Fennel in Zone 6B — Midwest

Fennel's mild anise flavor adds a unique twist to Midwest dishes, from salads to grilled meats. The feathery fronds are as delicious as the bulb, offering an extended harvest. Plus, it’s incredibly satisfying to pull a plump fennel bulb from our fertile soil.

Our Midwest weather can be unpredictable, with warm spells in spring and summer heat spells that can stress cool-season crops. But with a little planning, you can easily enjoy fennel within our 183-day growing season. Timing is key.

Transplanting fennel isn't generally recommended, as it can bolt easily. Direct sowing is the preferred method. But if you must transplant, do so from mid-April through mid-May.

Harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade, increasing the time and sun exposure each day. Space the transplants 12-18 inches apart.

Keep an eye on the Midwest weather forecast at transplant time. Be prepared to protect young plants from unexpected late frosts with row covers or blankets.

Direct sowing is the way to go with fennel. The taproot doesn't like being disturbed, and transplanting can trigger bolting. Sow directly into the garden mid-April through late July.

Prepare a sunny spot with well-drained soil. Aim for a soil temperature of at least 50°F. Sow seeds about ¼ inch deep and 12-18 inches apart.

Keep the soil consistently moist until seedlings emerge, which usually takes about a week. Thin to one plant per spacing once they are a few inches tall.

Fennel needs consistent moisture, especially during bulb development. But because we often have wet summers here in the Midwest, it’s a balancing act. Too little water, and you'll get tough, stringy bulbs and bolting. Too much, and you risk root rot in our sometimes heavy clay soil.

In the spring and fall, when temperatures are cooler and rainfall is more frequent, you might only need to supplement with an inch of water per week if the rain isn't doing the job. During our summer heat spells, increase that to 1.5-2 inches per week, delivered in one or two deep soakings. Stick your finger about 2 inches into the soil. If it feels dry, it's time to water.

Water at the base of the plant to avoid wetting the foliage. With our moderate-to-humid summers, overhead watering can encourage fungal diseases. Signs of underwatering include wilting and yellowing leaves. Overwatering can cause yellowing leaves, stunted growth, and potentially root rot.

Mulch around your fennel plants with straw or wood chips. This will help retain moisture, suppress weeds, and keep the soil cooler during those summer heat spells.

You can expect your first fennel harvest from mid-June through late October, depending on when you sowed your seeds. Fennel is usually ready to harvest about 65 days after sowing.

Harvest bulb fennel when the bulb is 3-4 inches across. Don't wait too long, or it can become tough. Simply cut the bulb at soil level with a sharp knife. The feathery fronds are edible and can be harvested anytime throughout the growing season.

As our first frost approaches in mid-October, harvest any remaining bulbs, even if they are on the smaller side. The fronds can be chopped and frozen for later use.

Here are three common problems you might encounter with fennel in the Midwest: bolting in heat, allelopathy with most vegetables, and aphids.

Bolting in Heat

• What it looks like: A tall flower stalk emerges from the center of the plant. The bulb becomes smaller, and the leaves taste bitter.
• What causes it: Extended warm temperatures above 80°F trigger bolting. Our summer heat spells are a prime culprit.
• How to fix/prevent it: Time your plantings for cooler weather in spring and fall. Choose bolt-resistant varieties if available. Provide shade with row covers during warm spells. Mulch to keep the soil cool. Harvest fennel before bolting progresses too far.

Allelopathy with Most Vegetables

• What it looks like: Stunted growth and poor yields in nearby plants.
• What causes it: Fennel releases chemicals into the soil that inhibit the growth of many other vegetables.
• How to fix/prevent it: Plant fennel in a dedicated area away from most other vegetables. Consider growing it in containers.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Knock them off with a strong spray of water. Encourage ladybugs and lacewings (natural predators). Use insecticidal soap for heavy infestations. Neem oil also works. Avoid excess nitrogen fertilizer.

Midwest Specific Challenges: Our moderate-to-hot summers and moderate-to-humid humidity can make fennel prone to bolting and fungal diseases. Careful watering and timely harvesting are key to success. The wet-summer rainfall means you have to watch for root rot in our sometimes heavy clay soil.

Dill is a good companion for fennel because it attracts beneficial insects like ladybugs and hoverflies, which prey on aphids.

Avoid planting fennel near tomatoes, beans-green, pepper, or carrots. Fennel inhibits their growth due to allelopathy. Keeping fennel separate from these plants will improve their yields in your Midwest garden.