Petunias are one of the most popular annual flowers for backyard gardeners, according to the University of Minnesota. People prize them for their low maintenance, fast growth, bright colors and pleasant fragrance. Occasional cultural, disease and insect problems may still arise while growing this hardy plant.
Though they're relatively drought hardy, petunias need occasional watering to keep the plant hydrated and prevent wilting of the plant's foliage and blossoms. The University of Iowa recommends watering petunias grown in the ground once a week. Use enough water to moisten the soil to a depth of 6 to 8 inches, according to the University of Minnesota. The university suggests checking container-grown petunias more regularly as container soil often dries out quickly. Water whenever the top 1 to 2 inches of potting mix feels dry.
Use too much fertilizer and you'll cause excessive foliage development at the expense of flower production, according to the University of Rhode Island. Use too little, and your plants may not experience optimal growth rates. The university recommends spreading 1 pound of 5-10-5 fertilizer for every 50 square feet of garden soil at the time of planting, then a half-pound for every 50 square feet in mid-summer.
Poor Plant Density
Petunias need encouragement to develop a dense and bushy shape. Once they're 6 inches high, the University of Minnesota says gardeners should pinch off their growing tips. This encourages the petunias to produce side shoots, creating more foliage and more flowering.
Spider mites are relatively common. They may appear throughout the petunia foliage and experience a population explosion in the heat of summer. If left untreated, the afflicted petunias will wilt and experience widespread foliage loss. Shooting down the petunias with water helps remove dust, which attracts the mites, according to the University of California. A standard houseplant or garden insecticide formulated with carbaryl will effectively kill off the insects.
If your petunias are kept too moist for too long, they may become overgrown with a fungal disease known as powdery mildew. The mildew leaves a white dust across the petunia blossoms and leaves. Minimize risks by keeping your petunia plants' foliage dry and only watering the plant at its base, instead of overhead. The University of California recommends fungicides formulated with neem oil or horticultural oils if drying the plant doesn't kill off the disease.