Petunias (Petunia spp.) are one of the most popular bedding plants in America. Widely used in landscapes and hanging baskets, they are easy to grow and low maintenance. With blossoms in every color except black and brown, they attract hummingbirds and butterflies. Typically grown as annuals, petunias are only winter hardy in U.S. Department of Agriculture plant hardiness zones 10 and 11. While they have minimal issues with diseases and pests, several potential issues can cause a hardy petunia to die.
Petunias are tolerant of poor soil conditions, drought and heat, but there are some basic requirements that, when left unmet, will lead to problems.
Too Much Shade
Petunias demand a minimum of five to six hours of full sunlight each day. They perform best with all day sun. When placed in a dark or shady location, they stop blooming, and leaves turn yellow.
While they do not require a significant amount of water, petunias cannot stay healthy without good drainage. Ensure the soil is a loamy consistency that drains well. Containers and hanging planters should have at least four drain holes. Petunias in hanging planters must be monitored closely to avoid the soil from becoming overly dry. Watch and water more often if necessary.
If the soil around your petunias is not draining or is clay-like, you will need to amend the soil to save your plants. Add sphagnum moss to the soil using a ratio of 50 percent moss to 50 percent soil. Mix thoroughly and replant your petunias.
If your petunias receive enough sunlight and have well-draining soil and symptoms of wilting, decay or dropping leaves persist, a fungus may be to blame. Phytophthora crown rot and Botrytis fungus are two common microbes that favor petunias. Both can be eradicated with the use of a fungicide. Look for a product labeled "systemic fungicide for ornamental plants."
Mix 4 drops of liquid fungicide concentrate to 1 gallon of water. Spray foliage on both the front and backside of each leaf. Spray all stems down to the soil line. Drench the soil with the fungicide mixture down to the root zone. In 24 hours, apply a ½ inch of water to soil. A second fungicide application to foliage and soil can be repeated in six weeks if necessary.
Can My Petunia Be Saved?
If your petunia went without water for some time and the stems and leaves look dead, the roots may still be alive. Remove the dead leaves and cut the stems down to 4 inches above the soil. Sprinkle the soil with a 12-4-8 all-purpose continuous release plant food. As a general guideline, use 3 tablespoons for a 12-inch container or a 12-inch-wide circumference under a plant, but follow label directions. Do not allow fertilizer granules to touch the stems, and water thoroughly after application. Water as needed to keep the root zone moist. If the roots are viable, new growth will appear within one to two weeks.
If symptoms of disease are affecting the stems of your petunia plant or affecting more than half the plant's foliage, it is unlikely your petunia can recover. Problems occurring in the stem or broadcast en masse over the plant indicate a systemic infection. Destroy the plant and the soil before other plants are infected. Do not reuse the soil or add the plant to a compost pile.