In most areas of the country, pansies are treated as an annual flower. In other regions, they can last for a long time, and are treated as a perennial. In either case, your pansies will do better if you fertilize them properly. Fertilize these flowers when you first plant them and then either monthly or bi-monthly thereafter, depending on whether you use a granular or liquid fertilizer.
Use an all purpose fertilizer for flowers. West Virginia University Extension Service recommends using a balanced fertilizer, such as 10-10-10.
Sprinkle the fertilizer around the plants, at a rate of 1 tsp. per square foot of flower bed, as suggested by West Virginia University Extension Service. If plants are potted in containers, use less than this—about half a tsp. per 10-inch container. Apply this to the soil only; avoid getting any on the plants or you risk burning them.
Water the soil gently with a garden hose or your watering can. Re-apply fertilizer once a month.
Mix liquid fertilizer with water in your watering can. Follow the directions on the bottle as dilution requirements will vary, and how much solution you need to make up depends on the size of your flower bed (or how many containers you have).
Stir the mixture with a spoon to ensure it is mixed well.
Apply the liquid fertilizing solution on the area around your pansies. Try to avoid dripping or splashing fertilizer on the plant itself.
Re-apply the liquid as indicated by the label. This may be as soon as two weeks. Liquid fertilizer usually must be applied more often than granular fertilizers.