Starting Petunias from Seed in Denver: Timing and Techniques

8–10 Weeks Before Last Frost, Under Lights

Petunia seeds need light to germinate, so surface-sow on pre-moistened seed-starting mix. Cover trays with plastic wrap until sprouts appear (7–21 days), then remove immediately.

Light and Air Movement

• Keep seedlings 3–4 inches below grow lights; raise lights as plants grow.
• Run a fan for a couple of hours daily to strengthen stems.
• Pinch tips at 3 inches tall to encourage branching.

Fertilizer and Pest Watch

Don't fertilize until close to outdoor planting time. Hang yellow sticky traps to catch whiteflies and aphids early. Harden off gradually before transplanting after the last frost.