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, very productive, and hardy in most areas of Iowa. The four types of raspberries commonly grown in home gardens include black, purple, summer-bearing red, and fall-bearing red. There are also several yellow raspberry varieties (cultivars).
Raspberries adapt 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. Planting in raised beds can improve drainage. When selecting a planting site, choose an area that receives full sun. The planting site should receive at least 6 hours of direct sun each day. 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. If possible, remove all wild brambles near the new raspberry planting to prevent the spread of disease.
Purchase virus-free raspberry plants from a reputable garden center or mail-order company. Plants obtained from an old patch are often diseased. Virus-infested raspberries may appear healthy, but grow and yield poorly. Raspberries may be purchased as dormant, bare-root stock or as tissue cultured plants. Tissue cultured plants are small, actively growing plants that are grown in plant cells or plugs in a greenhouse.
In order to obtain top yields, proper spacing of raspberries is essential. Red and yellow raspberries may be planted 1½ to 3 feet apart within the row. Choose the 1½ -foot spacing for earlier maximum plant density and production. The distance between rows should be 6 to 8 feet. For best results, maintain red and yellow raspberries in 1- to 2-foot-wide hedgerows.
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 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 cellar or garage.
Remove 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. Plant red and yellow raspberries 2 inches deeper while black and purple raspberries should be 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.
Actively growing plants should be planted when the danger of frost is past. Harden actively growing plants outdoors for a few days before planting them in the garden. Initially, place the plants in a shady, protected location. Then gradually expose the plants to longer periods of direct sun. If possible, plant them into the garden on a cloudy day or in the evening. After planting, water each plant thoroughly.
If fertilizer was not incorporated during soil preparation, apply a starter fertilizer solution to each plant. Use a water soluble fertilizer following 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 cultivars for Iowa include 'Boyne,' 'Killarney,' and 'Latham.' 'Autumn Bliss,' 'Caroline,' and 'Heritage,' are excellent fall-bearing red raspberries. 'Anne' and 'Golden Harvest' are two good fall-bearing yellow raspberries. The best purple raspberries are 'Brandywine' and 'Royalty.' Black raspberries are not reliably cold hardy in northern Iowa. Good choices for gardeners in central and southern Iowa are 'Black Hawk,' 'Bristol,' and 'Jewel.'