Fertilize raspberry plants in early spring before new growth appears, using 2 to 3 lbs. of 10-10-10 fertilizer for every 100 feet of plants. Spread the fertilizer along the row and work it into the soil with a garden tiller or a hoe, and take care not to disturb any roots.
Repeat in May or June before raspberries bloom or set fruit, following the same application rate and procedure.
Test the soil every three years to determine the nutritional needs and pH of the soil. Contact your local cooperative extension service for a soil test kit. The office provides soil testing for a minimal fee. The results outline the condition of your soil, available nutrients and the pH level of your soil. Follow instructions for amending the soil, applying lime or other amendments with the first application of fertilizer.