When to Plant Petunia in Arlington, Colorado (81021)

Location

Arlington, Colorado

ZIP Code

81021

USDA Zone

Last Frost

Saturday, April 25, 2026

📅 Your 2026 Planting Dates

Start Seeds Indoors

Saturday, February 14, 2026

Transplant Outdoors

Saturday, May 9, 2026

Based on last frost Saturday, April 25, 2026 · Zone 5b

Pro tip: Start Petunia seeds indoors 10 weeks before your last frost date, then transplant outdoors around Saturday, May 9, 2026.

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🌿 Plant Details

Scientific Name Petunia × hybrida

Days to Maturity 75 days

Mature Height 6-18"

Spread 18"

Type Annual

☀️ Growing Requirements

☀️

Sun

Full Sun (6-8 hours)

💧

Water

Moderate (1 inch/week)

↔️

Spacing

12" apart

🌱

Planting Depth

0.13" deep

Seeds typically germinate in 7-14 days

Ready to Plant Petunia in Arlington?

Get your seeds now so they're ready by Saturday, February 14, 2026.

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🤝 Good Companions

TomatoBasilMarigold

⚠️ Avoid Planting Near

Fennel

🤝

Full Companion Planting Guide for Petunia

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

🛠️ Supplies You'll Need

🌱 Seed Starting Trays 🪴 Seed Starting Mix 💡 Grow Lights 🌡️ Heat Mat 🌍 Flower Garden Soil ✂️ Pruning Shears 🚿 Watering Can

* Affiliate links — we may earn a small commission at no extra cost to you.

🌾 Seed Saving Guide

🟡 Moderate

⚠️ Many varieties are F1 hybrid — look for OP/heirloom types

When to Harvest Seed

Allow seed pods to form after flowers fade. Harvest when the small pod turns tan and begins to split.

Processing

Collect tiny seeds in a bowl when pod splits, dry 1 week before storing.

Seed Viability

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

Pro Tip

Most petunias are F1 hybrids — seedlings will not match the parent. Look for OP/heirloom varieties for reliable seed.

🪴

Raised Bed Planting Guides

A 4×8 bed fits 32 plants of Petunia. See plant counts, spacing grids, and companion pairings for every bed size →

Frequently Asked Questions

When should I plant Petunia in Arlington, Colorado? +

In Arlington (Zone 5b), start Petunia seeds indoors around Saturday, February 14, 2026 and transplant outdoors around Saturday, May 9, 2026.

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

The average last spring frost date for Arlington, Colorado (ZIP 81021) is around Saturday, April 25, 2026. This is based on NOAA climate normals for USDA Zone 5b.

How long does Petunia take to grow? +

Petunia typically matures in about 75 days from transplanting. In Arlington, that means you can expect harvest around Saturday, May 9, 2026 plus 75 days.

Should I start Petunia indoors or direct sow in Colorado? +

Petunia should be started indoors 10 weeks before your last frost date. In Arlington, that means starting around Saturday, February 14, 2026.

📚 More Petunia Planting Guides

🗺️

Petunia in Colorado

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 5b Petunia Guide

All cities in your zone · Avg dates

→

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Growing Petunia in Zone 5b

Petunia (Petunia × hybrida) is a popular garden vegetable. In Arlington, Colorado, which is in USDA Hardiness Zone 5b, you should start seeds indoors around Saturday, February 14, 2026.

Your average last frost date is Saturday, April 25, 2026. Plan to transplant your Petunia seedlings outdoors around Saturday, May 9, 2026, about 2 weeks after your last frost date.