By Pam Dawling. Pam is the garden manager at Twin Oaks Community in central Virginia. Her book, Sustainable Market Farming: Intensive Vegetable Production on a Few Acres, is available from Growing for Market. Subscribers always get 20% off books when they are logged in. Pam's blog is at sustainablemarketfarming.com.
This article originally ran in the April 2013 issue of Growing for Market Magazine.
Many people grow fennel as the herb, for leaves and seeds, for salads, soups, fish dishes and teas. The seeds are also used in desserts, breads, other baked goods and drinks. Or they are chewed after a meal to help the digestion. A newer crop in the U.S. is bulb fennel, with a vaguely licorice-like flavor. The crunchy white “bulb” consists of the swollen stem bases of the leaves. Fennel is also used in the seedling stage as a microgreen or baby salad mix ingredient. And even newer and more “exotic” is fennel pollen. Although this crop is used in so many forms, the basic details are the same for all types, so I’ll start with those.
Bulb fennel on display at a farmers market. Photo by Nikki Warner.
Fennel benefits from a rich, well-drained soil, with a pH of 5.5-6.8. Plant in a sunny spot for best results. Bear in mind that fennel is a Mediterranean crop, a cool-weather short-lived perennial normally grown as an annual. Fennel survives light frosts, but will only survive over winter outdoors (assuming you didn’t harvest the bulb) in zones 6-10. In zones 2-5 it grows as a biennial. It tolerates some heat and cold, but does best when it reaches maturity in cool weather. Depending on your climate, seed may be sown in early spring, mid-spring, late summer and early fall. Fennel grown for bulbs will not provide seed too – to get succulent bulbs, grow the plant fast, harvest before flower stems form and provide plenty of water. If water is in short supply, put bulb fennel at the top of your watering list.
There are about 200 seeds per gram, 7,000 seeds per ounce. The average direct seeding rate is 1000 seeds/100', 700'/ounce, or an average of 4,000 transplants/ounce of seed. Each diner could eat up to five fennel bulbs over a season.
Fennel is not troubled by many insect pests or diseases. You might find aphids or whiteflies on the leaves, but they are rarely a serious problem. Slugs can be trouble. The worst disease is root rot, which can happen if your plants get waterlogged for too long. I’ve been emphasizing the importance of enough irrigation, but don’t over-water!
To germinate fennel successfully, the seeds must be in the dark, with a soil temperature of 60-90°F. (70°F is ideal.) Direct seed at 10 seeds/ft, in rows 18" apart. Thin the seedlings to 6-12" apart. Or station sow the seed, dropping three seeds together at 12” intervals along the row, later thinning to leave the strongest seedling at each station. If the soil is dry when you are sowing, soak the furrow first. Cover the seeds with 1/8-1/2” of soil. They will take about 7-10 days to emerge. To improve germination, try soaking and pre-sprouting the seed for several days.
Bulb fennel can be sown outdoors as early as 2-5 weeks before the average last frost date in spring, but when the danger of hard frost (28°F) is over. Beware - early spring sowings are more likely to bolt. Bulb fennel is sensitive not only to day-length, but it may also bolt if there is a sudden chill (a temperature reversal). Here in zone 7, we sow Zefa Fino March 10, for April 10-26 transplanting, along an edge of a bed with parsnips, celery and (later) asparagus beans. The transplanting date is around our last frost date. If your climate and timing give you the choice, direct sow and thin, rather than transplanting, to reduce the likelihood of bolting.
The best time to sow bulb fennel is for an autumn crop. Sow in mid- to late-summer, calculating the sowing date by working back from your hoped-for harvest date. Your last sowing date will be 90-110 days before your first fall frost. In northern latitudes, gardeners wait till the summer solstice to sow any bulb fennel. If you sow around the middle of June, you should be harvesting bulbs in mid-October. The bulbs can survive a frost or two, so there is no rush to harvest when cold weather arrives. We aim to direct sow on July 8, and July 28, in part of a carrot bed. This way we keep the fennel with its umbelliferae cousins, and make our crop rotation easier.
Transplanting is useful in areas with short springs, or short seasons overall. Fennel is said to dislike root disturbance, so if transplanting, use plugs or modules. Sow 3 seeds/cell, 1/4" deep, in 1.5-2" deep cells. Thin to 1 plant/cell. Transplant outdoors in mid-spring to late summer when plants are 3-4” tall, and 4-6 weeks old, before they become root-bound, and when they can be removed easily without disturbing the roots. Final spacing should be 6-12” apart, either in single rows, or in rows 18” apart. Do not crowd bulb fennel plants, especially in spring, or you will encourage bolting. The plants will grow 36” tall or more, and the stems and delicate foliage can be eaten or made into teas. Herb fennel may grow to 60”.
Varieties of bulb fennel
For fennel bulbs, also known as finocchio, or Florence Fennel, sowings after mid-summer have a better chance than spring ones of producing fat tender juicy bulbs, partly due to wetter weather as the bulbs mature, and partly as they do not having lengthening daylight to induce bolting.
For earliness, try Montebianco (mid-size round white bulb, solid stalks), Mantovano, (75-85 days, round very white large bulbs), or Parma Sel Prado, (round white smallish bulbs). All from Seeds from Italy.
Some varieties do much better in the fall: try Mantovano, Bianco Perfezione Sel Fano (80-85 days, good size, half-hollow stem) from Seeds from Italy, or Victorio (75 days) from Territorial Seeds.
For spring as well as fall, try Romanesco, (85 days, a large classic variety with thick tightly wrapped stems), generic Florence Fennel (90 days), Zefa Fino (80 days) or Trieste (90 days), a bolt-resistant hybrid from Renee's Garden.
Zefa Fino is more tolerant of stress than some of the traditional Italian varieties, so if your climate or timing is borderline, try this one.
Preludio and Orazio (both 80 days) are F1 hybrids from Johnny’s Selected Seeds, that have a higher yield potential than open pollinated fennels. (All the others I have mentioned, except Trieste, are OPs)
For cooler climates, try Victorio.
The two seasons for planting bulb fennel in zone 7 are March-April and July-August – the same dates that work for broccoli, beets and other cool weather crops. Bulb fennel is a seasonal treat that can be harvested for several weeks, but it is not a year-round vegetable in most climates. It is hardy to 15°F. If bulb fennel is new crop for you, experiment with several varieties and with sowing dates that match your other cool weather crops. The fall crop is likely to be more successful than a spring one. If your spring crop bolts before forming a good bulb, the feedback is that your weather is too hot for spring planting, so stick to fall crops in future, unless you can safely start earlier in the spring.
Bulb fennel vareities put more of their energy into the bulb than the leaves or flowers, and should be used when the bulb is what will be marketed.
Rich, well-drained soil, regularly irrigated, and cool temperatures produce top quality bulbs. Plants grow best and the flavors are superior when daytime air temperatures are 60-70°F. Start to blanch the lower stems when the bulb is the size of an egg by hilling up soil around the bulb. Mulching (with organic materials such as straw or hay) can be a good strategy to trap soil moisture and cooler temperatures in spring – the bulbs will be sweeter and more tender. Clip off any seed stalks that start to grow. The bulbs will be ready about three weeks after reaching egg size.
Harvest and postharvest
The bulbs are harvested when they get to small tennis ball size. If you leave them to grow larger, the plants will probably bolt and the flavor of the bulbs will quickly become bitter. Use a sharp knife or pruners to cut the bulb free just above taproot, right at the soil line. Trim the leaf stems about 1-2" above the bulb to prepare it for sale or storage. Bulb fennel requires 80-115 frost-free days to reach harvest.
Bulb fennel will keep in the refrigerator up to 1 week or in a cold moist place for 2 to 3 months. Best storage conditions are 32°F with 95% relative humidity. Stalks can be dried or frozen; leaves can be frozen or dried as herbs. Dried leaves should be stored in an airtight container.
For more on postharvest handling for a variety of vegetables, read our article "Beat the heat in postharvest handling."
Nutrition and cooking
Bulb fennel is high in vitamin C, and is also a good source of calcium, fiber and potassium. According to Southern Exposure Seed Exchange www.southernexposure.com, medicinally, fennel stimulates digestion while reducing the likelihood of flatulence. It is anti-spasmodic and anti-inflammatory. It can be used to soothe bronchial coughs in the same way that dill can. It has estrogenic properties to stimulate milk flow in nursing mothers.
Because it is an uncommon crop in this country, it is probably wise to offer your customers some guidelines on how to prepare and eat it. Fennel bulbs can be eaten raw, sliced thin, in salads or with dips. They are good grilled, sautéed, or steamed whole or sliced. They are delicious boiled and served with cheese sauce or butter. Try roasting with olive oil.
Fennel plants are attractive to butterflies, ladybugs, lacewings and pollinators. They can grow to 5’ tall, so plan accordingly. Herb fennels will not produce bulbs. Seeds may be direct sown or transplanted, as for bulb fennel. The color of the small seedlings of bronze fennel renders them almost invisible, so take care when weeding. Bronze fennel has thin stems and beautiful bronze feathery foliage, good for flower arrangements as well as salads and plate décor. It takes about 65 days from sowing to harvestable size. The green leaf type is even easier and up to ten days quicker to grow. Johnny’s sells a green and bronze mix. Fennel can be overwintered in mild areas (Zones 7-10) to provide seed the second summer.
The feathery foliage has a sweet anise flavor and is a tasty addition to salads, cole slaw, and dressings. To dry the leaves, bunch them and hang in a dry well-ventilated area – good air circulation is essential for success. Check the leaves for dryness once a week, for two to four weeks, until they are brittle, then crumble and store in a cool dark place.
Varieties of fennel that put more of their energy into making leaves and flowers are called leaf or herb fennel, and should be used instead of bulb fennel if bunches of leaves or flowers are the desired end product. Of course you can still use the leaves and flowers from bulb fennel in a pinch, bulb fennel just won't make as many of the aerial parts of the plant as leaf or herb fennel.
Fennel seeds are used in teas and tinctures as a digestive aid, expectorant, and a tonic for the spleen, kidneys, and reproductive system. For seeds, try Finocchio Selvatico — Wild Fennel (75 days) from Seeds from Italy, www.growitalian.com. The seeds are superior to those of cultivated varieties, and the flowers are beautiful too. Johnny’s warns that too much moisture at bloom time can prevent the formation of a good crop of seeds. The seeds shed very easily, and you may not want a zillion fennel plants next year, so consider tying paper or cloth bags over the heads, before they shed.
To dry fennel seeds, wait for the flowers to turn brown. Spread the freshly gathered seeds (plump and grey-green) in a single layer on a horizontal window screen. Keep mice away. The seeds should be fully dry (and brown-green in color) in about two weeks. Store in a cool dry place.
Fennel does not cross with anything except other fennel. It is widely said (even by some seed companies!) that dill and fennel cross, and some even describe the terrible flavor of the resulting crosses.
Microgreens and flowers
The feathery seedlings make an attractive ingredient for microgreen mixes and plate garnishes. Johnny’s sells a special variety called Grosfruchtiger for microgreens, although any kind can be used. For more on microgreens, read our article "How to grow microgreens."
In addition to producing pollen, fennel flowers come in small clusters that many beneficial insects like ladybugs like to feed upon.
Fennel pollen has recently been rediscovered as a flavor enhancer. Only a sprinkling is needed. It sells for $15/ounce, and is sometimes sold combined with salt. If you have the market, or can create it, why not try growing and collecting your own?
In places like California where fennel is invasive and now grows wild, it might be possible to source fennel pollen from feral patches, instead of letting it go to flower on your farm. On the other hand, there's a pretty good chance that if you grow fennel on your farm, it will go to seed at some point, and here's how to harvest it.
Cut the fennel flower stems at 6-8”, bundle and tie 15-20 together. Cover the heads with paper bags leaving about 1” of stem sticking out of the bags. Tie the bags closed and hang them in a cool, dark and dry area with the stems pointing up. Use fans if needed. Tap the sides of the bags every couple of days for two weeks as the flowers dry.
When the flowers seem dry, shake the bag vigorously. Carefully open the bags and untie the bundles. Tap each individual flower head on the side of the bag as you remove it. Tip the fennel pollen and other plant matter from the bag into a fine mesh strainer resting over a bowl or bucket. Sift the pollen through the sieve, to remove the other plant matter and the larger tiny wildlife. If you need to kill any teeny tiny wildlife, you can microwave the pollen for 10 seconds.
Each flower head will produce about 1/4 tsp. of pollen. Collecting one ounce can take an hour, so a selling price of $15 suddenly doesn’t seem outrageous. Store the pollen in an air-tight container in a cool dark place. For maximum flavor, use within a year of collection.