Fennel in Zone 7A — Mountain West

Fennel is an underappreciated gem in the Mountain West garden. Its anise-like flavor shines in salads, soups, and roasted dishes, and the feathery fronds add a delicate touch to any meal. Plus, the cool nights we get even in summer really bring out the sweetness, making your homegrown fennel taste even better than anything you'll find at the store.

Sure, high altitude gardening comes with its challenges – intense sun, alkaline soil, and a short growing season of only about 173 days. But with careful timing and a few tricks, you can absolutely enjoy a bountiful fennel harvest. We'll show you how to work with our unique Mountain climate to grow this delicious and versatile vegetable.

Transplanting fennel isn't generally recommended, as it's prone to bolting when disturbed. However, if you must, aim to get your seedlings in the ground between mid April and mid May.

Before you transplant, be sure to harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Space them 12-18 inches apart to allow for adequate bulb development.

Keep a close eye on the weather forecast. Late frosts are not uncommon during this period in the Mountain West, so be prepared to cover your young plants if temperatures dip unexpectedly.

Direct sowing is the way to go with fennel. It really resents having its roots disturbed. Our short growing season means we need to get seeds in the ground as soon as the soil is workable.

Sow seeds from mid April through late July for a continuous harvest. Choose a spot with full sun and well-drained soil. Fennel prefers a soil temperature of at least 60°F for optimal germination. Before sowing, amend your soil with compost to improve drainage and fertility. Sow seeds about ¼ inch deep and 12-18 inches apart.

Keep the soil consistently moist until seedlings emerge, which usually takes 7-14 days. Thin seedlings to the strongest plant per space once they have a few true leaves.

Fennel needs consistent moisture to develop a nice, plump bulb. But remember, we're in the Mountain West, with our dry climate and intense sun. Finding the right balance is key.

During the spring and early summer, when temperatures are cooler, aim for about 1 inch of water per week. As the summer heat kicks in (and our typical high of 85°F isn't too bad), you might need to increase that to 1.5 inches per week, especially if it hasn't rained. The "finger test" is your friend: stick your finger in the soil about 2 inches deep. If it feels dry, it's time to water.

Water at the base of the plant to avoid wetting the foliage, which can lead to fungal problems in more humid climates. Since we have low humidity, overhead watering isn't a huge concern here, but still try to keep the foliage dry when possible. Signs of underwatering include wilting leaves and slow bulb development. Overwatering can lead to root rot, indicated by yellowing leaves and a mushy bulb.

A good layer of mulch, like straw or wood chips, can help retain moisture and keep the soil cool, which is crucial for preventing bolting in our intense sun.

You can expect your first fennel harvest from late June through mid October, about 65 days after sowing. Keep an eye on those bulbs!

Harvest bulb fennel when the bulb is 3-4 inches across. Don't wait too long, or it can become tough. To harvest, simply cut the bulb at soil level with a sharp knife. The fronds are edible too, and you can harvest them anytime throughout the growing season. Just snip off what you need.

As our first frost approaches in early October, harvest any remaining bulbs, even if they're on the smaller side. They'll still be delicious. You can also cover the plants with a frost blanket to extend the harvest a bit longer.

Fennel can be a bit finicky, but knowing what to watch out for can help you avoid common problems. Here are a few things I've run into in my Mountain garden:

Bolting in Heat

• What it looks like: A tall flower stalk shooting up from the center of the plant. The leaves become tough and bitter, and the bulb stops developing.
• What causes it: Extended warm temperatures, especially if they consistently exceed 80°F. This is a cool-season crop, and our intense sun can trigger bolting.
• How to fix/prevent it: Time your plantings for cooler weather (spring or fall). Choose bolt-resistant varieties. Provide shade during warm spells with shade cloth. Mulch heavily to keep the soil cool. And harvest the bulb as soon as it reaches a usable size.

Allelopathy

• What it looks like: Stunted growth in nearby vegetables.
• What causes it: Fennel releases chemicals into the soil that can inhibit the growth of other plants.
• How to fix/prevent it: Plant fennel away from most other vegetables.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects that thrive in warm weather.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage natural predators like ladybugs and lacewings. Insecticidal soap or neem oil can be used for heavy infestations. Avoid over-fertilizing with nitrogen, as this attracts aphids.

Mountain West Specific Challenges: Our high altitude means more intense UV radiation, which can stress plants. Our dry climate exacerbates bolting if watering isn't consistent. The alkaline soil can also affect nutrient uptake, so be sure to amend with compost regularly.

Companion planting can be a great way to improve your garden's overall health and productivity.

Dill is a fantastic companion for fennel. Dill attracts beneficial insects like hoverflies and lacewings, which prey on aphids and other pests. This natural pest control helps keep your fennel healthy and productive.

Avoid planting fennel near tomatoes, green beans, peppers, or carrots. Fennel inhibits the growth of these plants. It's best to give fennel its own space, away from most other vegetables, due to its allelopathic nature.