Of the hundreds of varieties of petunias, many have the same or similar care requirements. Petunias are well-suited for the home garden because of their ease of care, variety, color and fragrance. These annual flowers can be easily grown in containers or planted directly into a sunny spot in the garden.
Fertilizers for petunias contain nitrogen, which promotes leafy growth and provides the leaves with green coloring. Nitrogen deficiency may cause yellowing and growth failure. Fertilizers also contain phosphorus, which strengthens the petunia's stems and causes the roots to grow strong and hardy. Phosphorus deficiency may result in lower quality plants. Another main component in petunia fertilizer is potassium. Potassium aids in winter hardiness and disease resistance. Lack of adequate potassium may increase disease susceptibility.
Feed petunias a well-balanced fertilizer with equal amounts of nitrogen, phosphorus and potassium. A 10-10-10 mixture works well.
Use a solid fertilizer with a time-release formula in the beginning, later switching to a liquid fertilizer as petunias grow. Make the change in mid-summer, or in approximately the middle of the growing season.
Mix perfectly balanced time-release fertilizer in with the soil prior to planting petunias. Use approximately 2 lbs. of fertilizer for every 100 square feet of soil. Once you have begun using liquid fertilizer on petunias, continue using it once every three weeks during the growing season. Petunias that grow by spreading will require more frequent feeding.
For fertilizer instructions specific to your soil type, visit your local county extension office with a soil sample or purchase a soil test kit at a garden center or hardware store.
Do not over-fertilize your petunias as this may cause yellowing, poor growth, disease susceptibility and loss of foliage.