When to Plant Rhubarb in Honolulu, Hawaii (96821)

Location

Honolulu, Hawaii

ZIP Code

96821

USDA Zone

12b

Last Frost

Thursday, January 1, 2026

📅 Your 2026 Planting Dates

Start Seeds Indoors

Thursday, November 6, 2025

Transplant Outdoors

Thursday, January 15, 2026

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

Pro tip: Start Rhubarb seeds indoors 8 weeks before your last frost date, then transplant outdoors around Thursday, January 15, 2026.

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🌿 Plant Details

Scientific Name Rheum rhabarbarum

Days to Maturity 365 days

☀️ Growing Requirements

☀️

Sun

Full Sun

💧

Water

Regular

Seeds typically germinate in 8-21 days

Ready to Plant Rhubarb in Honolulu?

Get your seeds now so they're ready by Thursday, November 6, 2025.

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🛠️ 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

🟡 Moderate

✅ Open-pollinated — seeds grow true to parent

When to Harvest Seed

Allow flower stalks to develop in early summer. Harvest when seeds in the large seed clusters turn brown.

Processing

Cut dried seed stalks, thresh to release seeds, winnow lightly.

Seed Viability

Up to 3 years when stored cool, dark, and dry.

Pro Tip

Rhubarb seeds don't grow true to variety. For identical plants, propagate by crown division in early spring.

Frequently Asked Questions

When should I plant Rhubarb in Honolulu, Hawaii? +

In Honolulu (Zone 12b), start Rhubarb seeds indoors around Thursday, November 6, 2025 and transplant outdoors around Thursday, January 15, 2026.

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

The average last spring frost date for Honolulu, Hawaii (ZIP 96821) is around Thursday, January 1, 2026. This is based on NOAA climate normals for USDA Zone 12b.

How long does Rhubarb take to grow? +

Rhubarb typically matures in about 365 days from transplanting. In Honolulu, that means you can expect harvest around Thursday, January 15, 2026 plus 365 days.

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

Rhubarb should be started indoors 8 weeks before your last frost date. In Honolulu, that means starting around Thursday, November 6, 2025.

📚 More Rhubarb Planting Guides

🗺️

Rhubarb in Hawaii

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 12b Rhubarb Guide

All cities in your zone · Avg dates

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Growing Rhubarb in Zone 12b

Rhubarb (Rheum rhabarbarum) is a popular garden vegetable. In Honolulu, Hawaii, which is in USDA Hardiness Zone 12b, you should start seeds indoors around Thursday, November 6, 2025.

Your average last frost date is Thursday, January 1, 2026. Plan to transplant your Rhubarb seedlings outdoors around Thursday, January 15, 2026, about 2 weeks after your last frost date.