Raspberry plants are relatively easy to grow. If given proper care, they are also very productive. Important cultural practices include fertilization, watering, and controlling weeds, insects, and diseases.
Established raspberries should be fertilized in the spring before new growth begins. Apply 4 to 5 pounds of 10-10-10 or a similar analysis fertilizer to each 100-foot row. Uniformly broadcast the fertilizer in a 2-foot band. If the raspberries are mulched with sawdust or wood chips, apply a slightly heavier rate (5 to 6 pounds of 10-10-10 per 100-foot row) of fertilizer. Do not fertilize raspberries in late spring or summer. Late spring or summer fertilization encourages succulent, late season growth which is susceptible to winter damage.
Manure may be used as an alternative to commercial fertilizers. Apply 50 to 100 pounds of well-rotted barnyard manure (cow, hog, or horse) to each 100-foot row.
Adequate soil moisture levels are necessary throughout the growing season for good raspberry production. However, the most critical time for moisture is from bloom until harvest. During fruit development, raspberries require 1 to 1 1/2 inches of water (either from rain or irrigation) per week. Insufficient moisture during this time may result in small, seedy berries.
Weed control in raspberries is necessary to reduce competition for water, nutrients, and sunlight. Cultivation and mulches are the most practical control measures for home gardeners. Cultivate the raspberry planting frequently during the spring and summer months. Small weed seedlings are relatively easy to destroy. Large weeds are more difficult . To prevent injury to the roots of the raspberry plants, don't cultivate deeper than 2 to 3 inches.
Mulches help to control weeds and conserve moisture. Possible mulching materials include straw, crushed corncobs, chopped cornstalks, sawdust, wood chips, lawn clippings, and shredded leaves. The depth of mulch needed depends upon the material used. The optimum depth ranges from 3 to 4 inches for fine materials, such as sawdust, to 8 to 10 inches for straw on well-drained soils. Avoid deep mulches on poorly drained soils to discourage root diseases. (When mulching red raspberries, apply the full depth between the rows. Within the rows, apply only enough mulch to control the weeds so new canes can emerge in the spring.) Since mulches gradually decompose, apply additional material each year.
Insect and Disease Control
Good cultural practices should help prevent many insect and disease problems. For example, pruning and removal of the old fruiting canes immediately after the summer harvest removes potential disease inoculum. Also, maintaining red raspberries in a 1- to 2-foot-wide hedgerow helps insure good air circulation and penetration of sunlight. Narrow hedgerows dry quickly after a rain, discouraging disease development. Apply pesticides when insects and diseases start to cause significant damage. Pest control recommendations can be found in Pm-175, The Home Fruit Spray Schedule.
This article originally appeared in the May 21, 1999 issue, p. 64.