How Long It Takes to Grow Petunia Flowers

Starting Seeds

• Petunia seeds are fine and best handled with a commercial seed planter or homemade planter consisting of an envelope or small piece of folded paper. Sprinkle seeds on top of a lightweight seed-starting mixture such as peat moss and vermiculite and do not cover. Petunias need light for germination so place them in a sunny window or use an outdoor greenhouse or cold frame. Mist with water until the soil is moist and cover. Commercial window greenhouse kits often come with a clear plastic cover, but plastic wrap can create the same warm, moist environment. Start seeds eight to 10 weeks before the end of frost in your area.

Caring for Seedlings

• Petunias grow best in warm weather where air and soil temperatures reach the upper 60s or 70s degrees Fahrenheit. When forcing seeds inside before frost, you need to simulate that environment by minimizing the amount of time that seeds and seedlings are exposed outside of the artificial environment created by your greenhouse. Water will contine to cycle through the greenhouse if the top is not removed, as evident by the condensation that collects on the clear plastic. Inspect emerging seedlings without removing the lid.

Growing Seedlings

• Once seedlings have sprouted, thin them out, leaving one strong seedling centered in your container (or space them 2 inches apart if you're using a large container.) Re-cover after thinning and continue to inspect regularly for any needed extra watering. Turn the container daily if you notice seedlings starting to lean too far one direction in need of sunlight. Once your seedlings can reach the cover, remove the cover. Leaves left to linger against plastic can start to rot from the excess moisture. Water regularly to keep the soil moist.

Preparing to Transplant

• Petunias, like any warm-season plant started indoors, need to be transitioned outdoors before transplanting to avoid potential shock to the system. As the end of frost season draws near, move petunias started indoors to a covered porch or open cold frame for a few hours during the day. Bring seedlings back indoors for the night. Do this for a few days before leaving the seedlings outdoors overnight after the threat of frost has passed. After frost, your petunias should be ready for transplanting to containers or beds. For better results, remove the first few blooms from the plant to force the plant to continue to grow before allowing it to bloom. You'll have a fuller plant with more blooms later in the summer.

Caring for Petunias

• Petunias have a single-season life cycle but can give quite a show if watered, fertilized and cared for properly. Consider purchasing seedlings at the beginning of the season if you didn't get a two-month jump on starting seeds indoors for the longest amount of life. Depending on the variety you choose, petunias will continue to spread and grow until frost. Deadhead petunias regularly to keep the blooms coming for the duration of the season. Annuals that have spent blooms removed will expend their energy in bloom production. In midsummer, trim back varieties that are starting to look leggy and scraggly to invigorate bloom production as well.