When to Plant Napa Cabbage in Boulder, Colorado (80310)

Location

Boulder, Colorado

ZIP Code

80310

USDA Zone

Last Frost

Monday, April 20, 2026

📅 Your 2026 Planting Dates

Start Seeds Indoors

Monday, March 9, 2026

Transplant Outdoors

Monday, May 4, 2026

Based on last frost Monday, April 20, 2026 · Zone 6a

Pro tip: Start Napa Cabbage seeds indoors 6 weeks before your last frost date, then transplant outdoors around Monday, May 4, 2026.

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🌿 Plant Details

Scientific Name Brassica rapa subsp. pekinensis

Days to Maturity 70 days

Mature Height 12-18"

Spread 12"

☀️ Growing Requirements

☀️

Sun

Full Sun (6-8 hours)

💧

Water

Regular (1-2 inches/week)

↔️

Spacing

18" apart

🌱

Planting Depth

0.25" deep

Seeds typically germinate in 4-7 days

Ready to Plant Napa Cabbage in Boulder?

Get your seeds now so they're ready by Monday, March 9, 2026.

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🤝 Good Companions

BeetOnionCeleryCucumber

⚠️ Avoid Planting Near

StrawberryTomatoPepper

🤝

Full Companion Planting Guide for Napa Cabbage

See which plants help Napa Cabbage 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

🟡 Moderate

✅ Open-pollinated — seeds grow true to parent

When to Harvest Seed

Allow heads to bolt in spring heat. Harvest seed pods when tan and dry.

Processing

Thresh dried seed stalks, winnow to separate seeds.

Seed Viability

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

Pro Tip

Brassica rapa — crosses with bok choy, turnip, and other rapa crops. Isolate by 300 feet.

🪴

Raised Bed Planting Guides

A 4×8 bed fits 14 plants of Napa Cabbage. See plant counts, spacing grids, and companion pairings for every bed size →

Frequently Asked Questions

When should I plant Napa Cabbage in Boulder, Colorado? +

In Boulder (Zone 6a), start Napa Cabbage seeds indoors around Monday, March 9, 2026 and transplant outdoors around Monday, May 4, 2026.

What is the last frost date for Boulder, Colorado? +

The average last spring frost date for Boulder, Colorado (ZIP 80310) is around Monday, April 20, 2026. This is based on NOAA climate normals for USDA Zone 6a.

How long does Napa Cabbage take to grow? +

Napa Cabbage typically matures in about 70 days from transplanting. In Boulder, that means you can expect harvest around Monday, May 4, 2026 plus 70 days.

Should I start Napa Cabbage indoors or direct sow in Colorado? +

Napa Cabbage should be started indoors 6 weeks before your last frost date. In Boulder, that means starting around Monday, March 9, 2026.

📚 More Napa Cabbage Planting Guides

🗺️

Napa Cabbage in Colorado

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 6a Napa Cabbage Guide

All cities in your zone · Avg dates

→

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Growing Napa Cabbage in Zone 6a

Napa Cabbage (Brassica rapa subsp. pekinensis) is a popular garden vegetable. In Boulder, Colorado, which is in USDA Hardiness Zone 6a, you should start seeds indoors around Monday, March 9, 2026.

Your average last frost date is Monday, April 20, 2026. Plan to transplant your Napa Cabbage seedlings outdoors around Monday, May 4, 2026, about 2 weeks after your last frost date.