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| Figure 10. Red raspberry before and after pruning. These canes are planted in a narrow hedge row. |
The basic growth and fruiting habits of blackberries and the three kinds of raspberries are the same. A knowledge of these habits helps in understanding pruning and training principles. Please review the sections in Chapter 1.
The pruning and training of red raspberries differs from that of the other raspberries and blackberries and will be discussed first. Pruning suggestions for summer red raspberries, which have been established for two or more years, follow.
Removing Canes After Fruiting
Because canes die after fruiting, they must be removed. This constitutes a large part of the pruning of raspberries and blackberries. It is preferable to do it in mid-March. Cuts should be made close to the ground. These canes can be cut by mowing, lightly worked into the soil between rows by cultivation, or removed completely and burned.
Thinning Shoots and Canes
From spring to the end of harvest, new shoots and fruiting canes occur together in the row. Competition exists between them for light, water, and nutrients. If competition is severe, new shoot growth is weak, spindly (small diameter), and very susceptible to winter injury. Diseases are favored because of poor air circulation; berry size is poor; and harvesting is difficult. To prevent severe competition, some thinning of both new shoots and fruiting canes is required.
Fruiting canes within the row should be thinned in the early spring when they are dormant. Remove weak canes. Keep large canes that are spaced about four to six inches apart as evenly as possible over the width of the row. Confine row width to 12 to 18 inches (Figure 10). Generally, three to five large-diameter canes per linear foot of row is optimal.
The number of new shoots produced varies with the cultivar and the growing conditions. Certified plants are especially vigorous and produce numerous suckers, particularly the first few years after planting. It may be necessary to mow along the edges of the row during the growing season to reduce the number of suckers. Also, when the old fruiting canes are removed after harvest, some of the weak suckers can be removed by hand. However, the complete thinning job should not be done at this time because this could promote late growth and lead to winter injury.
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| Figure 10. Red raspberry before and after pruning. These canes are planted in a narrow hedge row. |
Heading Back Shoots and Canes
Pinching off the tips (heading back) of young red raspberry shoots in the summer to promote growth of side branches is not recommended. No particular advantages result, and the laterals produced are more subject to winter injury than are unbranched canes.
Heading back of canes (cutting back tops) should be done in the spring (Figure 11). It is preferable to delay this until the extent of winter injury can be determined (after February 15). Ideally, all canes in a row do not require heading back to the same height. Vigorous canes can be left longer than weaker ones. However, in the interests of reducing labor costs, heading back can be done by mechanically mowing at one height. Cane height varies with cultivar and growing conditions. Tall canes (more than five feet) should be cut back to some extent to bring canes down to a convenient height for picking, prevent excessive bending over of canes with the weight of the crop, and increase berry size by reducing the number of berries produced per cane. Head tall vigorous canes four to eight inches above the trellis wire.
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| Figure 11. "Heading back" a red raspberry cane. Do not cut more than the top one fourth or yields will be decreased. |
Because heading back removes part of the potential crop, severe heading back should not be done as the loss of crop will not be offset by increasing berry size. As a guide, a height of 4-1/2 to 5 feet has been satisfactory when irrigation is practiced. A somewhat shorter height may be required when irrigation is not available. When winter injury occurs, all canes need to be cut below the point of winter injury.
With canes shorter than 4-1/2 to 5 feet, heading back is frequently done to remove winter-injured tips or tips severely infected with powdery mildew. Removal of infected tips is an important control measure for powdery mildew. However, when irrigation is available, heading back of short canes to increase berry size does not justify the cost. If irrigation is not available, it is usually sufficient to remove only the weak tip growth as indicated by the close spacing of buds.
Training
Red raspberries are generally grown in "hedgerows" in Ohio. The canes are confined to narrow rows or hedges, and no attempt is made to keep the suckers of one plant separate from those of another. Trellising is generally done in Ohio because vigorous canes interfere with equipment at harvest, particularly in rows that are spaced at less than 12 feet between rows. For trellis options, please see the information on page 39.
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| Figure 12. Permanent trellis posts are spaced about 20 feet apart. Set posts at least 24 inches into the ground. |
Pruning
Red raspberries are the only kind for which fall-fruiting has become economically important. Fall-fruiting red raspberries (Heritage and other cultivars) produce new canes from roots and crown, the same as summer-fruiting kinds, but the upper third to a half of each cane is likely to produce fruit during the first year of growth. Portions of canes that produce fruit in the first year will die after harvest. Portions of the cane that did not produce fruit in the first year will produce fruiting shoots during the next spring, the same as second-year canes of June cultivars.
Dormant season removal of all fruiting canes is done either with a rotary or flail-type mower. The canes can be mowed (one to two inches above the soil) in the spring as soon as weather permits. The canes should be collected and burned to control disease. This converts the so-called "everbearing" or "twice-bearing" kind to a single cropping mode, a fall-crop-only system of management.
Vigorous, early growth of first-year canes is necessary to achieve high fall-fruit-only yields. Such growth results in long canes (4.5 to 5.5 feet) whose tips are laden with fruit.