The dozens of types of petunias available to home gardeners can act as colorful accent pieces or vigorous ground covers, according to Iowa relatively University. The flowers are also grown as houseplants. Though petunias are typically low-maintenance and hardy, several cultural and disease problems can kill off your petunia collection. Act quickly to fix the problem to preserve the lush beauty and health of your petunia plants.
Poor soil nutrient levels may lead to yellowing of the petunia foliage, and death in severe cases of nutrient deficiencies. Fertilize potted petunias every 14 days with 1/2 oz. of 20-20-20 fertilizer diluted in 1 1/2 gallons of water, according to the University of Rhode Island. For petunias grown in the ground, the university suggests applying 2 lbs. of 5-10-5 fertilizer at the time of planting for every 100 square feet of garden soil.
Petunias require consistent watering or they will wilt and die. Clemson University advises applying 2 inches of water once a week. Using ore frequent and shallow waterings only encourages the petunia plant's roots to linger near the soil surface, making it more susceptible to drought.
Several types of fungi cause powdery mildew on petunias, resulting in foliage that's covered in a film of gray or white dust. Severe fungal infestations can kill the petunia. Minimize your plant's chances of contracting this disease by only applying water at the petunia plant's base, as constantly wet leaves attract fungal growth, according to Cornell University. If drying the plant's leaves doesn't kill off the mildew, apply any one of the many garden fungicides available at most garden stores and nurseries. Example products include those formulated with potassium bicarbonate or sulfur.
Botrytis cinerea creates blight that affects the petunia's blossoms and foliage and, if left untreated, will kill the plant and spread to nearby petunias, according to Cornell University. Immediately trim off any foliage or flowers that are dead and covered in a silver-gray film. Discard the trimmed foliage in a sealed plastic bag to keep the disease spores from spreading. If the entire plant is covered, dig it out before it can infect adjacent plants. Fungicides formulated with chlorothalonil, fixed copper and similar chemicals may help keep the disease from spreading, but their efficacy varies by your region. Consult your regional cooperative extension office (see Resources) for further details on what fungicides perform well against blight in your area.