Double wave petunias are spreading plants that look great in hanging baskets and large planters, where they will tumble and trail over the edges. They are also used as annual ground covers, spreading to cover an area as large as 4 feet. Petunias are challenging to start from seeds, which are very tiny with approximately 250,000 to 300,000 seeds per ounce. They need light to germinate so they can’t be covered with soil. It takes 10 to 12 weeks to grow petunias large enough to transplant outdoors.
Difficulty: Moderately Challenging
Fill the flat or tray with potting soil. Leave 1/2 to 1 inch of space between the top of the soil and the top of the tray. Firm the soil lightly.
Moisten the soil gently so the water doesn’t leave pits on the soil surface.
Spread the double wave petunia seeds sparingly over the top of the soil. Gently tap them onto the surface, but don’t bury them.
Cover the tray with plastic wrap and set it in a bright, warm location. Keep the tray out of direct sunlight, which can cause the soil to overheat. The seeds need temperatures of 75 to 80 degrees Fahrenheit to germinate, which takes 10 to 12 days, according to the Iowa State University Extension.
Remove the plastic wrap as soon as the seeds germinate. Reduce temperatures to 55 to 65 degrees Fahrenheit.
Place the seedlings so the top of their tray is 4 to 6 inches below a fluorescent light. Set a timer so the seedlings receive 16 to 18 hours of light a day. Adjust the height of the light as the seedlings grow, always maintaining a distance of 4 to 6 inches.
Transplant the seedlings into individual peat or fiber pots when they have three true leaves.
Transplanting Into Pots
Fill peat or fiber pots with potting soil to within 1 inch of the top. Soak the pots in water for a few minutes to thoroughly moisten the pot and the soil.
Allow the pots to drain until the soil is moist but not soggy.
Transplant the seedlings into the pots.
Maintain the potted seedlings under the fluorescent light, just as you did when they were in the tray.
Feed the seedlings weekly with diluted fertilizer.