Raspberries: Raspberries may be grown successfully at an elevation as high as 7,000 feet. They do best in full sun on non-alkaline “fertile” loam soil. However, they may be grown in partial shade or under other environmental constraints. Natural protection against strong winter winds are provided by some valleys, but in other areas it is necessary to provide artificial protection during winter months (see topic on “Winter Protection”).
Site Selection: A high sloping site will reduce cold injury by allowing the cold air to drain into low areas. However, do not plant raspberries on the crest of a hill due to the drying effect of wind. Winter-kill is often caused by wind desiccation instead of low temperature. Raspberries grow well on a wide range of soil types. The character of the subsoil is more important than the type of surface soil. The subsoil should be deep and well drained. The root system will be restricted if the subsoil is underlaid by a shallow hardpan or a high water table. Plants with restricted root systems may be damaged during drought periods because raspberries need an abundant supply of moisture at all times. Raspberry roots and crowns are also extremely sensitive to excessive moisture in poorly drained soils. Flooding for 24 hours or longer may kill the roots by suffocation. Young plants may appear to grow well the first season on poorly drained soils but injury symptoms will occur during the following seasons. Well drained loamy soils are usually most productive. The lighter textured sandy soils are easiest to cultivate but must be frequently watered and fertilized. Select a site at least 300 feet from other bramble crops to minimize transfer of virus diseases. Additionally, eliminate any wild bramble plants found within several hundred feet of the planting. Tomatoes, potatoes, eggplants, peppers, and brambles are all susceptible to many common diseases. Do not plant raspberries after these crops. If possible, set raspberries on sites that were planted to cultivated crops the previous year. When sod fields are used turn under the sod the season before planting.
Preparing the Ground: Unfortunately, raspberries are poor competitors. After choosing the best soil and site be sure to destroy all perennial weeds. Weeds may be destroyed with cultivation, herbicides, and/or landscape fabric mulch. Before working small areas, cover the ground with a black plastic mulch and place soil, rocks or other weighty objects on the edges to hold it in place. A good time to lay the landscape fabric is in the fall or early spring (March). Leave it there for six to eight weeks to help control weeds before working the soil.
Planting: Obtain plants from a reputable nurseryman, or a patch that is free of virus disease. Keep the plants cool and moist until they are planted. They may be stored for several days in cold storeage at 35 degrees F. Plant raspberries as soon as the ground can be worked early in the spring. It is better to delay planting than attempt to work wet soil. Space hills approximately two feet apart, or if in partial shade, about three and one-half feet apart. Place plants in holes five to six inches deep and fill holes with soil and press firmly. Keep the soil moist. Generally, two complete growing seasons are required before the plants grow large enough to produce an appreciable amount of fruit.
Pruning: Red raspberries need to be pruned annually. Two main reasons for pruning are to remove dead canes and to thin out the clumps. New canes grow annually and produce fruit the following year, then die. Dead canes should be cut at ground level and removed. A healthy stand of raspberries will produce numerous new canes annually. They may become so dense that some canes are weak and produce little or no fruit. It is better to remove the weaker ones and leave six to ten large canes per hill. This should be done in July or August when the new crop of canes are young and tender. Other pruning may be necessary to remove suckers which come up out and away from the hill or row. Generally, cultivation and mowing will keep suckers under control. If a natural planting is desired suckers, or side shoots, may be allowed to spread freely as in the wild. Do not mow, cut, cultivate or control the suckers if room is available for this type of planting. Dead tips of raspberry plants may be removed in the spring or early summer.
Support of Canes: Unless the raspberries are the trailing varieties, the plants will stand erect. They will often bend over if they are grown in shaded or windy areas. Partial support is often necessary to keep plants upright. A tight wire, rope, nylon cord or any strong material on each side of the row will give good support. In some cases it may be necessary to provide support between the hills. Tie a short piece of cord or wire across the row with both ends connected to two long strands for support.
Fertilizer: Raspberries use large amounts of nitrogen, phosphorous and potash. They use lower amounts of calcium and sulfur and even lesser amounts of trace or minor elements such as iron, zinc, magnesium, boron, manganese and copper. It is wise to have your soil tested and to mix up a complete and well balanced fertilizer. A general application of fertilizer containing equal amounts of the three primary foods of nitrogen, phosphorus and potassium is recommended when a soil test is not available. A mix containing approximately 20 percent of each primary element is usually available at commercial outlets. Weigh out about one pound for every 35 feet of linear row and spread it in a strip extending two feet past the row and two feet on each side. For a 35-foot row of plants this is an area 39′ x 4′ or 156 square feet. Weigh out only about two-thirds of a pound for the 35-foot row if the fertilizer analysis is higher. Conversely, weigh out about one and one-fourth pounds for a 35-foot row if the nitrogen content is low. Many fertilizer mixes contain enough sulfur with the three primary plant foods to satisfy plant needs. Most soils in Montana contain adequate calcium. Additionally, many fertilizer mixes contain adequate calcium.
Irrigation: Raspberries use more soil moisture than most fruit plants. Irrigated plants are more vigorous and yield fruit over a longer season than do unirrigated plants. Begin irrigating raspberries at the same time other garden crops are normally irrigated. Most cultivars require about one inch of water per week during the growing season. Extreme warm and windy conditions make greater amounts of water necessary. Light sandy soils need more frequent irrigation than heavier clay soils. The fruiting period is a critical irrigation time. Apply 1 to 1 1/2 inches of water once a week if drought occurs during fruiting. Do not over water in late summer or fall. Excessive water application during this time may delay maturity of cane wood and result in a freezing injury that will become evident the next spring.
Winter Protection: There are several ways in which raspberries become damaged or killed during winter months. They are:
Winter Drought – This drying process during subzero weather is common in Montana. Water the plants in late fall before the ground freezes (usually October or November) to reduce or avoid this damage. Provide protection against wind whenever possible.
Break of Dormancy – Whenever the temperature of the atmosphere reaches 41 degrees F (5 degrees C) for three or four days raspberries break dormancy and become active. When a winter warm spell is followed by a sudden hard freeze it kills the active tissue. The top portion of the canes break dormancy first. This is why many canes with dead tops are evident in the spring. To avoid this, wrap the canes with burlap or similar material to reduce the intensity of winter sun and wind. When possible, build a temporary fence to cast shade on the plants. Additionally, cover the ground around the plant with straw or other insulating material to reduce the intensity of the freezing period. Mulching reduces root injury which results in less root rot. Do not leave the mulch, shade or wrapping on too late in the spring. Usually these materials should be removed around the first of April or sooner in the lower elevations of the state to avoid injury.
Raspberry Rust – This fungus disease is easily detected. The undersurface of the leaves will be covered with a bright orange-colored mass of spores. The disease will stunt and weaken plants. Upon first appearance of this rust, dig the plant out and burn it. Spray the remaining plants with a fungicide such as daconil or captan or dust them with sulfur or any other reommened fungicide on the market. Do not eat fruit containing any of the fungicide. Read and follow the directions and precautions on the container label carefully.
Anthracnose – The symptoms of this fungus disease are circular, reddish-brown, sunken spots up to 1/4 inch across on young shoots. A slot-hole effect on the leaf develops late in the season. Individual droplets (seeds) or larger areas on fruit may remain reddish and hard as the fruit matures. The fruit may be deformed. It is very important to have clean plants to control this disease. Remove and burn infected plants immediately and spray the remaining plants with a fungicide as for raspberry rust.
Spur Blight – This fungus disease usually occurs on shady sites and in patches where canes are very dense or numerous. It seldom exists on sunny locations where canes receive adequate sunlight. Symptoms include brown or chocolate colored spots on canes at the base of the leaf petioles. Leaves usually drop off. The brown circular spot formed at the leaf scar continues to enlarge until most of the cane turns brown. It is essential to have raspberries in a sunny location and keep canes thinned out to control this disease. Spraying the plants with Bordeaux 4-4-50 or Daconil will reduce the spread of this disease, but the thinning of the canes and admission of sunlight is the first control measure. Burn diseased canes.
Rhizoctonia – This is a fungus disease which injures roots. Normal raspberry roots, when washed appear white or nearly so. Brown roots may be indicative of the disease. The outer portion or epidermis is dead if the roots appear brown. Rhizoctonia may be the casual organism causing this damage. It is very difficult to control. Because it tends to invade frost-injured roots it may be reduced by controlling the extent of winter freezing. This is done by applying a mulch over the crowns and soil surface within two feet of the plants.
Mosaic – The symptoms of this virus disease are large greenish blisters surrounded by yellowish tissue on the leaves. Leaves are smaller than normal and crinkly. These symptoms are obscured by hot weather. The best control is to use disease-free plants. Remove and burn diseased canes. Control leaf-feeding aphids because they may spread the disease.
Probably 75 % of the raspberries in the United States are the red type. Red raspberries are more hardy than black or purple raspberries. There are only a few protected areas in Montana where black and purple raspberries do well.
Red Raspberries: Boyne is a mid-season berry that was developed in northern Minnesota. It is extra hardy and bears large fruit. It is a top commercial variety in some northern states. Fruit are borne on dwarf canes that are easy to pick. Boyne is an excellent plant maker and may bear a week or ten days before Latham. Berries are succulent with large dark red fruit. Heavy cropper.
Latham is one of the most popular and dependable mid-season raspberries. The canes are very vigorous, productive and cold-hardy. The large red berries darken as they mature. Latham is a late-season variety with a fairly long harvest season. Ripens mid to late season. Berries are extra large and are good quality for fresh use and/or freezing.
Nordic produces excellent crop of firm red berries in mid summer. It is a deep red, juicy fruit that is good fresh, frozen or for jam. It is similar to Boyne except for its much superior disease resistance, especially to anthracnose. The fruit is slightly smaller but the yeild and fruit quality is comparable.
Red Wing is a fall bearing raspberry that has firm medium size red fruit. Responds well to complete spring cane removal which shifts production entirely to fall harvest. It will reach fall harvest 2-3 weeks earlier than Heritage. The quality and size is similar to Heritage and aphids are minimal.
Red Ever-bearing Raspberries
Amity is a medium growing spreading, deciduous broadleaf perennial. With a height 3-6′ and spread of 3-6′. It likes sun and is hardy to about -30 degrees F. The white flowers that bloom in summer produce a very firm, medium to large ever-bearing, red berry. It is considered nearly thornless. It has some mildew and other disease and large raspberry aphid resistance. Production is somewhat higher and begins maturing up to a week earlier than Heritage.
Heritage is an excellent fall-bearing red raspberry. It is very vigorous and suckers prolifically. Canes usually do not require support. The fall-crop berries are medium-sized and very firm unless produced under rainy conditions.
Fall Gold is a medium growing, spreading deciduous, broadleaf perennial with a height of 3-6′ and a spread of 3-6′. It likes sun, and is hardy to about -20 degrees F. The white flowers produce golden yellow, sweet and juicy raspberries in summer. These are extra large, conical berries and are born in large clusters. They are hardy, ever-bearing and very productive, an excellent all purpose raspberry.