In favorite fruit polls, fresh raspberries top the list for desirability. In addition to simply tasting scrumptious, they are high in fiber and vitamin C. Brightly colored fruits like strawberries and raspberries are high in a natural substance called ellagic acid, a compound which may help lower risk for cancer. In growing raspberries for making preserves, the toughest chore is to make sure they are not immediately eaten! Consumed fresh, they can be used on cereal, over ice cream, in pies, in tarts and in fruit smoothies. The remaining fruits make outstanding jams which can be enjoyed mostly through the winter months, teasing taste buds for another fresh crop of fruit in the upcoming growing season.
Raspberries need about the same physical conditions as strawberries: well-drained soil, full sunlight, free airflow and soil rich in organic matter. To be productive, raspberries need to have their fertility level maintained, as nutrient-starved plants are poor producers. Consequently, about five to eight pounds of a 10-10-10 fertilizer per 1,000 square feet need to be worked into the soil prior to planting of the brambles. At the onset of new growth, scatter about 1/4 cup of the same material in a circle 10-12 inches from each plant. Fertilizer applications should continue each year the crop is being managed: fertilize in April/May as new growth is just beginning, and again after harvest. With the right cultivar selection and proper care, the home gardener can expect up to 1,500 pounds from a half-acre of plants, or about two quarts per plant.
Good management efforts will keep the raspberries productive for five to eight years before viruses take the plants out completely, or reduce production to a level that isn’t worth picking. Productivity can be maintained by continually replacing those plants that show a decline or viral symptoms, and replacing them with new offshoots from plants displaying vigorous growth and ample fruit production. Plants grown mostly on a north-facing slope will stay dormant longer in the spring and spread their bearing period out a little longer than those grown mostly on a south-facing slope. They also will be less subject to late spring frosts due to better cold air drainage.
While this is true for the red and purple summer-bearing raspberries, fall-bearing cultivars are better planted on a south-facing slope to allow for faster maturation and greater assurance of having a harvest. Refer to Table 2 for cultivar selections.
Table 2. Raspberry cultivars hardy for cold climates (Zone 3).
Summer Bearing |
Boyne |
Killarney |
Latham |
Madawaska* |
Newburgh* |
Fall Bearing |
Fall Red |
Heritage |
Nordic* |
Reveille* |
|
* Trial in ND only; tested in WI and MN |
Raspberries grow and produce fruit in a rather unique manner. They are actually biennially growing canes on perennial root systems. This means that the first year, the canes (called primocanes) do not produce fruit, but form flower buds along the canes and their branches. The following season, these canes (called floricanes) produce flowers — and fruit — and then die.
Being shallow-rooted plants (70 percent of the root system is in the upper 10 inches of soil), raspberries would typically need supplemental irrigation to be consistently productive in most areas of the Upper Midwest. It is an extra expense, but well worth it for the extra quality and quantity that is evident in the developing fruit.
Inquiries often come in about raspberry canes producing fruit in August or September from the same plants that produced fruits in early July. While they might be the same plants, they are not the same canes; the fall fruit production is actually coming from primocanes that would normally bear the following season. What happens is that the primocanes grow and produce a certain number of nodes. The growing tip then changes from a vegetative state to a reproductive one. Will those same canes produce the next season? Yes, just not from the same area on the cane. The fruit borne on the upper cane will be small; the fruit borne the following season in the mid-section of the cane will be much bigger and sweeter.