Apply a slow-release, 10-10-10 (10 percent each nitrogen, phosphorus and potassium) analysis or other similar fertilizer to the pansy bed just prior to planting. Use 1 tsp. of fertilizer per each square foot of bed, or use 1 tsp. per each gallon of soil in a planter.
Apply 10-10-10 fertilizer to the bed at the same rate as at planting every four weeks while the pansies are actively growing, according to West Virginia State University Extension. Sprinkle the fertilizer between the plants and work it into the top 3 inches of soil. Do not get fertilizer on the pansy leaves, as it may cause damage.
Fertilize potted pansies beginning four weeks after initial planting. Use a 10-10-10 water soluble fertilizer every two weeks, or as recommended on the fertilizer label. Fertilizer leaches from potted plants more quickly so frequent fertilization is necessary.