Considered annuals, petunias grow well in the ground and in containers. Hundreds of petunia varieties are available for the home gardener, with varying colours of pink, red purple and white that complement their light green foliage. Propagated from seeds, petunia plants thrive when grown in containers. Indoor propagation relieves the home gardener of weather and seasonal worries. Petunias grown in containers transition well to the great outdoors in the spring.
Fill a seed-starter container ¾ full with sterile potting soil. Sprinkle the petunia seeds over the tops of each cell. Petunia seeds are very fine and difficult to plant one by one. Sprinkling is a much better option.
Mist the soil to dampen, using a spray bottle filled with water. Keep the soil moist throughout the germination process, which usually lasts 10 to 12 days. Cover the container with a plastic dome. Most seed-starter containers come with the plastic dome as part of the set.
Place the seed-starter container in an area that receives bright, indirect light. Petunia seeds require bright light to germinate. If you do not have access to a window that receives bright, indirect light, place the container under a grow light.
Maintain a temperature between 23.8 and 26.6 degrees C. If you are unable to maintain these temperatures for the petunia seeds as they germinate, place the seed-starter container on a plant heating pad. Adjust the dial on the plant heating pad to the required temperature.
Remove the plastic dome as soon as the petunia seeds sprout. Water the petunia seedlings regularly, keeping the soil moist at all times. Continue providing bright, indirect light and warm 75 to 80 degree F temperatures as the seedlings grow.
Transplant the petunias in 4-inch pots filled with sterile potting soil when they develop their second set of leaves. Plant one petunia plant in each pot. Move the petunia pots outdoors to a sunny location after the final winter thaw.
As the petunias outgrow the 4-inch pots, transplant them into larger planters, hanging pots or window boxes. When planting multiple petunias in large containers, spacing the plants at least 4 to 6 inches apart. Pinch off dead stems and withered blooms with your fingertips. The pinching-off process encourages further blooms. Fertilise the petunias with a 10-10-10 fertiliser. Check the package labelling on the fertiliser for allocation amounts and frequency.
Do not overwater your petunia plants. Keep the soil moist at a 1-inch depth at all times. Press your fingers into the soil before watering. If the soil feels moist 1 inch down, check the soil again in a few days.