Petunias are staples of many annual beds. With their versatile colors, ranging from white to deep purple, to their ability to quickly cover a wide area, they are generally an easy plant to grow. Basic care, including regular watering only if there's little rainfall, and little weeding, makes them environmentally friendly commercial annuals, requiring fewer resources to grow than more delicate plants. Feeding petunias helps ensure they remain pest free and vibrant.
Ideal Fertilizer for Petunias
Petunias require a fertilizer high in phosphorus to produce large amounts of healthy flowers. Fertilize with 10 parts of nitrogen and potassium for every 20 parts of phosphorus -- double the amount of phosphorus than either other nutrient -- to ensure sufficient phosphorus, while still maintaining adequate amounts of nitrogen and potassium. Fertilizer mix is labeled with the proportions of nitrogen, phosphorus and potassium in order. A fertilizer mix labeled 10-20-10 is a good choice for petunias.
While fertilizing is one of the most important aspects of plant care, maintaining proper soil pH, appropriate to the types of plants growing in a given flowerbed, is essential. Fertilizer use impacts soil pH. Since certain fertilizers are specific to acidic soils, they are ideal for plants that prefer acidic soil, such as azaleas. Small amounts of acidity-promoting fertilizers are suitable for petunias, which prefer a somewhat acidic soil pH.
Although commercial fertilizers are available, gardeners with environmental concerns prefer organic fertilizers. Many organic fertilizers have the appropriate balance of nutrients for optimal petunias, including many liquid organic products. In addition, a well-developed compost has all the nutrients petunias need; apply top-dressing a few times throughout the growing season with good compost -- instead of feeding with traditional fertilizer -- in areas with rich soil.
Amount and Timing of Feeding
Petunias tend to be "hungry" plants, and should be fed weekly. Timing the feeding correctly is also tied to seasons for most flowering plants. Perennials need to go dormant well before frost to avoid frost damage, and thus gardeners need to stop feeding perennials late in the growing season to allow dormancy to happen. Since petunias are annuals, they will not outlast the first hard frost, and dormancy is thus not an issue. Gardeners can safely go on feeding petunias for high performance up until the first hard frost.