When to Plant Fennel in Honolulu, Hawaii (96813)

Location

Honolulu, Hawaii

ZIP Code

96813

USDA Zone

12b

Last Frost

Thursday, January 1, 2026

📅 Your 2026 Planting Dates

Start Seeds Indoors

Thursday, December 4, 2025

Transplant Outdoors

Thursday, December 18, 2025

Based on last frost Thursday, January 1, 2026 · Zone 12b

Pro tip: Start Fennel seeds indoors 4 weeks before your last frost date, then transplant outdoors around Thursday, December 18, 2025.

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🌿 Plant Details

Scientific Name Foeniculum vulgare

Days to Maturity 80 days

☀️ Growing Requirements

☀️

Sun

Full Sun

💧

Water

Regular

Seeds typically germinate in 7-14 days

Ready to Plant Fennel in Honolulu?

Get your seeds now so they're ready by Thursday, December 4, 2025.

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🤝 Good Companions

Dill

🤝

Full Companion Planting Guide for Fennel

See which plants help Fennel thrive, which to keep away, and raised bed layout tips →

🛠️ Supplies You'll Need

🌱 Seed Starting Trays 🪴 Seed Starting Mix 💡 Grow Lights 🌡️ Heat Mat 🪵 Raised Garden Bed 🌍 Vegetable Garden Soil 🛠️ Hand Trowel Set 🚿 Watering Can

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🌾 Seed Saving Guide

🟢 Easy

✅ Open-pollinated — seeds grow true to parent

When to Harvest Seed

Harvest umbels when seeds turn gray-green to brown — just before they drop.

Processing

Cut seed heads into a bag, dry 1–2 weeks, thresh to separate seeds.

Seed Viability

Up to 4 years when stored cool, dark, and dry.

Pro Tip

Fennel cross-pollinates with dill — keep at least 300 feet apart or sacrifice one crop when saving seed.

Frequently Asked Questions

When should I plant Fennel in Honolulu, Hawaii? +

In Honolulu (Zone 12b), start Fennel seeds indoors around Thursday, December 4, 2025 and transplant outdoors around Thursday, December 18, 2025.

What is the last frost date for Honolulu, Hawaii? +

The average last spring frost date for Honolulu, Hawaii (ZIP 96813) is around Thursday, January 1, 2026. This is based on NOAA climate normals for USDA Zone 12b.

How long does Fennel take to grow? +

Fennel typically matures in about 80 days from transplanting. In Honolulu, that means you can expect harvest around Thursday, December 18, 2025 plus 80 days.

Should I start Fennel indoors or direct sow in Hawaii? +

Fennel should be started indoors 4 weeks before your last frost date. In Honolulu, that means starting around Thursday, December 4, 2025.

📚 More Fennel Planting Guides

🗺️

Fennel in Hawaii

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 12b Fennel Guide

All cities in your zone · Avg dates

→

Other Plants for Honolulu

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Growing Fennel in Zone 12b

Fennel (Foeniculum vulgare) is a popular garden vegetable. In Honolulu, Hawaii, which is in USDA Hardiness Zone 12b, you should start seeds indoors around Thursday, December 4, 2025.

Your average last frost date is Thursday, January 1, 2026. Plan to transplant your Fennel seedlings outdoors around Thursday, December 18, 2025, about -2 weeks after your last frost date.