Sprinkle 1 tsp. of 5-10-10 blend fertilizer, or another balanced blend, over each square foot of the viola bed prior to planting. Work the fertilizer into the top 6 inches of soil.
Fertilize the violas every two months with the 10-10-10 blend throughout their lifespan. Sprinkle the fertilizer 6 inches from the base of the plants, then water the bed thoroughly so the fertilizer soaks down to the root zone.
Use a soluble low-nitrogen fertilizer for potted violas. Apply the fertilizer at the package recommended rate every four weeks throughout the growing season.