AMES, Iowa – Raspberries are popular with many home gardeners. They’re easy to grow, and perform well in much of Iowa. However, gardeners can run into issues with heat, weeds and pruning that curtail yields.
ISU Extension and Outreach horticulturists can help answer your questions about how to best handle raspberry plantings.
Should I water my raspberries during dry weather?
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 1½ inches of water (either from rain or irrigation) per week. Insufficient moisture during this time may result in small, seedy berries. During dry weather, thoroughly water raspberry plants once a week.
Soak the soil to a depth of 10 to 12 inches. If possible, avoid wetting foliage and fruit to reduce the risk of disease problems. Soaker hoses and drip irrigation systems are excellent ways to water raspberries. If overhead watering is unavoidable, water raspberries early in the morning. Morning applications reduce the amount of water lost due to evaporation and allow the plant foliage to dry quickly.
How do I control weeds in my raspberries?
Cultivation, hand pulling and mulches are the most practical weed control measures for home gardeners. Cultivate the raspberry planting frequently during the spring and summer months. Small weed seedlings are easily destroyed. Large weeds are more difficult to control. To prevent injury to the roots of the raspberry plants, do not cultivate deeper than two to three inches.
Possible mulching materials include straw, chopped cornstalks, sawdust, wood chips, dry grass clippings and shredded leaves. The depth of mulch needed depends on the material used. On well-drained soils, the optimum depth ranges from three to four inches for fine materials, such as sawdust, to eight to 10 inches for straw. Avoid deep mulches in poorly drained areas to discourage root diseases. Since organic mulches gradually decompose, apply additional material each year to maintain the desired depth.
Is it necessary to prune raspberries in summer?
Pruning raspberries in summer helps control diseases. It also helps maximize next year’s crop.
After the last summer harvest, promptly remove the old fruiting canes of red, purple, and black raspberries at the soil surface. To help reduce disease problems, the pruned material should be removed from the garden and destroyed.
Pinch out or cut off the shoot tips of black and purple raspberries when the new growth reaches a height of 36 to 48 inches. Remove the top three to four inches of the shoots. Removal of the shoot tips encourages lateral shoot development and increases the fruiting surface area, resulting in higher yields.
Since the new shoots will reach the specified height at different times, go over the planting approximately once each week between late May and late July. Discontinue shoot tip removal at the end of July. Canes that develop after July are small, weak, and unproductive. These small, weak canes can be pruned out the following spring.