Apply about two ounces of a 5-10-5 fertilizer around each plant. Starting the second season and annually thereafter, fertilize raspberries in early spring before growth begins. Apply a balanced fertilizer, such as a 10-10-10, at a rate of 15 to 20 pounds of fertilizer per 1,000 square feet of planting. If using the hill system, apply about one-half cup per plant. Don't fertilize raspberries in late summer or early fall as it may force new growth that does not harden off properly for winter.