Prized for their many colors and long flowering period, petunias add bright summer color to beds and containers. A summer annual, petunias grow well throughout the United States, although in northern climates they must be started indoors before being transplanted outside or must be grown from nursery seedlings. Petunias bloom from spring until the first frost kills off the plant, making them a good cover for spring bulb beds after they have stopped blooming.
Prepare a well-drained garden bed in full sunlight after all danger of frost has passed. Apply a 3-inch layer of compost over the garden bed and till it in using a power tiller or hoe to an 8 to 10 inch depth.
Apply 2 lbs. per 100 square feet of a general purpose balanced fertilizer. Work it into the tilled soil and water it well before planting.
Pinch off the top inch of each stem on the petunias before transplanting them into the bed. This encourages branching and creates a fuller, bushier plant.
Plant petunias in the soil to the same depth they were at in their pots. Space the plants 12 inches apart in rows the of the same distance.
Water deeply once a week, providing 2 inches of water per plant. Apply a 2-inch layer of organic mulch over the soil around the petunia plants to aid moisture retention.
Fertilize monthly with a balanced liquid fertilizer. Avoid getting it on the leaves or stems as this may damage the petunias.