Initially place plants in a shady, protected area and then gradually expose them to direct sun. Bring them indoors at night if freezing temperature are predicted. Planting Petunias can be transplanted into the garden after the danger of frost has passed. In central Iowa, the last frost usually occurs around May 5-10. Petunias are easy to grow if a few requirements are met.
Petunias perform best in sunny locations.
They also require a moderately fertile, well-drained soil. Poorly drained soils can often be improved by incorporating organic matter, such as compost, peat, or well-rotted manure. Plant petunias about 12 inches apart. Pinch back grandifloras and multifloras to encourage branching. Pinching is especially helpful for tall, leggy plants.