Petunias are a brightly-colored annual that does well in both gardens and containers, including pots, window boxes and hanging baskets. They fill the air with their heavy scent and produce large trumpet-shaped blooms. Petunias are fairly easy to grow and care for. Start your petunias from seed indoors and transplant the seedlings outside when it is warm. With a little upkeep, you can keep your petunias blooming from spring to first fall frost.
Fill a flat container, about the size of a cookie sheet, with potting soil or sphagnum moss. Sprinkle the seeds lightly on top of the soil. Mist the soil with water to help the seeds wash into the potting soil. Lightly press the seeds into the soil.
Cover the container with a clear plastic lid and place them in a warm location — about 75 to 80 degrees Fahrenheit — out of direct sunlight. Leave the container in this area until you start to see seedlings emerge, which usually takes about seven to 10 days.
Remove the lid and place the container in a location that is brighter, but cooler — the temperature should be about 65 degrees during the day and between 55 and 65 degrees at night. Place the seedlings 4 to 6 inches below a fluorescent light, for best results. Place the lights on a timer so that the seedlings receive about 16 to 18 hours of light a day. Raise the lights as the petunias grow taller. Mist the soil with water whenever it appears dry.
Transfer the seedlings to individual peat pots or packs when they have three true leaves. Give them diluted fertilizer every two weeks and take them outside during the day to help them get used to the temperature change. Bring them indoors at night.
Transplant the petunias outdoors when the soil is about 60 degrees F and the threat of frost is gone. Choose a location that receives full sun and has well-drained soil. Dig a hole in the ground that is about twice the size of the roots and then completely cover the roots with the soil. Water the plant immediately, then whenever the soil appears to be dry.
Remove dead or faded flowers from your petunias by pinching them off with your fingers. Doing so will encourage new growth.