9 Tips for Growing Great Fennel

Fennel is a versatile root vegetable and herb that can be grown in both spring and fall for a delicious harvest.

by Jesse Frost

Whether shaved into a salad in the early summer or roasted with rosemary in the fall, fennel is a versatile and attractive vegetable to grow—especially because it’s not just a vegetable. The fronds are a great anise-flavored herb, the seeds are a wonderful spice known for their digestive properties, and the flower is a pollinator-attracting powerhouse and lovely addition to any bouquet. So naturally, there’s significant incentive to grow fennel for both home use and the market table.

What does it take to grow great fennel? It’s definitely not your average crop, but it’s also not the most difficult plant to grow either. Don’t be intimidated if you’re a beginning gardener. If you can put a little extra work into your soil, you, too, can grow great fennel. Here are some tips to make the job a little easier.

1. Know Your Purpose When Selecting Seed

Fennel seed can be found in both the vegetable and herb sections of many seed catalogs. When making your choice, read the description thoroughly to ensure you’re getting the right variety for your growing zone and preferred use. Bronze fennel, for example, is intended solely for the fronds and flowers and does not make a real bulb, while good bulb varieties include Solaris, Orion and Florence. High Mowing Seeds has variety called Preludio, which is said to be bolt-resistant—good for growing in the spring and summer. If you have a favorite Italian seed purveyor, that is another ideal place to check out.

2. Feed Your Soil

Fennel Growing Tips
Alice Henneman/Flickr

Well-drained and fertile soil is optimal for most crops, but especially for fennel. It needs fertile soil high in organic matter to produce a sizable bulb, and few things enrich soil and add humus quite like well-made compost. Fennel also needs a fair bit of water, so if you’re going to irrigate just one crop, this is it. Irrigating will help encourage a larger bulb while discouraging the plant from bolting. Don’t overlook the desired pH, either: Fennel likes neutral soil between 6.5 and 7.5. Perform a soil test and amend your soil as needed to fit these requirements.

3. Avoid Extreme Temperatures

If you are hoping for good spring/summer fennel, you will need to start the plants indoors four to five weeks before your last frost date. While fennel is fairly hardy and can take several light frosts, it will not likely survive a hard one, so transplant the young seedlings after last chance of hard frost has passed. On the flip side, get your plants in the ground early enough that they have time to mature before the heat of summer. In cooler climates, there isn’t as much of a rush, but in the South, the long, hot days can encourage the fennel to bolt before it’s fully mature. In general, fennel needs a good amount of sunlight, but for a solid spring crop, consider planting near sweet corn or another tall crop so that when the sun is more intense, the fennel receives a small amount of shade.

4. Plan For A Fall Harvest

Fennel is not a great vegetable for storing, so it makes sense to spread out your harvest via succession planting. Sow seeds directly into the garden 1 inch apart and 1/4 inch deep during the summer for a fall harvest. Like carrots, fennel takes several days to germinate and can be swallowed by weeds if planted into uncultivated soil, so prepare those beds well before sowing. You can also sow or start seeds in soil blocks around the time you would be sowing your fall crops like cauliflower and Brussels sprouts—90 days or so before you wish to harvest. As with your spring crop, keep it watered and well-cultivated to produce the best bulbs.

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5. Mulch Established Plants

When you’re cultivating around fennel, be careful not to disturb the roots with your hoe or cultivator, as it may cause the plant to bolt. With that in mind, it wouldn’t be a bad idea to mulch your fennel once it’s established to retain moisture and fight off weeds—two important requirements for good fennel.

6. Do Not Use It As A Companion Plant

Because fennel is a heavy feeder, it isn’t known for being a particularly beneficial companion crop. In the classic book Carrots Love Tomatoes (Storey Publishing, 1998), author Louise Riotte states soberly, “Most plants dislike fennel.” She even goes on to add fennel has an “inhibiting effect” on bush beans, tomatoes and kohlrabi. To avoid a disappointing growing season next year, renew the soil with good compost after harvesting fennel and rotate your fennel plantings away from the aforementioned crops where possible.

7. Let The Flowers Grow

Fennel Growing Tips
John Tann/Flickr

Because fennel flowers attract many beneficial insects, fennel can be a valuable cut flower to have in the garden. It’s not known for being a pest magnet, and as Pam Dawling notes on GrowingForMarket.com, “You might find aphids or whiteflies on the leaves, but they are rarely a serious problem.”

8. Plant In Well-Drained Soil

The main disease fennel suffers from is root rot, which can be avoided with well-drained soil. So, water often, but make sure the water can drain away. If your soil has poor drainage, consider making small raised beds for the fennel or adding equal parts sand, peat moss and compost to the area of the garden where you plan to plant. With good drainage, fennel tends to be a rather robust crop.

9. How To Harvest

Harvest fennel when the bulbs are roughly 3 inches wide. With a sharp knife or pruners, cut the bulb free of the tap root and clean up any withered or brown fronds. You can cut the rest of the fronds a couple inches above the bulb if you would like, but some growers prefer leaving the fronds on for market. If you do this, keep fronds misted and cool: Like dill, they will readily wilt. Fennel keeps in the refrigerator for up to a week, but it should be used up rather quickly.

No matter why you choose to grow fennel, it can be a valuable and delicious crop for you, your farmers market customers and your local pollinators.

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