Raspberries are a favorite of many home gardeners. The fruit can be eaten fresh or processed into jam, jelly, or juice. Surplus fruit can also be frozen.
Raspberry plants are relatively easy to grow and are hardy in most areas of Iowa. They are also very productive. If given proper care, a 100-foot row of red raspberries can produce 100 to 150 pints of fruit.
Raspberries are adaptable to a wide range of soil types. They grow best in well-drained, fertile soils with a pH of 6.0 to 6.8. Raspberries grow poorly in heavy clay or poorly drained soils. Poor soils can often be improved by incorporating well-rotted barnyard manure or compost. When selecting a planting site, choose an area that receives full sun. Avoid shady areas near large trees and shrubs. Also, avoid areas that are heavily infested with perennial weeds. Perennial weeds such as quackgrass are extremely difficult to control in a raspberry planting. All wild brambles near the raspberry planting should be removed to prevent the spread of diseases to the new planting.
Purchase virus-free raspberry plants from a reliable nursery or garden center. Plants obtained from an old patch are often disease infested. Some virus-infested raspberries may appear healthy, but grow and yield poorly. Raspberry plants may be purchased as dormant, bare root or as actively growing plants. Actively growing plants are small plants that have been grown in cells or plugs in a greenhouse.
In order to obtain top yields, proper spacing of raspberries is essential. Red raspberries may be planted 1 1/2 to 3 feet apart within the row. Plant closer together to fill in the row more quickly for earlier maximum plant density and production. The distance between rows should be 6 to 8 feet. For best results, maintain the red raspberry plantings in a 1- to 2-foot-wide hedgerow.
Black and purple raspberries should be planted 3 feet apart within the row. Rows should be spaced 6 to 8 feet apart. Black and purple raspberries grow in clumps and will remain in their original location.
Early spring (late March and April) is the best time to plant dormant, bare root raspberry plants in Iowa. If the planting of dormant, bare root stock must be delayed after purchase, moisten the packing material around the roots of the raspberry plants and store them in a cool location, such as a cellar or garage. Harden actively growing plants outdoors for a few days before planting them in the garden. Plant them when the danger of frost is past. (The average date of the last killing frost in central Iowa is May 5.)
Remove the dormant, bare root raspberry plants from storage when ready to plant. If the roots of the raspberry plants are dry, soak them in water for several hours before planting. The raspberry plants should be set slightly deeper into the soil than they were in the nursery. Red raspberries are planted 2 inches deeper while black and purple raspberries are set 1 inch deeper than previously grown. Dig a hole slightly larger than the spread of the plant's root system. Position the plant in the center of the hole, spread out its roots, then backfill with soil. Firm the soil around the roots as you backfill. Water each plant thoroughly, then prune back the canes, leaving a maximum of 2 to 3 inches above the soil.
The actively growing raspberry plants should be hardened outdoors for a few days before planting them. Initially, place the plants in a shady, protected site. Then gradually expose the plants to direct sun. Plant them into the garden on a cloudy day or in the evening. Keep the plants moist and protect them against strong winds.
The dormant, bare root and actively growing raspberry plants benefit from the application of a starter fertilizer solution at planting. Use a water soluble fertilizer according to label directions or dissolve 2 or 3 tablespoons of a complete garden fertilizer such as 5-10-5 in one gallon of water and apply 1 to 2 cups to each plant.
Suggested summer-bearing red raspberry varieties for Iowa include Boyne, Liberty, and Latham. Heritage and Red Wing are excellent fallbearing red raspberries. The best purple raspberry varieties are Brandywine and Royalty. Black raspberries are not reliably hardy in northern Iowa. Gardeners in central and southern Iowa should choose from among Black Hawk, Bristol, and Jewel.
This article originally appeared in the March 17, 1993 issue, pp. , 1993 issue, pp. 19-20.