Florence fennel (Foeniculum vulgare var. azoricum) is one of the most aromatic vegetables you can grow—and that’s exactly why companion planting around it can be tricky. After three decades of growing fennel in raised beds and teaching cool-season gardening through UC Extension programs, I’ve learned that fennel behaves differently from most vegetables. It releases natural chemical compounds (allelopathy) that can inhibit nearby plants, especially leafy greens and many root crops.

But that doesn’t mean fennel must grow alone. With the right companions—and smart placement—you can use fennel to benefit your garden while avoiding the species that struggle around it.

Below is an experience-based guide to the best plant partners for Florence fennel and the ones you should keep at a distance.

Table of Contents

Best Companion Plants for Florence Fennel

1. Dill (at a distance or downwind)

Dill and fennel attract many of the same beneficial insects—hoverflies, parasitic wasps, lacewings—but they readily cross-pollinate.
Use case: Plant in the same bed but several feet apart to preserve varietal purity.

2. Calendula

Calendula thrives near fennel and draws pollinators and predatory insects.
My experience: It’s one of the few flowers that performs well even close to fennel’s root zone.

Benefits:

Attracts hoverflies and lady beetles
Tolerates fennel’s aromatic compounds

3. Nasturtium

Nasturtium handles fennel’s allelopathy surprisingly well.
Benefits:

Acts as a trap crop for aphids
Spills lightly through beds without competing heavily

4. Alyssum

Low-growing, beneficial-insect powerhouse.
Why it works: Alyssum’s small root system doesn’t compete with fennel, and it thrives in cool weather.

5. Herbs with Similar Aromatic Chemistry

These thrive because they share some of fennel’s aromatic oils.
Good choices:

Thyme
Oregano
Sage
Rosemary

They don’t seem to be inhibited by fennel’s allelopathy and help attract predatory insects.

6. Strawberries (if spaced correctly)

A surprising but effective companion.
Why it works:

Shallow roots coexist with fennel
Both enjoy loose, fertile soil
Fennel’s scent may help confuse pests

Space them 10–12 inches away for best results.

Plants to Avoid Near Florence Fennel

Based on years of trial, observation, and troubleshooting with gardeners, these crops consistently fail or underperform near fennel.

1. Most Leafy Greens

Spinach, lettuce, and arugula tend to stall out when grown too close.
Reason: Fennel’s allelopathic compounds slow their root development.

2. Beans and Peas

Legumes dislike fennel’s root exudates.
Typical symptoms:

Stunted growth
Low flowering
Yellowing from stress

3. Tomatoes and Nightshades

Tomatoes, peppers, and eggplants are sensitive to fennel’s aromatic competition.
My guidance: Plant them in separate beds.

4. Most Brassicas

Cabbage, broccoli, kale, kohlrabi, cauliflower—nearly all brassicas struggle near fennel.
Why: Brassicas prefer steady, nutrient-rich soil without competition or aromatic interference.

5. Carrots and Other Root Crops

Carrots, parsnips, and beets all respond poorly to fennel’s root zone.
They typically form small or misshapen roots when grown too close.

Where to Plant Fennel Instead

To use fennel effectively and avoid inhibiting neighbors, place it:

At the end of a bed
In a dedicated corner of your garden
Near flowers and herbs that thrive on aromatic complexity
In containers if space is tight

This gives fennel room to develop large, sweet bulbs while supporting beneficial insects throughout your garden.

Final Thoughts

Companion planting with Florence fennel works best when you understand its unique chemistry and growth habits. When paired with flowers and herbs that appreciate its aroma—and kept away from sensitive vegetables—fennel becomes a productive, flavorful, and visually striking part of your cool-season garden.