and Support
Plant seeds roughly 1/4 to 1/2 inch deep, and plant nursery starts at the same depth they were growing in their previous pot. Plants should be spaced around 6 to 12 inches apart, and they typically won’t need a support structure.
Fennel Plant Care
Light
Fennel prefers full sunlight, meaning at least six hours of direct sun on most days. Shady conditions will make it leggy and floppy.
Soil
Plant fennel in moist, fertile, well-drained soil. It prefers a slightly acidic soil pH.
Water
Fennel likes evenly moist but not soggy soil. Water whenever the soil feels dry about an inch down, but don’t allow the plant to become waterlogged.
Temperature and Humidity
Fennel is a perennial plant within its growing zones, but gardeners outside of its zones often grow it as an annual. The plant is sensitive to frost and cold temperatures. Plus, hot and dry conditions can cause it to bolt and go to seed. Gardeners in mild climates are sometimes able to plant in the late summer for a fall harvest as long as the temperature remains fairly warm. The plant grows best in temperatures between 60 and 70 degrees Fahrenheit and in moderate humidity levels.
Fertilizer
Fennel generally doesn’t need fertilizer. But it will appreciate compost worked into the soil at the time of planting, along with a layer of compost added around its base every few months during the growing season.
Pollination
Fennel plants are self-pollinators.
Types of Fennel
There are two main types of fennel to grow in your garden, depending on how you plan to use it. Florence fennel (Foeniculum vulgare var. azoricum) is used more like a vegetable, grown for its bulbous stem. The main species plant, common or herb fennel, doesn’t produce much of a bulb and is typically grown for its foliage. Florence fennel cultivars include:
‘Solaris’ produces large, semi-flat bulbs that are resistant to bolting. ‘Zefa fino’ is a large variety that’s ready for harvest in 80 days and is bolt resistant. ‘Orion’ is ready to harvest in 80 days and has large, thick, rounded bulbs with a crisp texture.
Herb fennel varieties include:
‘Dulce’ has an especially sweet flavor.‘Rubrum’ is commonly known as bronze fennel or red fennel for its bronze foliage.
Fennel vs. Dill
At first glance, fennel and dill foliage can look quite similar. The leaves are feathery, bright yellow-green, and branching. However, fennel leaves tend to be longer than those of dill. And the herbs have distinct flavors.
Harvesting Fennel
Harvest fennel leaves as needed throughout the growing season for fresh use. It’s used in both raw and cooked dishes. Frequent harvesting will promote a bushier growth habit and consequently more harvestable foliage. But don’t trim off more than a third of the plant at once. Bulbs can be harvested as soon as the base of the stem becomes swollen. Pull up the plants, and store the bulbs unwashed in the refrigerator for up to five days before use.
How to Grow Fennel in Pots
You can easily grow fennel in containers. In fact, this can be a good option to prevent the plant from self-seeding in your garden where you don’t want it. The container should be at least 10 inches deep with a similar width, and it should have drainage holes. An unglazed clay container is ideal to allow excess soil moisture to escape through its walls.
Pruning
If you wish, you can pinch off flowers as they appear to prevent the plant from going to seed. This keeps the foliage growing and tasting its best for as long as possible. It also stops the plant from freely self-seeding in your garden. However, if you want the seeds for harvesting or self-seeding, allow the flowers to bloom.
Propagating Fennel
Fennel has a long taproot and thus doesn’t divide very easily. The better method is to propagate by seeds. This is both an easy and inexpensive way to get new plants, especially if you live where fennel can only be grown as an annual. Here’s how:
How to Grow Fennel From Seed
Soak seeds in water for a day or two prior to planting to speed up germination. Fennel seeds direct sown in the garden will germinate in a week or two. Keep the soil evenly moist but not soggy as you wait for germination. Seeds also can be started indoors about four weeks before your last projected frost date in the spring under grow lights. Be sure to gradually acclimate indoor seedlings to outdoor conditions before planting them in the garden after the weather warms.
Potting and Repotting Fennel
An all-purpose, well-draining potting mix is typically fine for fennel. For container growth, aim to choose a pot that will accommodate the plant’s mature size right from the start to avoid having to repot. Fennel doesn’t like its roots disturbed. So that means using biodegradable pots for seedlings that can be planted directly in the soil.
Overwintering
If frost is expected in your area, go ahead and harvest the rest of your fennel plant. Otherwise the foliage will likely be damaged or killed. In mild climates, fennel plants can be overwintered for a second growing season, but they usually degrade after that. If unseasonably cold weather is expected in those climates, cover the plants with row covers or another form of protection.
Common Pests and Plant Diseases
Fennel rarely suffers from serious pest or disease problems, though caterpillars might chew on the leaves. This is best handled simply by picking them off the plants by hand. Most often, they are parsley worm caterpillars, which evolve into black swallowtail butterflies, beneficial pollinators for the garden. You can, therefore, choose to ignore these green caterpillars with black and yellow bands if they’re not causing a major issue. Aphids also can sometimes be an issue, but they can be treated by strong sprays of water to dislodge them. Avoid using chemical pesticides on edible herbs. In soil with poor drainage, root rot can occur. If you have heavy soil, try a raised garden bed or container to achieve optimal soil conditions.
