When to Plant Petunia in Riverside, California (92521)

Location

Riverside, California

ZIP Code

92521

USDA Zone

10a

Last Frost

Sunday, January 25, 2026

📅 Your 2026 Planting Dates

Start Seeds Indoors

Sunday, November 16, 2025

Transplant Outdoors

Sunday, February 8, 2026

Based on last frost Sunday, January 25, 2026 · Zone 10a

Pro tip: Start Petunia seeds indoors 10 weeks before your last frost date, then transplant outdoors around Sunday, February 8, 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 Riverside?

Get your seeds now so they're ready by Sunday, November 16, 2025.

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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 Riverside, California? +

In Riverside (Zone 10a), start Petunia seeds indoors around Sunday, November 16, 2025 and transplant outdoors around Sunday, February 8, 2026.

What is the last frost date for Riverside, California? +

The average last spring frost date for Riverside, California (ZIP 92521) is around Sunday, January 25, 2026. This is based on NOAA climate normals for USDA Zone 10a.

How long does Petunia take to grow? +

Petunia typically matures in about 75 days from transplanting. In Riverside, that means you can expect harvest around Sunday, February 8, 2026 plus 75 days.

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

Petunia should be started indoors 10 weeks before your last frost date. In Riverside, that means starting around Sunday, November 16, 2025.

📚 More Petunia Planting Guides

🗺️

Petunia in California

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 10a Petunia Guide

All cities in your zone · Avg dates

→

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Growing Petunia in Zone 10a

Petunia (Petunia × hybrida) is a popular garden vegetable. In Riverside, California, which is in USDA Hardiness Zone 10a, you should start seeds indoors around Sunday, November 16, 2025.

Your average last frost date is Sunday, January 25, 2026. Plan to transplant your Petunia seedlings outdoors around Sunday, February 8, 2026, about 2 weeks after your last frost date.