What to Feed Raspberries?

Know Your Soil

• Conduct a soil test in the raspberry patch. Contact your county cooperative extension service for guidelines and costs associated with a soil test. Results from the test reveal what nutrients naturally exist in your garden soil as well as the soil pH. Once you know which minerals are lacking, you can determine which fertilizers are needed for optimal raspberry plant health and maximum fruit production. Loam and clay soils tend to contain more nutrients than sandy soils, which leach more readily after rains and irrigation.

Soil pH

• If the results from the soil test reveal you have overly acidic soil -- a pH below 6.0 -- an application of lime every late winter may benefit the raspberry plants. Lime is particularly good to add to acidic clay to increase the availability of calcium and magnesium to plant roots. The optimal pH range for raspberries is between 6.0 and 6.8. However, these shrubs still produce and perform adequately in soils in the pH range of 5.5 to 7.5. Alkaline soils need to be made more neutral. This is accomplished through acid-forming mulches or fertilizer products to lower the pH.

Fertilizer Types

• Using compost, well-rotted manures and organic mulch in the raspberry patch is beneficial but does not supply ample amounts of nutrients by itself. Typically, raspberries need an application of a synthetic, slow-release fertilizer product twice a year: once in very late winter and again in mid to late spring. Generally, a 10-10-10 fertilizer formula -- often marketed as an "all purpose" fertilizer -- works well. An organic fertilizer product may be used as long as it's a balanced formula, such as 8-8-8 or 12-12-12.

Application Insight

• Apply 10 pounds of granular, slow-release fertilizer to an area of 1,000 square feet in late winter or early spring prior to the appearance of new leaves. If a dense mulch layer exists -- which can slow the decomposition rate and absorb some nutrients -- you may increase the rate to 12.5 pounds per 1,000 square feet. Scatter a second fertilizer application of the same dosage rate in mid to late spring. In the southern United States, mid-April application is timely but apply mid to late May in states nearest the Canadian border. Raspberry plants already have begun developing leaves for about six to eight weeks before this second fertilization is applied.