Extension Horticultural Specialist
Department of Horticultural Science
North Carolina Cooperative Extension Service
North Carolina State University
In the case of specialty or non-traditional small fruit crops in the Southeast, red raspberries seem to get the most interest and coverage by newspapers and popular press. In North Carolina, red raspberries developed in northern United States and southern Canada have difficulty in our hot, humid summer climate of the piedmont and coastal plain. And, in the foothills and mountains of western North Carolina, the raspberry 'floricanes' are especially prone to winter freeze injury as temperatures in these areas may fluctuate in January and February by as much as 40-50 F in a given 24 hr period. Dormanred and Southland are red raspberries with southern adaptation and both show promise in the coastal plain, sandhills and lower piedmont regions of North Carolina where "northern" raspberries do not survive. In the upper piedmont and mountains, Heritage, the "everbearing" variety, is a possibility for the home garden, but it is too disease susceptible for commercial recommendation. Red raspberries have erect canes with the exception of the variety Dormanred that is trailing.
Black raspberries or "blackcaps" may tolerate somewhat higher summer temperatures and be adapted to a wider area in North Carolina than red raspberries, but they are quite susceptible to several serious disease problems including anthracnose, crown gall, orange rust, and virus diseases. Black raspberries have arched canes.
Purple raspberries are hybrids of red raspberries and blackcaps. They have the same growth characteristics as blackcaps. They are presently grown in western North Carolina, though the area they are adapted to is about the same as the blackcaps.
Some raspberries have yellow fruit. Yellow raspberries are variations of red raspberries, and except for fruit color, have all the characteristics of red raspberries. They are grown chiefly by homeowners in northern states.
Besides taking care to select only raspberry varieties which have been successful in your area, be sure to buy plants from a reputable nursery. Tissue cultured plants are preferred because they are certified virus free and should be free of Verticillium wilt and crown gall. Dormant canes are not recommended because experience has shown that they are often disease infected. Be cautious about accepting plants from a neighbor's garden. All raspberries are self-fertile and may be planted alone. Plants of red and black raspberries should be separated by 700 ft.
Table 1. Raspberries Suggested for Trial in North Carolina Variety Area Season Plant Fruit Red Raspberry Southland Mtns. June & Erect, 2 crops Light red, U. Pied. mid-Aug. annually. good quality. Dormanred All June Trailing habit Glossy red, large, vigorous fair quality. Heritage Mtns. June-Aug. Erect, ever- Deep red, U. Pied. bearer good quality. Black raspberry Allen Mtns. June Erect, earlier Large, firm than Bristol. berries. Bristol Mtns. June Erect, susc. to Large, good anthracnose. quality. Cumberland Mtns. June Erect, ripens Large, exc. with Bristol. quality. Purple raspberry Royalty Mtns. June-July Erect, v. Cone-shape U. Pied. vigorous fruit,sweeter than Brandeywine.
The canes of raspberries are biennial -- they grow for one year and then produce flowers and fruits during the early summer of the second year. The second year canes die shortly after harvest, and should be pruned out as soon as harvest is over.
All raspberries produce new canes, called primocanes, to replace those that die. Red raspberries produce primocanes from crownbuds and from buds along roots (root suckers). The root suckers come up at random and result in a thick bramble patch if not controlled. Black and purple raspberries produce primocanes only from crown buds on the original plant and so remain where you first plant them.
Most raspberries produce fruit on second year canes (floricanes) primarily in June and early July, depending on variety and location. Some red raspberries are everbearing, such as Heritage and Southland. These varieties produce fruit on the primocane tips in late summer of the first year. The second year they produce berries on lower portions of floricane that had not fruited the previous season. It is recommended that Southland red raspberry be allowed to bear its two crops annually; however, with Heritage red raspberry it is better to eliminate the June crop completely in order to maximize the late summer primocane crop.
Heritage may be annually pruned by simply mowing or cutting off all canes at or slightly below the soil surface late each fall. The following spring, new shoots (primocanes) will begin to grow. These canes will produce fruit on the tops in late summer through early fall.
Raspberries grow best on deep, sandy-loam soils well supplied with organic matter. They may be grown in any good garden soil provided it is well drained to a depth 3 ft and has high moisture holding capacity. Although the pH of the soil is not that critical, a range of 5.8 to 6.5 is considered optimum. Select a site where tomatoes, potatoes or eggplants have not been grown. Also, a planting should not follow directly after a sod but rather the planting should follow a cultivated or cover crop. If the soil lacks organic matter work 1 inch or more of organic residues such as lawn clippings, rotten leaves, or well rotted manure into the top 4 to 6 inches of soil. Before planting mix about 3 pounds of 10-10-10 or equivalent fertilizer per 100 square feet of soil.
Order tissue cultured plants so that they arrive close to the last spring frost date in your area. Dormant cane plants are usually obtained and planted in the spring about 4 weeks before the average date of the last frost. Work the soil as for garden vegetables, particularly where the plants are to be set. If plants arrive before soil preparation or when the soil is too wet for planting, store the plants--if well wrapped--in a cool place. If unpacked, heel dormant cane plants into the ground in a shallow trench in a cool shady area so roots do not dry out.
Red raspberries are planted 3 ft apart in the row with 8-10 ft between rows. Black raspberries are set 2-1/2 ft apart with 8-10 ft between rows being adequate to prevent spread of fungus diseases which tend to be prevalent with the plantings in closer rows.
Set tissue culture plant "plugs" in the ground to a depth of about 3 inches; dormant cane plants are set 5 to 6 inches deep, or at least 1 inch deeper than the plants were grown in the nursery row. The removal of the dormant cane plant "handles" to the ground level on black and purple raspberries will aid in control of anthracnose. A trellis to hold canes upright is strongly recommended in the home garden for red raspberries. Stretch heavy gauge, rust-proof wire between the posts at 5 ft, two wires at 2-1/2 ft and 5 ft are not necessary for the trailing red raspberry Dormanred. A crossbar trellising is recommended for most other upright red raspberries. If you string two wires at the same height, place them 4 ft above the ground level. Place the canes between the wires to eliminate tying. If you use a single wire, or one wire above the other, tie the canes loosely to the wires after pruning. The black raspberries need not be tied to trellis support or stakes; they are topped several times in summer at approximately 30 inches to keep them from growing too tall.
If the everbearer Heritage red raspberry is to be grown for one crop in late summer, you can also construct a temporary trellis to provide raspberry canes some support for the crop. A simple method is to set stakes in the row at 15 to 20 ft intervals. Tie binder twine to the end stake and then fasten to each stake down the row. Repeat on the opposite side of the row. If canes are very heavy, tie the two lines of twine together at intervals.
Most red raspberry varieties can be grown in hedgerows. The canes are confined to narrow rows or hedges that are maintained about 15 inches in width. During the growing season, it is desirable to allow root suckers to develop in a row 12-15 in. wide, but it is important to pull out suckers growing up outside the row.
Do not pinch or cut off tips of new shoots in summer or fall. Summer tipping encourages growth of side branches which are not desirable on red raspberry plants.
Cane height varies with variety and growing conditions. Floricanes usually need to be cut back to some extent before bearing. Do this in the late winter. Heading back to 5 ft makes a good height for picking and helps keep canes from bending over under the weight of the crop.
Fruiting canes and new shoots occur together in the row from spring to the end of harvest. They compete for light, water, and nutrients. Usually, more canes and shoots occur than are wanted. They must be thinned or the new shoots will be weak, berry size will be poor, harvest will be difficult, and diseases will be more serious.
Thin fruiting canes in late winter or early spring before they start to grow. Remove all weak canes and thin the strong canes so they are 4-6 inches apart over the width of the row; narrow rows if necessary to 15-18 inches wide.
Remove fruiting canes at the end of harvest. Do it soon after harvest, mainly to help control diseases. Make cuts close to the ground, also thin new shoots at this time, leaving 3 or 4 of the sturdiest canes per foot of row. If you use a single wire or one wire above the other type trellis, or stakes, tie the canes loosely to the support structure after summer pruning.
Dormanred red raspberry with trailing canes are somewhat more difficult to manage than erect types. The trailing primocanes should be tied to a stake or trellis after the second year canes have produced their crop, so the soil can be cultivated or mulched.
These plants do not need trellises or support if they are pruned as outlined here.
Summer tipping -- Cut off the tips of new shoots in the early summer. This tipping is done when individual canes reach a height of 30 inches. All shoots do not reach the right height for tipping at the same time. Toward the end of the first season, the canes send out laterals. The next season small branches grow from buds on laterals. Fruit is borne on these small branches.
Dormant Pruning -- The laterals (side branches) which result from summer tipping may be as long as 3 feet or more. If all were left, berries would be small and of poor quality. Cut the laterals back so that two buds per lateral are left on thin diameter canes, up to six buds per lateral on stout canes.
Thinning Canes -- In late winter remove canes that are under 1/2 inch diameter. Healthy plants should have from 2 to 5 canes that are over 1/2 inch, but if all canes are smaller than this, cut out all but the largest ones.
Removal of Canes After Fruiting -- After fruiting, canes die. They should be cut out as out-lined for red raspberries.
Blossom Removal -- After planting, remove blossoms which appear the first summer on Heritage and Southland red raspberries. This helps plants become well established.
Weed Control, Cultivation and Mulching -- Keep plants in rows free of weeds by hand weeding, hoeing and cultivation or with a mulch. Raspberries may be grown under clean cultivation, sod or permanent mulch. The author prefers the mulch. The average homeowner has many organic residues around the home such as lawn clippings, leaves, or shredded vegetation. A raspberry planting is an ideal place to use these materials.
If you grow raspberries under clean cultivation, the area between rows is cultivated to a depth of 1 to 2 inches at intervals of 2 weeks from early spring to end of harvest. This controls weeds and red raspberry suckers in the row. If you use sod culture, mow the area between one row like a lawn throughout the summer to control growth of weeds, grasses and suckers. Where a permanent mulch is used, mow at timely intervals to control raspberry suckers between the rows.
Highest yields will likely be obtained with permanent mulch. Clean cultivation is next highest yield, and sod usually results in the lowest yield, but is easy to maintain for a homeowner.
In colder regions of the state it is quite likely that the canes and buds of Dormanred will be winter injured if left up in the air in an exposed condition. In late fall untie canes from the trellis wires or stakes and lay them on the ground before the ground freezes to protect them from winter injury. Covering the canes with mulch should not be necessary.
Plants need about 1 inch of water a week from bloom time to end of harvest. Plants should also be watered during prolonged dry periods after harvest as well. When watering, add enough water to wet the soil to a depth of 6 to 8 inches.
Many insects and diseases damage rasp-berries. You can avoid many pest problems by:
Contact your Cooperative Extension Agent for current recommended spray programs or refer to your North Carolina Agricultural Chemicals Manual.
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.