The bright, nodding blossoms of petunias add vibrant color to summer gardens. These easy-to-grow annuals require little maintenance. They grow in the hot sun, are drought tolerant and aren't too picky about their soil. But if you'd like them to grow extra large or extra fast, etunias need a bit of extra attention.
Pick a variety of petunia know for its large blooms and hearty growth. Try the Grandiflora petunia, with 4- to 5-inch blooms, or the Supertunias, which grow quickly and bloom profusely. The Wave series, introduced in 1995, bloom steadily and grow easily, but their flowers are smaller than other varieties.
Plant your petunias in full sun, meaning at least six hours per day. If they are grown in shade, they will become spindly and not bloom well.
Incorporate a large amount of organic matter such as peat moss, compost and manure into your planting holes. Petunias can be heavy feeders, and this will give them an extra boost when you first plant. The ideal soil pH is between 6.0 and 7.0. Use a soil testing kit from your local nursery or take a sample to your Cooperative Extension to be tested.
Fertilize every two weeks with a balanced fertilizer (10-10-10 or 12-12-12). Also fertilize once in early summer and once in mid-summer with a fertilizer for blooming plants (0-50-30).
Pinch back each stem after the first bloom to 3 or 4 inches long. Deadhead your plants regularly, removing the spent blooms as soon as they die. If your plants become spindly or are producing fewer flowers, prune the stems halfway and fertilize with the balanced fertilizer.
Wash your hands before working with your plants if you smoke or chew tobacco. This will keep the tobacco mosaic virus from entering your garden. The virus can cause petunia leaves to become yellow-green and deformed.
Water from below with a soaker hose or a watering can with a long spout. Petunia flowers will close up when wet and not open again for several days.